The concept of the Vertebrate Pest Conference originated in early 1960 from discussions among representatives of the University of California; the California Dept. of Fish & Game; the California Dept. of Agriculture; the California Dept. of Public Health; and the Branch of Predator and Rodent Control, Bureau of Sport Fisheries and Wildlife, U.S. Fish & Wildlife Service. The original participants recognized that few published documents on vertebrate pest control were available, as such information was typically contained within in-house reports of the various agencies that were largely unavailable and unable to be cited. Dr. Walter E. "Howdy" Howard of UC realized that having a conference would permit a Proceedings to be published, in which this information could be made widely available.
To plan such a conference, the organizing group, chaired by Dr. Howard, became the Vertebrate Pest Control Technical Committee, which arranged and hosted the first "Vertebrate Pest Control Conference" held in Sacramento on February 6 & 7, 1962. The planning committee formally became an incorporated non-profit entity in 1975, and the Vertebrate Pest Conference is now held in late winter or early spring every two years. It is the most widely-recognized conference of its kind worldwide.
Detailed histories of the development of this Conference are found in these publications:
Volume 28, 2018
The history of discoveries in rodenticide development and control technology as well as current and future-focused research are explored. Traps and older poisons such as red squill, arsenic, and cyanide have been used for hundreds if not thousands of years. Between 1940 and 1980 there was a period of innovation with the discovery of new molecules, including acute toxins and slower acting anticoagulants. The period 1980 to 2018 has been a time for improved utilization of individual tools and research to retain registrations, develop new toxins and delivery systems, and explore non-lethal control options. However, despite these advances, decades old broad-spectrum toxins and traplines are still the mainstay of pest control. Technological leaps are needed to achieve much more precise, affordable, and socially acceptable pest control. The period 2018 to 2050 should be a time for accelerated innovation. There are exciting opportunities for transformational change based on the integration of existing and new tools, such as advances in automated species recognition systems, new self-resetting traps, and species-specific toxin-delivery systems. Over-reliance on 'silver bullet' technologies for small mammal pest control is the wrong approach to biodiversity conservation. This has been demonstrated through two decades of challenging research on viral vectored immunocontraception, and would apply if all pest control research focused on a single toxin, one new engineering-based technology, or on gene editing, which has potential, but will not be a panacea for all mammal pests. Balance is important, with research supporting the skill of pest control practitioners and supporting emerging technologies, as well as novel biocontrol or genetic research. There has been no focused research aimed at integrating a broad suite of new tools, and incorporating disruptive technologies from completely different fields. We believe that science and technology have now advanced such that automated, online, and real-time systems for monitoring and managing pests are achievable in the next decade.
The goal to make New Zealand ‘Predator Free,’ articulated as the eradication of rats, stoats, and possums by 2050, was announced as a New Zealand government initiative in 2016 and became a founding initiative for the International Union for Conservation of Nature (IUCN) Honolulu Challenge on Invasive Species. A new government owned company, Predator Free 2050 Limited (PF2050 Limited), was formed to coordinate partnership approaches to large landscape projects and breakthrough science. Consultation of both the general public and conservation stakeholders in New Zealand has given strong confidence of majority support for the Predator Free 2050 initiative, and both its target species focus (rats, stoats, and possums) and goal (landscape-scale eradication for the outcome of native biodiversity protection and restoration). A logical and robust process of research strategy development to help realise the Predator Free goals has been ongoing since 2012, when seven priority strategy and research areas were identified at a ‘Pest Summit’ workshop of researchers and stakeholders convened by the New Zealand Department of Conservation. The workshop also highlighted that past improvements in the ability to manage small mammalian pests have been driven by multiple complementary and often synergistic strands of research. The critical learning from such back-casting is that if the Predator Free 2050 goals are to be achieved, a similarly diverse research portfolio is essential moving forwards to drive the paradigm shift from current mainland predator suppression approaches to mainland predator eradication. This learning was implemented in construction first of a research project on small mammal management in the New Zealand’s Biological Heritage National Science Challenge, and, more recently, of PF2050 Limited’s research strategy. With the remit of focusing research efforts to achieve a breakthrough science solution capable of eradicating at least one small mammal predator by 2025, the strategy has four programmes (‘Environment and Society,’ ‘Best Use of Existing Approaches,’ ‘Exploring New Approaches,’ and ‘Computer Modelling’) designed to complement existing efforts to give the whole portfolio of relevant research the best chance of achieving the 2025 goal.
Harnessing Population Genetics for Pest Management: Theory and Application for Urban Rats (Abstract)
Effective management of rodent pests requires an ecological understanding of how they move through their environment, and how those movements influence the invasion, persistence, or reinvasion of problematic colonies. Traditional methodologies used to describe rodent movement patterns, such as mark-recapture, are hindered by their time-consuming nature and limited geographic scope. As such, our understanding of how rodents interact with urban environments remains limited. Population genetic principles and tools have the capacity to greatly increase our understanding of rodent population dynamics, ecological relationships, and movements across space but this field is often unapproachable to non-scientist pest management professionals. In this paper we aim to promote collaborative and integrative rodent pest management by introducing relevant population genetic principles, providing examples of their applications in studies of urban brown rats, and proposing future initiatives that link scientific, private, and government entities. Using a densely-sampled brown rat population in the city of Vancouver, BC we show how genetic relationships among individual brown rats can be leveraged to understand the geographic distribution of genetic clusters (i.e., colonies), natural barriers to migration, and the spatial scale of dispersal. We describe how these results can be exploited by PMPs to directly inform the creation of management units and decrease the likelihood of rapid post-treatment reinvasion. Further, we discuss the difficulties inherent in population genetic studies and the potential for high-quality model sites to develop generalizable strategies. Overall, we hope to expand the toolbox of pest management professionals, foster collaboration, and move towards more informed and sustainable management strategies.
Olfactory lures are important pest control tools, being widely used to attract animals to detection devices, traps, and poisons. For small mammals, like commensal rodents, almost all lures are foods. For invertebrates, however, semiochemical lures predominate and have done so for decades. Semiochemical lures overcome the inherent limitations of food-based lures, such as their perishability and inconsistent odour properties, and poor performance when foods are abundant. They can also provide benefits like low cost, ease of handling, and in-field longevity. Semiochemical lures for rodents would be a major advance, like that achieved for invertebrate monitoring and control, but their discovery has been constrained by the complexity of the challenge. Our research group is the first to achieve animal response-guided semiochemical lure discovery. We statistically integrated rapid field-based bioassays with scent chemical profiling and partial least squares regression to identify and test a suite of new single- and multi-compound rat lures. Field trials identified a tetrad and dyad mixture as the best performing lures, with an attraction rate of 0.61 and 0.60, respectively, compared to an attraction rate of 0.55 for the peanut butter standard. In total, 17 compound-based lures performed statistically as well as the peanut butter standard. We are currently working with an industry partner to encapsulate the lures as consumable, cost-effective pest-control products. Semiochemical lures will be particularly useful for multi-kill traps, toxic bait delivery devices, and remote monitoring devices that could operate for long periods without intervention. These devices offer substantial control program cost reductions but require long-life lures to realise their full potential.
Urban Field Efficacy of a New Cholecalciferol-based Soft Bait on Commensal Rats in New Orleans, Louisiana, USA
Selontra® Rodent Bait (BASF, Ludwigshafen, Germany) is a cholecalciferol-based soft bait that exhibits high palatability both in the lab and field. Because of the attributes and mode of action of cholecalciferol, isolated field populations of rodents can often be controlled by Selontra within one week after initial bait exposure. Baiting trials were established at five sites in the city of New Orleans, Louisiana to investigate the field efficacy of Selontra against roof rats (three sites) and Norway rats (two sites). Comparison of pre- and post-baiting census data indicates an average control rate of 97.7% for roof rats and 88.5% for Norway rats.
Your Children Mite Not be Safe at School: An Outbreak of Biting Rat Mites at a Southern California Elementary School Campus
During May, 2017, the Orange County Mosquito and Vector Control District (OCMVCD) received anonymous calls from distressed school staff and parents of children attending an elementary school (Villa Park Elementary School, VPES) in Orange County, California, about an outbreak of pruritic dermatitis that was believed to be caused by biting arthropods. The incident received intense media coverage and led to a partial closure of the campus. With no identified culprit, OCMVCD interviewed VPES staff and surveyed the school property for vertebrate pests and their ectoparasites to determine the source of the outbreak. After thorough inspections of the exterior and interior of classrooms and a carefully-placed, glue-board trap survey, OCMVCD detected signs of significant roof rat activity (feces, rub marks, and harborage sites) throughout the campus and the presence of rat mites inside multiple classrooms. OCMVCD worked with other governmental agencies (Orange County Health Care’s Environmental Health, California Department of Pesticide Regulation’s School Integrated Pest Management Program, local city officials) and the VPES administration to educate parents about the vertebrate pests on the school grounds and the complexities of controlling the rat mite infestation during the school year. OCMVCD also identified deficiencies in the school’s pest control program and developed an integrated vector management plan to address the immediate and long-term health threats to prevent rodent and rat mite outbreaks in the future. This report details the investigation and methodology used to locate and eradicate the vertebrate and ectoparasite threats on the VPES campus and the challenges encountered during the process.
Rodenticides are an essential tool in the integrated pest management (IPM) of infestations of commensal rodents. With the introduction of Assembly Bill 2422 California Natural Predator Protection Act, the State of California is potentially facing a future with serious restrictions on the use of anticoagulant rodenticides to manage commensal rodents in urban areas. Assembly Bill 2422 has been proposed to protect predators from rodenticide poisoning and seeks to significantly restrict the application of first and second generation anticoagulant rodenticides for use in many urban and no-urban areas of California. Exclusion and cultural practices, such as landscape management and sanitation, are important and successful tools for managing rodent populations. However, quick and efficient control of commensal rodent infestations often necessitates the use of rodenticides. While rodenticide is an important tool, exposure of wildlife to anticoagulant rodenticides has been evident for many years in the state of California. When rodents are consumed by predators, second generation anticoagulant rodenticides can be detected as residues in the livers of predators. Many species of animals are documented as having succumbed to rodenticide toxicosis, however the effects of chronic, sub-lethal exposure to predators are not well understood. This paper will discuss the current and proposed changes to rodenticide legislation in California, impacts of the legislation on communities across California, and gaps in research preventing the adoption of evidence-based best management strategies for rodent control. In order to improve the success of commensal rodent control programs in California, effective strategies for rodent management must be developed.
Norbormide is a rat specific toxicant. It causes vasoconstriction of small arteries and vasodilation of large arteries in rats, which results in a rapid fall in blood pressure and death from heart failure. It is an extraordinary compound in that it is only toxic to rats. The lack of toxicity of this compound to birds and other mammals is unique. It was originally researched in the 1960s and initially marketed in the USA. Problems with taste aversion slowed its continued use and sales it and was largely forgotten when anticoagulant rodenticides became more effective and popular. Following the emergence of anticoagulant resistance in some populations of rodents, residues of the second-generation anticoagulants in wildlife and concerns regarding humaneness, interest in non-anticoagulants, such as norbormide, has revived. Research has been conducted to help identify and understand a formulation of norbormide which is palatable, effective, and fast acting in rats. Further research is underway to determine methods for large scale synthesis of an improved form of norbormide. Field trials are planned in 2018/19. The ability to target rats with no risk to non-target species presents considerable advantages in many settings and warrants further investment and completion of the current scale-up phase of research and development.
Effectiveness of Snap-trapping, Goodnature A24 Automated Traps, and Hand-broadcast of Diphacinone Anticoagulant Baits to Suppress Invasive Rats (Rattus spp.) and Mice (Mus musculus) in Hawaiian Forest
Invasive rodents (rats and mice) commonly occur on islands and often damage natural resources largely by predation of native species. Suppressing invasive rodent populations and their damages is therefore a common practice in many parts of the Hawaiian Islands, and land managers such as the Army Natural Resources Program on Oahu often control rodent populations by using large-scale rat snap-trapping and Goodnature A24 automated rat traps (henceforth A24s). While rat traps can be effective at suppressing rat populations, mouse populations are not generally suppressed and may expand greatly. In an effort to reduce rodent populations to levels below that accomplished with rat traps alone at a 5-ha mesic forest on Oahu (Ohikilolo), we assessed the effectiveness of a one-time (two application) hand-broadcast of anticoagulant (Diphacinone-50) bait pellets applied at 13.8 kg/ha per application while A24s and rat snap-traps were active. We monitored rat and mouse activity during trapping and before, during, and after the bait applications using tracking tunnels, which are baited ink cards placed in tunnels so that foot prints of animal visitors can be identified. We found that rat trapping alone was effective at reducing rat populations but not the mouse population, and that the one-time hand-broadcast of diphacinone bait reduced both rat and mouse activity to 0% tracking for about 1 month. However, rat and mouse populations rebounded 2 months later to 15% rat tracking and 41% mouse tracking, which were roughly pre-treatment levels. Rat suppression using A24s at Ohikilolo appeared much more effective year-round than at a nearby 26 ha site (Kahanahaiki), though mouse suppression was poor at Ohikilolo relative to Kahanahaiki. The hand-broadcast of diphacinone bait at both Ohikilolo and Kahanahaiki was effective but short-lived, so repeated baiting during the seasonal peaks in rodent abundance and increasing the size of the buffer area would more likely protect target natural resources from rats and mice.
The County Service Area (CSA) 1984-1 for Vector Control was established in June 1984 to serve the public’s needs for providing a comprehensive vector control program throughout Alameda County. In 1987, the City of Oakland recognized that it had a severe rat problem emanating from the sanitary sewers, and in an effort to control them the voters approved a supplemental assessment. For thirty years the CSA has implemented an urban rodent surveillance program focusing on monitoring and controlling commensal rats (Norway and roof rats) and mice in residential, commercial, and business properties. In 2017, the CSA received 2,917 Requests for Service from the public about domestic rodents (2,282 re: rats and 635 re: mice), representing 38.9% of overall service requests. Those 2,917 rodent service requests had staff biologists performing 16,722 field services operations related to rodents. The field service operations included performing smoke and dye tests of sewer lines for breaks; field and residential surveys for rodent activity; recommendations and follow-up evaluations of rodent control measures; and assistance with enforcement actions. In 2017, a total of 8,150 sewer inspections and 1,531 applications of Contrac rodenticide bait were made in the City of Oakland. The CSA is now looking at incorporating rodenticide resistance testing, GIS data analysis, pulse-baiting strategies, and disease surveillance as part of an Integrated Pest Management program as improvements in 2018.
Alameda County Vector Control Services District (ACVCSD) receives ‘requests for service’ (RFS) relating to a variety of potential vectors of disease; one of the major program groups is rodents, which include house mice, deer mice, Norway rats, roof rats, wood rats, tree and ground squirrels, and meadow voles. This is an overview of the events of 2016, and some data from 2017, which began with much-needed rain and Alameda County bloomed. Along with an increase in biomass came an overabundance of rodents. The much-needed rainfall has historical correlation to meadow vole RFS and led to new records of meadow vole requests for services, and then to an unprecedented influx of house mice from open fields into neighborhoods. Our 2009 record-high 31 meadow vole requests for service was dwarfed by our 46 requests for service in 2016, which is almost a 50% increase over the 2009 high and over 4 times higher than the 10-year average of 9 RFS (some years had no meadow vole RFS). Additionally, in 2016 we received an astounding 637 house mouse RFS, an increase of over 73% of any of the previous 10 years which averaged 312 per year; the next-highest house mouse year generated 367 RFS. What seems to have accelerated the skyrocketing house mouse calls for service was one severely-affected Livermore neighborhood’s use of a neighborhood-networking website, which a neighborhood activist used to spur the residents to contact us for intervention. Our first indications of unusual problems for residents living in Livermore, and to a lesser extent in Fremont, followed three days of heavy rainstorms in mid-October produced nearly 10 inches of rainfall in some parts of the Bay Area, which exceeding the average monthly rainfall. We subsequently we received 257 rodent-related service requests.
Cattle grazing lands in the mountainous western United States are rugged, complex, and extensive. Terrain, vegetation, and other landscape features vary greatly across space. Risk of wolf-cattle encounters and potential for depredation loss certainly differ spatially as consequence of this variability. Yet, our understanding of this spatial risk is quite poor and this knowledge gap severely hampers our abilities to manage wolf-livestock interactions and mitigate conflicts. During 2009-2011, a research study was conducted at four study areas (USFS cattle grazing allotments) in western Idaho to evaluate and predict risk of wolf-cattle encounters. Each year, a random sample of 10 lactating beef cows from each study area was instrumented with GPS collars that logged positions at 5-minute intervals throughout the summer grazing season. Cattle resource selection was modeled using these GPS data and negative-binomial regression. An existing model was used to classify habitats within the study areas in terms of probability of use by wolves as rendezvous sites. Efficacy of this model was confirmed using scat, telemetry, and rendezvous site data. Spatial overlaps in the predicted selectivity of wolves and cattle were assessed and study area landscapes were then classified into five encounter-risk classes (very low to very high). Concurrent wolf and cattle GPS tracking data were used to document wolf-cattle encounters and thus evaluate the accuracy of this classification. About 94% of observed wolf-cattle encounters occurred within either the high or highest encounter-risk classes. Areas classified to the highest risk class were located on smooth, relatively flat slopes in concave terrain (e.g., stream terrace meadows) but not all were associated with surface water. Having this predictive understanding of where wolf-cattle encounters are most likely to occur will allow livestock producers and wildlife managers to more effectively apply resources, husbandry practices, and mitigation techniques to reduce conflict.
After centuries of persecution, European wolf populations are recovering across many areas due to favorable legislation and the rise of the “rewilding” movement over the past few decades. The central mechanism triggering the rewilding of Europe was the European Union Habitat Directive, approved in May of 1992. The directive classifies the wolf as a strictly protected species and all EU-countries have implemented the directive in their legislation. Since the 1990’s, the number of wolves in Europe has steadily increased and the total number of wolves, excluding Russia, Belarus and Ukraine, exceeds 12,000 wolves. At the same time conflicts between farmers, wolf protectors and authorities are becoming more frequent. Wolves living in Central Europe, Finland and Scandinavia must cope with the fact that there are human settlements throughout their habitat. This results in a strong habituation to humans and a growing number of attacks against cattle and sheep under the cover of darkness as well during dawn, dusk, and night. The appearance of wolves in settled areas in broad daylight seems to be more and more the rule rather than the exception. While authorities explain this as being a part of the wolf's normal behavior, human tolerance in areas where wolves return is rapidly lowering. Wolves’ depredation on livestock, and especially a behavior called surplus killing, has resulted in several clashes between farmers and authorities in France and Italy. Surplus killing is a behavior exhibited by wolves in which they kill more prey than they are able to consume and then abandon the remainder. Incidents from Southern Europe show that a single wolf pack may kill hundreds of sheep in one single attack. In this paper I will review the implications of human-wolf coexistence in settled areas in different parts of Europe. I will highlight a number of problems experienced as well as solutions and their outcome.
Direct and Indirect Impacts to Ranchers from Wolves and Other Predators: Building a Baseline in California
While the direct economic impacts of gray wolves and other predators on rangeland livestock production are relatively easy to measure, indirect impacts (e.g., reduced livestock productivity and increased expense) may be more economically significant. We initiated a long-term (10 year), longitudinal survey of rangeland cattle, sheep and goat producers in northern California to quantify the direct and indirect impacts from gray wolves, which are increasing in numbers in the state, and other large carnivores on rangeland livestock production. During winter/spring 2017, we hosted seven producer-researcher workshops across northern California, featuring livestock-predator conflict experts. At these workshops, we collected the first round of survey data from 90 livestock operations. Our initial survey results document the adoption rates, efficacy and cost of a variety of commonly used livestock protection tools on rangeland livestock operations at a variety of scales.
As wolves recolonize across their former range in western North America, encounters between livestock and wolves are expected to increase in frequency. Understanding the physiological state of the prey, as a response to stress imposed by the presence of a predator (trait-mediated effects), will help with predicting the total effect of predators on their prey beyond direct consumption (density-mediated effects). Fecal glucocorticoid (GCM) is widely used to measure stress response, but provides inconclusive results, particularly when applied to a finer spatio-temporal variation in predation risk (i.e., wolf-livestock encounters). Since the impact of external stressors (i.e., wolf encounters) on the body influences ultimately the physical and metabolic state of the animal, we purpose to investigate: 1) if the fecal metabolome extracted from cattle fecal samples reflects changes in the GCM levels, and 2) if the cattle metabolome can better predict stress response than GCM post-wolf encounter. We first performed a controlled stress experiment on five captive cows in a pasture. We also conducted a field study in Washington where we fit GPS collars equipped with proximity sensors on two wolves in two separate packs, and on 40 range cows in four different livestock herds. When a wolf and a cow equipped with proximity sensors are within 128 meters from one another, the GPS collars send a real-time message that allows us to assess the physiological state of the prey at a finer spatial-temporal scale. In both studies, we collected fecal samples from GPS radio-collared cattle and compared their metabolome to GCM levels. Our results clearly show that the metabolomic analysis of the cattle gut microbiome can better predict acute stress response than the GCM, in both the controlled and free-ranging environment.
Ranch management has become more complex since wolves were reintroduced into Idaho and Wyoming in 1996. In wolf areas, livestock have experienced increased death loss and greater stress. Increased livestock aggressiveness has been observed, especially toward working dogs, making handling livestock more difficult. Additionally ranchers have reported a loss of body condition, lower conception rates, increased time and expense for management. Our study was designed to investigate the effect of wolf presence on cattle behavior, landscape use patterns, and resource selection by comparing high wolf density areas against low wolf density areas. This study also generated baseline information on cattle spatial behavior before wolves were on the landscape. A Before-After/Control-Impact Paired (BACIP) experimental design was used. Control study areas in Idaho (3) have high wolf presence while Impact study areas in Oregon (3) started with no wolf presence, and are shifting to elevated wolf presence. Paired Idaho and Oregon areas have similar topography, vegetation composition, wild ungulate prey bases, and livestock management. Cows are tracked at 5-minute intervals using GPS collars (10 per area) throughout the grazing season. Wolf presence is monitored by GPS, trail cameras, and scat surveys. Ten GPS-collared cattle in an Idaho study area encountered a GPS-collared wolf 783 times at less than 500 meters during 137 days in the 2009 grazing season. At 100 meters there were 53 encounters; 52 at night. Tests of naïve and experienced cattle exposed to a simulated wolf encounter found increased excitability and fear-related physiological stress responses in cows previously exposed to wolves. This was shown through increased cortisol levels, body temperature, and temperament scores. Cattle presence near occupied houses doesn’t offer protection from wolves. Data shows wolves within 500m of occupied houses 588 times during 198 days of tracking. Many confirmed depredations on this site were also close to houses.
The wild pig is well known for its generalist diet, a contributing factor to its successful invasion around the globe. We used DNA metabarcoding analyses of scat to examine wild pig diet on a cow-calf operation in south-central Florida. This 4,249-ha ranch is comprised of improved pastures and semi-native pastures that contain a mosaic of vegetation types. Both pasture types contain numerous wetlands and ditches as well as oak-palm woodlands. Fecal sampling was conducted along transects from March 2016 to February 2017. The study site was divided into five sampling areas to ensure dispersed sampling across the ranch. At least five freshly deposited scats were collected every two months from each sampling area and frozen. Regions of multiple genes that targeted either animal or plant DNA (CO1, trnL, and 12S rRNA marker genes) were selected for high throughput sequencing. Sequences were identified using the GenBank reference database. Two hundred nineteen fecal samples were collected and 196 were analyzed. Consensus lineages were retained if they could be confidently identified to family and were likely intentionally consumed by a pig. Between the three marker genes, 66 plant, 68 animal, and 12 fungal families were identified. Plant species dominated the diet with oak, torpedograss, joyweed, Bahiagrass, dayflower, and other grasses occurring in over half the samples analyzed. Animals were present across a wide taxonomic breadth, but encountered less frequently than plants with the exception of an exotic earthworm. Cattle, house mouse, cotton mouse, raccoon, mole cricket, Virginia opossum, and six species of fly were recorded from over 10% of fecal samples. This represents the first study to employ DNA metabarcoding to examine the dietary composition of this invasive vertebrate across an entire year.
Biomarkers have been used to quantify consumption of toxicants and other pharmaceutical baits by free ranging wildlife populations. Previous research has tested the efficacy and persistence of Rhodamine B (RB) as a biomarker in invasive wild pigs. However, little information is available about effects of RB on palatability of baits meant for invasive wild pigs, and studies have shown that the addition of RB to otherwise palatable baits reduces consumption by some species. HOGGONE® has been identified as an effective sodium nitrite-based oral toxicant for invasive wild pigs in trials conducted in captive pen trials. We simultaneously conducted five separate 2-choice tests to examine potential differences in consumption between HOGGONE® placebo paste (standard placebo) and HOGGONE® placebo paste containing 0.5% RB (RB placebo) in five groups of three invasive wild pigs. Each group was simultaneously presented with equal amounts of standard placebo and RB placebo paste for one night and monitored with remote cameras. Remaining bait was weighed and subtracted from the initial weight of both feed types to calculate consumption. There were no differences in the total amount of bait consumed or the time spent feeding between the two bait types across all five groups. Results of this study suggest that the addition of RB does not negatively impact consumption of HOGGONE® placebo paste by groups of invasive wild pigs. Thus, we provide more evidence that RB will be a useful tool for research on wild pigs, such as estimating proportions of free-ranging populations consuming baits that contain toxins or pharmaceuticals.
The distribution of feral hogs throughout North American has increased dramatically since their introduction. The use of toxicants has proven to be a n effective tool in controlling feral hog numbers in several countries. Using data from 13 GPS hogs, we compared movements and space use of control and treated hogs between pre-baiting and baiting phases of 3 feral hog toxicant field tests. Generalized linear mixed models were used to explain prospective changes in movements. In addition, we evaluated the distance of toxicant-killed feral hog carcasses from bait stations, roads, and cultivated crop plots. The mean distances traveled by treatment hogs between the pre-baiting and baiting periods was reduced by 43.9%, 32.1%, and 48.8% for daily, diurnal, and nocturnal periods, respectively. Daily and nocturnal movements exhibited a significant decrease between pre-baiting and baiting phases by feral hogs as a result of bait consumption. Mean space use size between the pre-baiting and baiting periods for treatment hogs was reduced by 37.5% and 30.0% for 95% MCP and 50% MCP, respectively but was not a result of bait consumption. Toxicant-killed feral hog carcass distance from bait stations, cultivated crops, and roads averaged (± SE) 919.4 ± 68.1 m, 908.9 ± 72.1 m, and 120.7 ± 34.9 m, respectively. These carcasses were never recovered from crop plots or near roads and were typically found in natural land cover types. The toxicant warfarin reduced movements of feral hogs, which in turn can reduce their damage to crop and reduce the spread of disease.
The feral hog is an invasive species that inflicts billions of dollars in agricultural damage every year in the U.S. Hog-specific baits have shown promise in reducing feral hog abundance but require species-specific feeders to exclude domestic animals and non-target wildlife. Four feeder types were tested during 2016 and 2017 field studies, including commercial feeders, prototype feeders, and a new species-specific feral hog feeder. Commercial feeders with 2.3 kg, 4.5 kg, and 6.8 kg weighted doors were used in 2016 and raccoons were observed on camera opening doors 10 times out of 164 camera observed visitations (6.1%). No other non-target species were observed entering the feeders. The following year, new feeders with 7.7 kg double-sided guillotine doors were used in a field study and no raccoons opened doors during 153 camera-observed visitations. Out of over 1,600 non-target camera images recorded, only one mouse was observed inside the feeders. Results of this study suggest the new hog feeder may provide reduced-risk to non-target species and a promising tool for controlling hog populations.
Invasive wild pigs (Sus scrofa) are a widely distributed and destructive invasive species throughout parts of North America, Australia, South America, Africa, and many island nations (Barrios-Garcia and Ballari 2012). The invasion of wild pigs is associated with extensive agricultural, ecological, and control costs (Hone 1995, Pimentel et al. 2000, Pimentel 2007). Wild pigs are expanding in distribution and population density throughout the United States and Australia (Bevins et al. 2014, Lewis et al. 2017, Snow et al. 2017b). These increases are attributed to intentional and accidental introductions by humans (Spencer and Hampton 2005, Barrios-Garcia and Ballari 2012), high reproductive potential (Mayer and Brisbin 2009), lack of predators (Bevins et al. 2014), human alterations to the landscape that improve suitability for wild pigs, and the adaptability of wild pigs to occupy a variety of landscapes and opportunistically feed on many food items (Seward et al. 2004). An international effort to develop an acute and humane toxic bait for invasive wild pigs is underway to assist in curtailing their expansion (Snow et al. 2017a). We evaluated the ability to expose a population of wild pigs to a simulated toxic bait (i.e., placebo bait containing a biomarker, rhodamine B, in lieu of the toxic ingredient) to gain insight on potential population reduction. We used 28 GPS collars and sampled 428 wild pigs to examine their vibrissae for evidence of consuming the bait. Overall, we found that (74.1%) of wild pigs tested were positive for RB from consuming the RB bait. These wild pigs were sampled from an average distance of 0.61 km (SE = 0.04) from the nearest bait sites. We estimated that 91% of wild pigs within 0.75 km of bait sites (total area = 16.8 km2) consumed the simulated toxic bait, exposing them to possible lethal effects. Bait sites spaced 0.75-1.5 km apart achieved optimal delivery of the bait, but wild pigs ranging ≥3 km away were susceptible. Use of wild pig-specific bait stations resulted in no non-target species directly accessing the bait. Most of the collared wild pigs visited >1 bait sites during the final night with biomarker deployment, leading to two relevant conclusions. First, the 18-day baiting strategy for locating, and accustoming wild pigs to the placebo bait and bait stations, was adequate for overcoming neophobic tendencies of wild pigs. Secondly, the spacing of the bait stations (i.e., 1 bait site per 0.75 km2) was adequate for exposing all wild pigs in between bait sites to the bait, and may have been expanded to expose more wild pigs. This study demonstrated the potential for exposing a large proportion of wild pigs to a toxic bait. Bait sites should be spaced 0.75-1.5 km apart, and closer will provide better efficacy. Approximately 18 days of coordinated pre-baiting should be sufficient for accustoming wild pigs to using the wild pig-specific bait stations and readily consuming a novel bait. Toxic baits may be an effective tool for reducing wild pigs especially if used as part of an integrated pest management strategy. Investigation of risks associated with a field-deployment of the toxic bait is needed.
Wild pigs in North America carry multiple pathogens capable of causing diseases in wildlife, people, and domestic animals. Wild pigs are the reservoir host of pseudorabies virus (PrV) which is a fatal infection in wild carnivores. We previously conducted surveillance for PrV in wild pigs from Kern County, California where the distribution of wild pigs overlaps with native mountain lion. We found that 100% of wild pigs were exposed to PrV, and 6% were shedding the virus. Black bears and pumas have been observed preying on wild pigs in the region suggesting that they are vulnerable to exposure to PrV from pigs. We conducted retrospective, post-mortem surveillance for PrV on 16 pumas from five counties in south central California. None of the pumas tested positive for PrV. In Florida, PrV is attributed to one-third of the deaths in Florida panthers. Wild pigs are a large portion of the diet of panthers in Florida, but studies in California suggest pigs may not be utilized as frequently. This difference in diet could account for the lack of evidence that PrV causes measurable mortality in California pumas. Nonetheless, in management areas with carnivores, wild pig management should be carefully considered.
In 1978, Point Reyes National Seashore (PRNS) reintroduced Tule elk, which is the only National Park unit where Tule elk can be found. The State of California provided the initial elk Tomales Point in PRNS. State wildlife biologists were members of the team that managed the re-introduction and subsequent monitoring. Tomales Point is a fenced area; however, one goal of the 1998 Tule Elk Management Plan was to establish a free-ranging Tule elk herd to the seashore. That plan stated the forage is unaffected by the number of elk occupying the range and elk do not have a strictly negative effect on vegetation. However, in 1999, PRNS moved a free-range herd of 28 elk from Tomales Point to the wilderness area near Limantour Beach. Within weeks, a few elk unexpectedly migrated to ranches in the designated pastoral zone. Currently, Drakes Beach (D Ranch) herd includes approximately 150 Tule elk. Designated pastoral zone, where livestock and dairy producer operations may be permitted, are charged an annual lease based on the lands’ carrying capacity. In 2004, beef and dairy producers began to express concerns about the impacts elk were having on forage, organic certifications, and overall economic viability. In 2014, PRNS initiated the Ranch Comprehensive Management Plan to assess growing concerns of beef and dairy producers related to the free-ranging elk impacts to the pastoral zone. PRNS staff have not implemented any of their 1998 control methods, and are currently only hazing elk away from permitted operations. The efficacy of hazing elk away from the pastoral zone is in question; and PRNS has stated an inability to do more control due to recent litigation. Efforts should focus on non-lethal effective elk management options, such as contraception, which abide by current litigation constraints while mitigating producer burden and concern. The objective of this paper is to develop a case for potential multi-species management (i.e., elk plus cattle) at PRNS while protecting its historical, biodiversity, and economic value.
Interpreting Feral Goat (Capra hircus) Movement to Guide Management in a Mesic Watershed on Oʻahu, Hawaiʻi
Endemic Hawaiian ecosystems evolved without ungulate herbivores. Feral goats, a common nonnative ungulate on Pacific Islands, browse and trample vegetation which can denude watersheds and expose them to soil erosion. Since 1993, the Hawaiʻi Division of Forestry and Wildlife has actively suppressed feral goat populations to protect critical watersheds in a 1600-ha management area on Mount Kaʻala in the leeward Waiʻanae mountain range of Oʻahu. Despite these ongoing efforts, total eradication has not been achieved to date. This study examined the movement patterns of one male and one female feral goat in this management area over one year in 2015-16 with GPS collars. The primary objective was to determine if feral goat movements are related to seasonality, moon phase and precipitation to inform future management efforts. The male goat exhibited a large range, extending out 2.5 km from its starting point and over an 800m elevation range within the year, traveling to lower elevations during the summer months. The female goat, in turn, had a much smaller range and stayed relatively close to its initial starting point. The male goat exhibited greater movement at night than during the day, and this was particularly evident during full moon phases; animals also exhibited aversion to movement during precipitation events. Hot spot analyses showed that the female was largely confined to one location throughout the course of the study, while the male moved to multiple locations but displayed a strong affinity to the eastern portion of the management area in the Fall season. These initial findings help build knowledge on local patterns of feral goat movement within this managed area that can be used for control efforts. GPS collars provided useful high-resolution data to support further adoption of this technology to better inform management decisions. Future management strategies should incorporate longer-term movement data sets from multiple individuals to better understand habituation (e.g., return to favored locations), patterns of sexual segregation and rutting. This would allow a more demographic approach for maintaining populations below levels that are considered detrimental to this critical habitat.
Cost-Benefit Analysis of Mountain Lion Management for the Recovery of Endangered Sierra Nevada Bighorn Sheep
We evaluated the consequences of different predator management strategies and the subsequent effects on time and cost to recovery for federally endangered Sierra Nevada bighorn sheep. Based on data collected during 1995-2009, we used stage based demographic modeling to estimate vital rates in three isolated herds, accounting for sampling error and variance. Using those vital rates we predicted the time and associated cost for the population to meet delisting goals. We found recovery time increased from 17.3 to 28.6 years using a density independent model and from 25.9 to 38.6 years using a density dependent model for different mountain lion management strategies. Commensurate cost increases of over 10 million dollars (unadjusted cost) result in either case. Our study suggests that appropriate levels of predator management will result in shorter recovery times and reduced cost of recovery through ensuring the availability of translocation stock. To be most effective, mountain lion management strategies should be population-specific because of underlying differences in predation rates for different herds.
A Proposed Analysis of Deer Use of Jumpout Ramps and Wildlife Use of Culverts along a Highway with Wildlife Exclusion Fencing
Highways can fragment habitat and be a significant mortality source for mammals. Wildlife exclusion fencing has been shown to reduce wildlife-vehicle collisions, but can also prevent animals from escaping the highway corridor if they enter at access roads or at fence ends. Earthen escape ramps, or “jumpouts,” have been proposed as a possible solution but remain relatively untested. From 2012-2014, we used wildlife cameras to continuously document wildlife use of four jumpout ramps constructed as part of a 2.5-mile wildlife exclusion fence project along Highway 101 near San Luis Obispo, California. Mule deer occasionally used the jumpouts, but quantifying the rate of utilization was confounded by repeated visits by the same individuals. Male and female deer appeared to have different responses to the jumpouts, which warrants deeper investigation using additional data collected from further monitoring through mid-2017. The longer dataset will also better document how individual deer learn to use the jumpouts. Fenced highways can also reduce connectivity unless there is sufficient use of crossing structures. We documented mountain lion, bobcat, black bear, and mule deer used culverts and underpasses in and adjacent to the wildlife fence zone from 2012-2014. Mule deer used the large underpasses almost exclusively, and rarely if ever used culverts. Bear used a wider variety of structures, and bobcats were detected at almost every site and at a higher rate than the other taxa. Mountain lion detections were quite rare, likely due to lower population density in the study area. We propose a deeper multivariate analysis of the factors influencing these species’ use of culverts including culvert dimensionality, nearby habitat, and proximity to cover, based on an expanded dataset of up to five years of continual monitoring at certain sites. The goal of these analyses is to provide information that will help reduce wildlife-vehicle collisions while facilitating regional wildlife connectivity.
The U.S. Federal Aviation Administration's (FAA) National Wildlife Strike Database (NWSD) documents reports of civil aircraft collisions with wildlife in USA. The NWSD has been managed by the Wildlife Services Program of the U.S. Department of Agriculture through an interagency agreement since its inception. Although the NWSD includes about 170,000 reports of civil aircraft collisions with wildlife (97% birds) from 1990-2015 (14,000 in 2015), the overriding focus has been the quality control of data entered for over 90 variables ranging from species and numbers of wildlife struck, location and time of day, phase and height of flight, aircraft type, components struck and damaged, effect of strike on flight, and associated costs. This attention to detail allows the NWSD to be used in multiple ways to document the nature of the problem temporally and spatially for individual airports and nationwide. The NWSD is used by individual airports and FAA Airport Certification Inspectors to help objectively evaluate and improve Wildlife Hazard Management Plans by examining adverse-effect strike rates (number/100,000 aircraft movements) and the species causing those damaging strikes. The NWSD provides supportive evidence and guidance to state and federal agencies for issuing permits for wetland mitigation and removal of wildlife at airports. Nationally, the NWSD provides a science-based foundation for FAA regulations and Advisory Circulars related to wildlife management at airports and airworthiness standards for engines and aircraft components. In addition, the NWSD provides unique opportunities for basic research on topics such as bird migration (height and location of strikes) and bird behavior in relation to aircraft lighting. For example, recent research has shown that birds are more likely to strike the left side of aircraft where red navigation lights are located. The NWSD is a living document, continuously refined with new and revised strike events to enable improvements to aviation safety in an environmentally responsible, science-based manner.
To Live and Fly in LA: Using Bird Strike and Management Program Information to Improve Safety at Airports in the Los Angeles Basin (Abstract)
Wildlife-aircraft collisions (wildlife strikes) pose a serious safety risk to aircraft. Wildlife strikes can be evaluated at different levels, include efforts to examine these problems at the national, regional, or state level, or for an individual airport. Similarly, wildlife strikes involving individual wildlife species or guilds can be examined at varying scales. Although wildlife strike analyses at the national, regional, or species/guild level are valuable, airport-specific analyses are essential for the effective implementation and evaluation of integrated wildlife damage management programs as these actions are conducted at the airport level. The species that present hazards to safe aircraft operations varies among airports, even when considering airports that are very close to each other (spatially). We developed a strategic planning framework to increase the efficacy and appropriateness of wildlife hazard mitigation programs, using the three Los Angeles World Airports as examples. This framework is intended to be simple, adaptable, and useful to airport wildlife biologists and their co-operators (i.e., airport manager and operations personnel). First, we reviewed the airport-specific wildlife strike information to determine if trends or patterns exist. Second, we categorized the wildlife species (primarily birds) based on their direct mitigation potential, feeding behaviours, seasonality, and migration patterns. Lastly, we reviewed the graphs of direct mitigation actions that were conducted each year. Using each individual airport’s wildlife strike data, direct mitigation effort information, and the life history/ecological characteristics of individual wildlife species, we devised a matrix of four categories (i.e., I to IV) to simply the evaluations, thus allowing us to group wildlife species or guilds according to their behavioural patterns and direct mitigation potential. Species included in Category I are those species that are invasive, are resident (i.e., non-migratory), and have a moderate to high direct mitigation potential. Category II includes species that typically have a semi-resident or migratory life history and have moderate direct mitigation potential. Species that are migratory and are winter residents at the airports but have a low to moderate direct mitigation potential were included in Category III. Category IV species are typically summer residents at the airports or migratory oceanic waterbirds with minimal to low direct mitigation potential. For each wildlife species of interest, we graphed the number of reported wildlife strikes (for non-damaging, minor damage reported, and substantial damage reported) for each year using information extracted from the Federal Aviation Administration’s National Wildlife Strike Database. Risk values (i.e., low/medium/high) were assigned to each individual wildlife species of interest based on the frequency of damaging strikes that occurred at each airport. We graphed the available direct mitigation data involving each wildlife species of interest at each airport. Direct mitigation actions included lethal removal of problematic individuals, live-trapping and translocation of problematic individuals, and non-lethal hazing. Once each wildlife species or guild of interest was subjectively classified into one of the four categories, strategic planning efforts can be conducted to evaluate and modify an airport’s wildlife damage management plan and activities. Recommendations regarding the potentially most effective direct and indirect mitigation recommendations can then be made for each category based on the findings related to the wildlife strike information and direct mitigation activities previously conducted at the airport.Our efforts resulted in a simple, adaptable, and useful strategic planning framework to conduct airport-specific planning and evaluations of wildlife damage mitigation actions. However, because our approach is flexible, there is great potential for modification and improvement (depending on the wants and needs of a specific airport program). The use of standardized willdlife strike rates, incorporation of risk metrics, and considerations of hazardous wildlife abundance data are potential sources of information that could be used within our framework.
Sunshine, Beaches, and Birds: Managing Raptor-Aircraft Collisions at Airports in Southern California
Wildlife-aircraft collisions (wildlife strikes) pose a serious safety risk to aircraft. Raptors (i.e., hawks and owls) are one of the most frequently struck guilds of birds within North America. Integrated wildlife damage management programs combine a variety of non-lethal and lethal management tools to reduce presence of raptors on airports. Live-capture and translocation away from an airport is a commonly used non-lethal method to reduce the risk of raptor-aircraft collisions. In southern California, USDA Wildlife Services airport biologists live-captured, marked with auxiliary markers (i.e., airport program-specific plastic leg band), and translocated approximately 1,232 raptors from seven airports and military bases located within the highly urbanized environment of the Los Angeles Basin during January of 2010-December of 2016. Ten different raptor species were marked and relocated during this effort. The composition of translocated raptors was red-tailed hawks (38.9%), Cooper’s hawks (27.5%), American kestrels (20.7%), barn owls (7.4%), and great horned owls (3.7%). Overall, the percentage of translocated raptors that returned to an airport was 11.1%. Although research is needed to better understand and increase the efficacy of such management efforts, this non-lethal method of reducing the presence of individual raptors at airports in southern California will be an important component of future wildlife management programs.
Belding’s ground squirrels (Urocitellus beldingi) cause extensive damage in alfalfa and other hay crops throughout substantial portions of the Intermountain West. Recent management efforts have largely focused on shooting, burrow fumigation, and occasionally grain baits. However, these tools are often either too costly to implement or ineffective. In 2015, the California Department of Pesticide Regulation approved a Special Local Needs permit to use zinc phosphide-coated cabbage for managing Belding’s ground squirrels in Siskiyou, Modoc, and Lassen Counties. This baiting strategy could provide a cost effective and efficacious management approach, although efficacy data were lacking. Therefore, we established a study to assess the importance of spatial variability of location sites, prebaiting, and ground squirrel density on efficacy of zinc phosphide-coated cabbage for Belding’s ground squirrel management across impacted hay-growing regions in northeastern CA. We also assessed potential differences in bait mixing strategies (in a tub via hand mixing vs. the use of a commercial-style cement mixer) on targeted zinc phosphide concentrations, as well as the degradation rate of zinc phosphide and moisture content of cabbage under environmental conditions. We did not detect a significant difference between hand and mechanical mixing. However, mechanical mixing was closer to the target level (mean = 101% vs. 115% for mechanical and hand mixing, respectively), was more precise, and allowed for the mixing of larger batches. As such, mechanical mixing was the strategy we used for field application. Furthermore, both moisture content (0.29% loss per hour) and zinc phosphide concentration (31% loss in 48 hours) steadily declined during a three-day observation period, indicating a fairly minimal window of exposure for nontarget species. See Baldwin et al. (2018) for additional details on lab testing of mixing methods and residual zinc phosphide levels associated with cabbage bait. During field trials, we found that prebaiting increased overall efficacy by approximately 18%, with efficacy 23% greater in the western (eastern Siskiyou and western Modoc Counties) vs. eastern portions (south-central Modoc County) of the study area. The tested bait was also substantially more efficacious when initial ground squirrel populations were larger, presumably due to a greater need for forage at high densities. Ground squirrel activity was relatively consistent throughout the day, although peaks were noted from 09:00 to 11:00 and from 13:00 to 15:00. Consumption of cabbage bait diminished throughout the day after initial application. Consumption was again high the following morning, but again diminished throughout the remainder of the day. Ideal times for bait application were likely before 09:00 and again before 13:00, although ground squirrels continued to feed on bait throughout the day. Zinc phosphide-coated cabbage bait appears to be an effective management option when prebaiting is used in Siskiyou County and in western portions of Modoc County. Additional research is needed to determine methods to increase efficacy in central and eastern Modoc County. See Baldwin et al. (2019) for additional details on this study.
California voles cause extensive damage to tree crops through girdling of young stems. Recent laboratory trials have indicated substantial repellency (up to 84%) of anthraquinone (a post-ingestive repellent) to voles on treated grain. Given these lab results, we established a field study to test the efficacy of anthraquinone applications to tree stems to reduce girdling damage from voles. We also assessed the impact of vegetation around the base of trees to determine the impact of cover on girdling activity. In Fresno County, CA, during summer 2016 and spring 2017, we established twenty 3.35 × 2.44-m bins (hereafter mesocosms) where we evenly spaced eight 1-yr-old clementine orange trees. Cover crops including various grasses and forbs were planted on randomly-selected halves of each mesocosm. All trees were treated with anthraquinone in half of the mesocosms; trees were left untreated in the remaining half. We captured 40 voles and released two individuals into each mesocosm and tracked girdling damage once weekly for five weeks during summer and six weeks during spring. We observed a significant reduction in girdling damage on anthraquinone-treated trees. The removal of vegetation around the base of trees completely eliminated girdling damage for anthraquinone-treated trees during summer, although vegetation did not significantly impact damage for untreated trees during summer, nor for either anthraquinone-treated or untreated trees during spring. We did not observe an increase in damage over time in anthraquinone-treated mesocosms, indicating that anthraquinone maintained its repellency during the duration of this study. Anthraquinone appears to be highly repellent to voles, and it is worthy of field study in other mammalian species as well.
Efficacy of IGI® Carbon Dioxide Gas to Kill Ground Squirrels and Pocket Gophers in Underground Burrows
Both ground squirrels and pocket gophers are significant pests in urban, rural, and agricultural settings within California. Various techniques are used to control these “pest rodents”; however, this presentation will explore the use of carbon dioxide (CO2) gas as a fumigant to control these rodents in their burrows. These studies were conducted to support efficacy submission requirements for the US Environmental Protection Agency (EPA) and selected state regulatory agencies in California, Washington, and Oregon. The Eliminator® System, Inert Gas Injection, LLC (IGI) was used for delivery of the carbon dioxide gas (cylinders) into underground burrows. Pre-treatment and post-treatment monitoring, visual counts, and burrow activity were used to determine the efficacy of the burrow fumigations. Carbon dioxide gas treatment of ground squirrel burrows resulted in 93.6-84.3% reduction in visual ground squirrels in the treatment plots 5-7 days after treatment, respectively, compared with untreated plots. CO2 gas treatment of ground squirrel burrows resulted in 71.5 ± 4.3% to 67.8± 4.3% reduction of reopened ground squirrel burrows in the treatment plots 1 and 5 days after treatment, respectively. In the pocket gopher trial, there was no evidence of tunneling or mound building in the treated test plots for 4 days after the last CO2 treatment, demonstrating 100% effect of the CO2 treatments against gophers with the Eliminator® System.
Piute ground squirrels, a subspecies of Townsends ground squirrels, are adapted to the Great Basin, which is characterized by extreme seasonal temperatures and highly variable precipitation that concentrates plant growth between February and July. Current available methods to manage ground squirrel populations in southern Utah were ineffective. We tested spot treating ground squirrel burrows with either Ditrac or Rozol, spot treatment of Ditrac compared to Rozol via bait stations, treating cabbage with zinc phosphide and baiting in fallow corners of irrigated agriculture, and spot treating with Rozol in early spring as possible methods to manage this subspecies of ground squirrel. Spot treating ground squirrel burrows with Ditrac and Rozol in early spring resulted in a decrease in the number of squirrels and active burrows counted. Spot treating with Ditrac and using Rozol bait stations in mid-spring did not result in a decrease in the number of squirrels and active burrows counted. Finally, using a 2% zinc phosphide solution baited with cabbage during the early summer resulted in a decrease in both squirrel numbers and active burrows, with minimal above-ground carcasses. Although early spring is not a common time to use grain-based bait, this method is effective at reducing ground squirrel numbers in alfalfa fields in Utah. Furthermore, using zinc phosphide is a possible new control method for Utah. Future research with larger sample size, in additional areas with this species is recommended.
Evaluating the Efficacy of the Rodenator™ (Propane-Oxygen Device) for Control of Black-tailed Prairie Dogs in Montana
Black-tailed prairie dogs’ feeding and burrowing behavior is a significant economic nuisance to agricultural producers. We tested the Rodenator™ on two portions of an isolated prairie dog town in Lewis and Clark County, Montana to determine how effective it was in reducing prairie dog numbers. Though other studies have been done using propane-oxygen devices, our study employed updated application techniques and an aggressive hole closing procedure to reduce the likelihood of false failures. In the southern area, we treated 53 burrows for 30 seconds with oxygen set at 40 psi and propane at 45 psi. In the northern area, we treated 120 burrows with an injection time of 45 seconds using the same oxygen and propane psi rates. Using the open burrow method for determining efficacy, our results were 58.7% for the southern area and 65% for the northern. Our study revealed that future studies should incorporate population surveys and appropriate control plots to determine the true efficacy of the Rodenator™, and we provide suggestions to improve overall method efficiency.
Additional methods and integrated strategies to reduce damage by voles and other small rodents are needed, especially where rodenticides cannot be readily used. This field study examined if fields vegetated with endophytic grasses (i.e., grasses infected with the fungi, Acremonium spp. or Neotyphodium spp.) which produce alkaloids that impair herbivory, resulted in lower abundance or impaired reproduction of small mammals. We also determined if small mammals inhabiting fields with endophytic grasses had impaired capabilities (i.e., smaller body size and body condition). A lower abundance of small mammals in fields of endophytic grasses was evident. However, there appeared to be very little difference in the size, body condition, and pregnancy rates of small mammals from either field type. These results suggested that endophytic varieties of grasses could be used reduce population numbers of rodents, thereby reducing human-wildlife conflicts resulting from overabundance of rodents.
Cage Efficacy Trials with Cholecalciferol Plus Diphacinone and Cholecalciferol Plus Brodifacoum Baits Using Richardson’s Ground Squirrels
There are many species of ground squirrels in North America and some species can cause substantial damage to agriculture and other resources. Traps and rodenticides are the most commonly used methods to reduce populations and damage. We tested the efficacy of three new formulations of rodenticides containing two active ingredients: cholecalciferol and diphacinone or cholecalciferol and brodifacoum using wild-caught Richardson’s ground squirrels. All three formulations had an efficacy of ≥60% and one cholecalciferol and brodifacoum formulation had an efficacy of 90%. Additionally, all formulations had lower concentrations of one or both active ingredients than commercial rodenticides that contain only one of the active ingredients. We also noted that squirrels that died generally consumed much more bait than those that survived. Most of these formulations had high efficacies in previous trials with voles and pocket gophers. We recommend that a field efficacy trial be conducted in a ground squirrel colony.
Can Barn Owls Help Control Rodents in Winegrape Vineyard Landscapes? A Review of Key Questions and Suggested Next Steps
Many winegrape farmers have installed nest boxes to attract barn owls to manage rodent pests, but this prospect has not been rigorously examined. We provide a brief history and context of the use of, and research on, barn owl nest boxes in California vineyards, and we suggest six key research questions necessary to better evaluate the capacity for barn owls to help control rodent pests: 1) How and where should boxes be placed to enhance barn owl occupancy? 2) How much are owls hunting in vineyards versus surrounding habitat? 3) How many rodents do they remove from vineyards? 4) Do they remove enough to meaningfully reduce rodent numbers and decrease crop damage? 5) What can farmers do to maximize hunting on their vineyards? and 6) What factors influence farmers’ decisions to use or not use nest boxes? Some work has recently been aimed at questions 1-3, but additional work is needed to confirm and generalize those results, and questions 4-6 remain, to date, unanswered. We suggest a research agenda to help address those unmet needs and advance our understanding of the potential for and application of barn owl nest boxes for pest management in winegrape vineyards.
Most raptor species rely on perches for hunting, resting, preening and roosting and in many agricultural areas the availability of adequate perches can limit raptor abundance and diversity. This has negative implications for both raptor conservation and the natural pest control services they can provide for farmers. Installing artificial perches on agricultural lands can therefore benefit both raptors and farmers. However, installing perches under current guidelines is difficult on California’s 38 million acres of rangelands, where rocky soil can be restrictive to anchoring poles belowground. We developed a novel method for modifying existing fenceposts to support raptor perches. These raptor perches are relatively light, easy to construct, can be transported in multiple pieces and assembled in the field. We installed 16 artificial raptor perches in four representative habitats on a California ranch to 1) determine if raptors will use artificial perches in each habitat; 2) test raptor preferences for different perch configurations; and 3) observe which raptor species utilize perches. Here, we share our perch design as well as our results from monitoring perches between August and November 2017. We found that American kestrels, great horned owls, barn owls, and red-tailed hawks utilized perches, as did a number of non-raptor species. Perch use by raptors was highest in an irrigated pasture and at a mid-elevation grassland site located on a hill. Perches at a low-elevation, unirrigated pasture with no slope and perches located in higher elevation oak woodland sites were used significantly less. In all habitats raptors preferred to utilize 15-foot perches over 20-foot perches. Raptors rarely utilized a lower perch when two were available on a single pole, suggesting that this added feature is not necessary to attract the species we observed.
Three Decades of Satisfied Israeli Farmers: Barn Owls (Tyto alba) as Biological Pest Control of Rodents
Compared to the use of invertebrate as biological pest control of agents of invertebrate pests, the use of vertebrates as biological pest control agents against other vertebrates is less common due to difficulties in manipulating and increasing their populations. Barn owls have been used as biological control agents in different countries, including Israel, which initiated the project in 1982 and as of 2017 has a total of 3,250 nest boxes deployed in the country. Our aim here was to determine whether farmer satisfaction/dissatisfaction response to a survey on the effectiveness of the barn owl project is related to the number of nest boxes and breeding barn owl pairs that the farmers have in their fields; and whether farmers deploy nest boxes as a result of previous rodent damage in their fields. We found that farmers that had incurred rodent damage both used more rodenticides and also installed more nest-boxes (and consequently had more breeding barn owls) than those who reported a lack of damage. Farmers who were satisfied using barn owls had more nest boxes and hence more breeding barn owls, and reported that rodent damage had decreased during the project, as compared to farmers who were not satisfied with the project. The number of nest boxes added to agricultural fields is growing yearly, both due to scientific and national projects and because farmers in Israel purchase nest boxes independently, indicating their belief in the project.
Animal intrusion causes significant agricultural losses each year. Wild and domestic animals destroy crops by eating and trampling them, and can pose food safety risks due to the deposition of feces on or near the crops. Birds are one of the most challenging animals to keep out of agricultural fields. Growers try countless methods to deter them, including visual, auditory, tactile, and olfactory means. While some of these methods work some of the time, none provide stand-alone protection all the time. Recently there has been interest in developing technology-based solutions to deter nuisance birds in agricultural settings, while others are exploring more natural methods, including falconry. We provide a general overview of bird deterrent methods that are currently in use in agricultural settings, and explore options for novel methods. We found that very few independent scientific studies have been conducted to assess the efficacy of most bird deterrent methods. Ultimately, a multi-tiered approach using integrated pest management techniques will likely be most useful as it can be tailored to meet the needs of individual farmers.
In order to potentially reduce use of environmentally damaging rodenticides, integrated Pest Management (IPM) for rodents, or Ecologically Based Rodent Management (EBRM), proposes a more sustainable management approach using strategies informed by an increased understanding of rodent population and community ecology, including interactions with important predators, such as raptors. Nest boxes and perches can encourage raptor presence in agricultural areas and potentially enhance the regulatory ecosystem services provided by raptor predation of agricultural pests. To assess this idea, we studied American kestrels (widespread, generalist predators that readily use nest boxes) in a fruit-growing region of northwestern Michigan. The most common mammal prey in the diets of these kestrels from 2013 through 2016 were voles, which are considered the most important rodent pests in temperate fruit orchards. We utilized live trapping to measure small mammal abundances and activity during the summer at sites with and without active kestrel nest boxes; furthermore, we utilized camera trapping to measure small mammal presence during the winter, when damage to trees is most likely. As predicted, small mammal abundance and activity was lower at orchards with active kestrel boxes and at orchards that had been more recently mowed; however, these differences did not carry over as differences in winter presence in orchards. Our sampling demonstrated that voles were absent from orchards during both summer and winter, which suggests that orchards offer insufficient cover except under certain conditions, such as sustained snow cover. Instead, mice were the most abundant small mammals in most orchards during the summer and were also present during the winter. More evidence is therefore needed to determine the extent of orchard damage attributable to Peromyscus spp. and whether indirect effects of kestrels on Peromyscus spp. may reduce damage. We provide recommendations for future research on the effects of raptor predation in orchards.
Depredation by common ravens often exceeds stakeholders’ levels of acceptance. Common sources of excessive raven damage include loss of young livestock and nest depredation of species of concern, such as desert tortoise, greater sage-grouse, and least tern. USDA/APHIS Wildlife Services applies the avicide DRC-1339 (3-chloro-p-toluidine hydrochloride, CPTH) formulated in an intact-boiled egg bait to reduce such damage under the DRC-1339 Concentrate Livestock, Nest & Fodder Depredations label (EPA No. 56228-29). Although considered extremely effective on corvids, DRC-1339 is a slow acting toxicant and ravens may succumb away from the bait site, preventing the use of carcass recovery as a means to estimate take. To estimate take, Wildlife Services employs a model comprised of a bioenergetics module to predict consumption combined with a toxicological module that predicts mortality based on a probit analysis. This model has recently been revised to improve and standardize take estimates for common raven management activities using the egg baits covered by this label. Common ravens exhibit complex behaviors that impact the amount of bait consumed when offered DRC-1339 egg baits. The approaches to capturing this behavior in the model are presented along with take estimates associated with a range of baiting scenarios.
What Do We Need to Know to Assess Individual and Population-level Effects on Wildlife from Anticoagulant Rodenticides?
Anticoagulant rodenticides have been detected in many species of wildlife worldwide; yet the origins, exposure pathways, and effects of this exposure are not well understood. Furthermore, to accurately characterize the risks from rodenticide use, information is needed on what proportion of populations are being exposed, what proportion of the exposed individuals are affected, and in what ways. The relationship between anticoagulant rodenticide concentrations found in wildlife and the rate of mortality or illness is the subject of much current research. Residue levels observed in liver and whole body analyses vary, and overlap extensively among apparently healthy asymptomatic individuals and sublethal and lethal cases. Results from laboratory studies also show there can be wide variability in lethal and sublethal effects among and within taxonomic groups. Correlating the sublethal and reproductive effects observed in laboratory studies with realistic exposure scenarios and effects in the wild is needed to improve risk assessments. For species with limited numbers/declining populations, a critical question is whether the rodenticide exposure documented in individual animals inhibit population growth or contribute to population declines by lowering survival and reproductive success. This information is essential to the regulatory agencies that must weigh the risks and benefits of rodenticide uses and identify restrictions that are effective in reducing risks to wildlife. A primary objective of this symposium was to facilitate communication between regulators and researchers. Current research on many of these topics was presented, and was followed by discussions on how to improve our understanding of what factors lead to wildlife exposure and improve our ability to assess the effects of exposure on individuals and populations. A collaborative approach will be developed to design studies that provide regulatory and wildlife management agencies with additional science on which to base their decisions.
Anticoagulant rodenticides (ARs) are used to control rodents around homes, buildings, and in agriculture. They have been found widely in predatory and scavenging wildlife as a result of secondary exposure and less commonly in herbivores and omnivores from primary exposure. While predators and scavengers have been monitored for AR exposure, very little information is available about AR residues in edible muscle tissue of game animals. Game animals may be exposed to ARs through direct consumption of bait, ingestion of contaminated food or vegetation, or consumption of contaminated prey items. Carcasses of three species of game animals (black bear, wild pigs, and mule deer) were collected opportunistically for this study from 2013 to 2015. Causes of death were mainly depredation, vehicular trauma, or hunter harvest. Sampling was performed in the field by California Department of Fish and Wildlife and US Department of Agriculture Wildlife Services staff. Tissues were analyzed for 37 deer in 11 counties, 120 wild pigs in 10 counties, and 12 bears in eight counties. The highest prevalence of AR exposure was found in bears, with 83% of tested livers containing ARs. Bear were most likely to be exposed to brodifacoum, a second generation AR used primarily in and around residences. Prevalence of exposure in wild pigs was 8.3%. Pigs were most likely to be exposed to chlorophacinone, used primarily in agriculture. More than half of pigs with AR residues in their liver also had AR residues in their muscle tissue. There were no AR detections in muscle samples tested for bears with AR residues in liver. None of the deer livers tested positive for ARs.
A seminal question in wildlife toxicology is whether exposure to an environmental contaminant, in particular a second-generation anticoagulant rodenticide, can evoke subtle long lasting effects on body condition, physiological function and survival. Many reports indicate that non-target predators often carry residues of several rodenticides, which is indicative of multiple exposures. An often-cited study in laboratory rats demonstrated that exposure to the second-generation anticoagulant rodenticide brodifacoum prolongs blood clotting time for a few days, but weeks later when rats were re-exposed to the first-generation anticoagulant rodenticide warfarin, coagulopathy was more pronounced in brodifacoum-treated rats than naïve rats exposed to warfarin. To further investigate this phenomenon, American kestrels were fed environmentally realistic doses of chlorophacinone or brodifacoum for a week, and following a week-long recovery period, birds were then challenged with a low-level dietary dose of chlorophacinone. In the present study, neither hematocrit nor clotting time (prothrombin time, Russell’s viper venom time) were differentially affected in sequentially exposed kestrels compared to naïve birds fed low-level dietary dose of chlorophacinone. While the present findings do not reveal lasting effects of anticoagulant exposure on blood clotting ability, findings in laboratory rats and other species have demonstrated such effects on blood clotting, and even other molecular pathways associated with immune function and xenobiotic metabolism. Additional studies using an environmentally realistic route of exposure and dose are underway to further test this hypothesis.
Prevalence of First and Second-generation Anticoagulant Rodenticide Exposure in California Mountain Lions (Puma concolor)
In 2016, the Wildlife Investigations Lab initiated a statewide mountain lion health surveillance study to understand population health and anticoagulant rodenticide (AR) exposure. Exposure to first-generation (FGARs) and second-generation (SGARs) anticoagulant rodenticides are common in predators such as raptors, wild canids (i.e., foxes and coyotes) and bobcats. However, statewide data regarding rodenticide exposure in these species, including mountain lions, have been limited. Our objectives were to determine the statewide prevalence and geographic distribution of AR exposure in necropsied mountain lions. We used liquid chromatography/mass spectroscopy to detect rodenticides in liver samples from 111 (77 male: 34 female) mountain lion carcasses from 37 counties that died between Feb 2016 and Feb 2017. Necropsied carcasses were lions taken on depredation permits, vehicular strike, public safety, or other reasons. Overall, we detected ARs from the liver tissue of mountain lions from 35 counties with 105 of the 111 (94.5%) lions having exposure. We detected FGARs in 81 individuals (73%) from 33 counties and SGARs in 102 individuals (92%) from 35 counties. Seventy-eight individuals (70%) were exposed to both SGARs and FGARs while 6 (5%) individuals had no detectable AR concentration. Of the FGARs detected, diphacinone was the most common and was observed in 67% of sampled individuals. Brodifacoum was the most common SGAR, detected in 90% of sampled individuals. Exposure to FGARs was correlated with exposure to SGARs (χ2 = 5.8, p = 0.01). Exposure to ARs was not associated with lower body condition score. Although our study represents only one year of data, we demonstrate that exposure to both FGARs and SGARs is widespread in California’s mountain lions. We recommend continued AR screening of livers from mountain lion carcasses to further enhance our understanding about the relative contributions they may have on population health. Continued monitoring would also measure the effectiveness of regulatory changes intended to reduce non-target wildlife exposure to rodenticides
Widespread Anticoagulant Poison Exposure is Linked with Immune Dysregulation and Severe Notoedric Mange in Urban Bobcats
Human activities threaten wildlife with a variety of novel stressors such as exposure to toxicants. Anticoagulant rodenticides (ARs) are toxicants applied worldwide and through bioaccumulation, threaten species that prey on poisoned rodents or their predators. We studied a population of urban bobcats in southern California that declined rapidly from 2002-2005 due to notoedric mange. We first assessed prevalence of AR exposure using blood and liver samples across the population and found widespread exposure (>90%). Death associated with mange was strongly correlated with cumulative first- and second-generation AR exposure. These findings suggested that exposure to both first- and second-generation ARs were an underlying cause of the disease. We next aimed to understand the sublethal immunological and physiological effects of AR exposure in this natural population. We used two approaches: 1) we used a comprehensive suite of health assays (complete blood counts, blood chemistry assessment, and immunological profiling), and 2) we quantified AR-induced differential gene expression in blood for a subset of individuals. We found that sublethal AR exposure, primarily measured as exposure to diphacinone, is associated with hallmark indicators of generalized systemic inflammation that in persistence could promote immune dysfunction. Further, differential gene expression findings supported the results of immunological profiling. Further, a decrease in the expression of genes associated with epithelial maintenance simultaneous to a decrease in gene expression linked with ectoparasitic immune response may explain the link between AR exposure and mange vulnerability. Such indirect effects of sublethal exposure exemplify the challenge of protecting wild populations from common toxicants in human-dominated environments.
Monitoring anticoagulant rodenticide (AR) exposures in birds of prey presented to a wildlife clinic or rehabilitation setting has several advantages and disadvantages. Advantages include the ability to document signs of toxicosis in live birds. Additionally, in birds that die due to AR toxicosis, post-mortem lesions in the non-frozen, non-autolyzed cadaver will illustrate patterns of AR-induced hemorrhage. In birds that die or are euthanized due to other causes, liver samples can be collected and analyzed for AR residues. Disadvantages include an inability to ascertain the dose of AR ingested. In birds with exposure to multiple ARs, the timing of ingestion is also unknown. The route of exposure and pathway through the food chain likewise are unknown. Importantly, determining the true incidence of toxicosis and mortality among the sampled birds is not possible because birds that are found and transported for care may not be reflective of mortalities in the overall population. Despite the limitations of this method of sampling, much useful information can be gathered, particularly in studies that are continued over time. Two such monitoring studies conducted in Massachusetts, USA over a ten-year period, showing widespread exposure among sampled birds, will be discussed. In addition, other information that is needed to enhance the data obtained by cadaver sampling will be highlighted, particularly as these data gaps relate to evaluation of mitigation efforts.
In recent years, anticoagulant rodenticides have emerged as an important factor reducing the survival of many birds of prey and some predatory mammals (Berny and Gaillet 2008, Jacquot et al. 2013, Poessel et al. 2015, Serieys et al. 2015, Murray 2017). Understanding the ecological factors driving the exposure of predators is a key component in assessing the risk posed by anticoagulant rodenticides. We have reviewed the literature to better understand and synthesize the ecological factors driving AR exposure in predators, focusing on landscape and environmental management, traits of the exposed predators and the most common exposure pathways. On a global scale, the large output of ARs, in particular the more toxic and persistent second generation ARs into urban and agricultural settings and the relatively large footprint of these landscapes, has led to widespread AR exposure of many species, ranging from insects to large carnivores (Dowding et al. 2010, Sánchez-Barbudo et al. 2012, Serieys et al. 2015, Alomar et al. 2018). The methods of applying ARs vary widely, and can range from fastening bait stations to the outside or inside perimeter of buildings, to placing AR bait in underground burrows in fields, to mass application of ARs in agricultural fields and orchards (Corrigan 2001, Rattner et al. 2014). The scale of AR field application varies from a couple of hectares to mass application of ARs on a regional scale (3,000 - 10,000 km²) to control rodent outbreaks (Jacquot et al. 2013, Baldwin et al. 2014). General inferences can be made with regards to the traits of the most affected predators. We determined that at-risk predators tend to be nocturnal opportunistic predators for which rodents are a key dietary component, seasonally or year-round (Birks 1998, Jacquot et al. 2013, Hindmarch and Elliott 2015, Serieys et al. 2015). They also tend to be non-migratory and occupy habitats within, or in close proximity to landscapes that are heavily influenced by human activities such as intensive agriculture or urban areas (Birks 1998, Way et al. 2006, Elmeros et al. 2011, Christensen et al. 2012, Cypher et al. 2014, Nogeire et al. 2015, Poessel et al. 2015, Serieys et al. 2015, Hindmarch et al. 2017). Predators that consume rats in urban environments are disproportionately affected by ARs (Lambert et al. 1981, Hindmarch and Elliott 2014, 2015). As our understanding of how ARs are transferred up the food-chain is still limited, there is a need to further comprehend the extent to which non-target prey are being exposed to ARs in different landscapes, as we are frequently documenting AR residues in predators that do not typically prey on rodents (Dowding et al. 2010, Ruiz-Suárez et al. 2014, López-Perea et al. 2015). We recommend a focus on urban landscapes, where to date no exposure data has been collected on non-target prey. We also have a very limited understanding of non-target prey exposure in the urban-wildland/agricultural interface where opportunistic predators are known to hunt both habitat types interchangeably. Finally, we need to decipher whether the mounting evidence of exposure in predators translates into any sub-lethal and population levels effects. For a more in-depth review of this topic, we refer to the chapter “Ecological Factors Driving Uptake of Anticoagulant Rodenticides in Wildlife" (Hindmarch and Elliott 2018) in the book Anticoagulant Rodenticides and Wildlife (van den Brink et al. 2018).
Recent studies have correlated anticoagulant rodenticide exposure to the development of mange in wild felids. However, a causative association between anticoagulant exposure and the onset of mange or immune dysfunction that may increase susceptibility of wild felids to manage has not been established. To investigate the potential connection between anticoagulant rodenticide exposure and immune dysfunction, specific-pathogen-free domestic cats were exposed to brodifacoum over a six-week period and vaccinated with irrelevant antigens at different points during the course of the experiment to assess recall and direct immune responses. Measures of immune response included delayed-type hypersensitivity tests and cell proliferation assays. IgE and antigen-specific antibodies were quantified via ELISA assays. No cats developed coagulopathies despite having detectable levels of brodifacoum in the blood. Brodifacoum cats had significant decreases in the production of certain cytokines including IL-6 and IL-4. The results of this study suggest that cats may be less susceptible to anticoagulant rodenticide induced coagulopathy and that the effects of environmentally realistic brodifacoum exposure on humoral and cell-mediated immunity against foreign antigen exposures in domestic cats are minimal.
Incident data can support risk assessments by providing evidence of adverse effects of rodenticides to birds following operational applications. Traditionally, field monitoring for rodenticide incidents has focused primarily on raptors. However, non-raptor birds may also be poisoned (rodenticide exposure resulting in adverse effects including mortality) by rodenticides through consumption of the rodenticide bait and contaminated prey. I conducted a literature search canvassing 12 government and scholarly databases for rodenticide incidents (evidence of exposure to a rodenticide, adverse effects, or exposure to placebo baits) involving non-raptor birds. I used the search terms ‘rodenticide’ and ‘birds’ and from these results, I excluded entries of raptor incidents, laboratory toxicology studies, duplicate records, and unpublished literature (except for entries in the US Environmental Protection Agency’s Incident Data System). I ended up with 641 non-raptor rodenticide incident records spanning the years 1931 to 2016. The incident records included 17 orders, 58 families, and 190 non-raptor bird species ranging from emus (Dromaius novaehollandiae) to songbirds (Order Passeriformes). Nineteen anticoagulant and non- anticoagulant rodenticide active ingredients were associated with the incidents. Rodenticide formulations including bait blocks, cereal based pellets, carrot baits, pastes and jams, liquids, and loose grain baits following above-ground, below-ground, in-bait stations, and in-meat applications have results in non-raptor incidents either through direct ingestion of the rodenticide or via contaminated invertebrate and vertebrate prey. The availability of incident records affected the numbers of incidents in this review. The availability is in turn is affected by the infrastructure for monitoring and reporting incidents. For example, although rodenticides are used worldwide, I found non-raptor incident records from only 15 countries. I compared the number of incidents and species detected by surveillance method (passive vs. active surveillance) and by the purpose of application (for ecological restoration vs for human welfare). More incidents were reported from passive surveillance and following applications for human welfare but a significantly greater number of species were detected in proportion to the number of incidents found through active surveillance and following applications for ecological restoration. In conclusion:1) A broad diversity of non-raptor species are affected by rodenticides with a variety of modes of action, formulations, and application methods; 2) Surveillance method and the purpose of application can influence the quantity and quality of incident data; 3) The lack of evidence does not imply the lack of hazard but signifies poor infrastructure for monitoring and reporting non-raptor avian incidents; 4) Awareness of the breadth of species diversity of non-raptor bird poisonings from rodenticides may increase the incentive for monitoring and reporting them and this in turn can strengthen the predictions of harm characterized by risk assessments.
Stoats are a major predator of endemic forest-dwelling bird species in New Zealand and are responsible for several local extinctions. Thus, their eradication is key for biodiversity conservation. However, sustained control of stoats is required on islands within an impressive swimming distance of the mainland. Our objective here was to test the use of toxicant-free, automatic traps as a sole means of stoat control on a near-shore island with very high reinvasion potential. We installed a grid of Goodnature® A24 self-resetting traps on Great Island, part of a World Heritage site within Fiordland National Park on the South Island of New Zealand, in October 2016 and undertook pre-feeding and monitoring through March 2017, when traps were set. Within four weeks of setting traps, tracking indices for stoats decreased from 95% to 5% and have so far remained at or near effectively 0% throughout the ongoing project.
The value of thermal imagery has been well documented for use in many aspects of wildlife damage management and other animal identification purposes. As technology has improved, prices for these devices continue to become more affordable. Two thermal imaging cameras were evaluated to determine effectiveness and utility of the devices under environments potentially encountered in the field. We tested the FLIR One (FLIR ONE) for an iPhone smart phone, and the FLIR Scout TK Compact Monocular (FLIR TK) device. Photographs of domestic animals and wildlife species were collected at distances of 3m-50m. A survey was developed and administered to professionals working with wildlife or domestic animals, containing paired images for each camera taken from similar distances and color palette. Survey participants (n = 52) reported the FLIR ONE camera produced more favorable images at closer distances (P < 0.05), and the FLIR TK at longer distances (P < 0.05). Overall, participants preferred (P < 0.05) the FLIR TK for producing the most desirable or useful images. Results of this study suggest both the FLIR TK and FLIR one thermal imaging cameras have the potential to be useful in collecting images of animals under low light conditions.
Lethal rodenticides and other lethal tools of managing commensal rodent populations long-term are not sustainable due to population rebounds and increasing resistance to rodenticides. The use of integrated pest management (IPM) programs are more prevalent due to consumer desire to decrease rodenticide use and utilize environmentally friendly, humane methods. IPM plans often require multiple tools to control an infestation, such as physical, biological and chemical measures. Here, we propose that rodent population management would benefit from a new tool aimed at targeting the biological source of overabundance: reproduction. SenesTech, Inc. (Flagstaff, AZ USA) has developed ContraPest®, a liquid bait that limits the reproductive capacity of both male and female wild Norway and Roof rats. The two active ingredients, 4-vinylcyclohexene diepoxide (VCD) and triptolide, deplete all stages of follicles in the female and disrupt spermatogenesis in the male. Laboratory and field studies reveal that ContraPest® is palatable and repeatedly consumed by rats even when provided with ad libitum food and water. Studies involving laboratory and wild caught rats have demonstrated a 93 - 100% reduction in litter sizes of rats treated with ContraPest® compared to control rats. ContraPest® was tested on free ranging rat populations in agricultural and urban settings. Rat populations on protein production farms decreased by an average of 46% following 100 days of treatment with ContraPest®. In a complex urban environment, where property boundaries limit access to populations and foraging areas, ContraPest® reduced the seasonal population peak by 67% after 133 days of baiting. These studies, combined with all of our field studies and population reduction models, demonstrate that ContraPest® is a highly effective rodent contraceptive bait in a variety of environments. We strongly believe that adding/implementing fertility management via ContraPest® to an IPM program would enhance long-term rodent population control in rural, urban, and agricultural environments.
Non-Trapping, Non-Invasive, Rapid Surveillance Sampling Using Tracking Tunnels, Trail Cameras, and eDNA to Determine Presence of Pest Predator Species
A common challenge for land managers is knowing which vertebrate pest species are present in areas they manage, especially if such areas are remote like isolated habitats, rugged terrain, or infrequently traveled islands. Most invasive predator species, such as feral dogs, cats, mongoose, and commensal rodents pose great threat to human health and key resources such as native species. Animal trapping to determine the presence of a pest species can be expensive and dangerous, requiring permits, experienced personnel, multiple days, and multiple trapping methods. Furthermore, many invasive pest species may go unnoticed because they are nocturnal, secretive, or leave little evidence of their presence. Tracking tunnels, trail cameras, and environmental DNA (eDNA) are non-trapping methods that can be used to rapidly assess if vertebrate pest species are present in a given habitat or ecosystem, including before, during, and after pest suppression techniques are implemented. We share tracking tunnel dimensions and specifications so readers can make their own tracking tunnels for rodent and other small mammal sampling, and we provide some common distributers where tracking tunnels can be purchased. A brief overview of trail camera technology and eDNA forensic uses are described, as well as their applications for vertebrate pest identification, surveillance, and damage management. To demonstrate these methods, we share example case studies from the Caribbean, including first time records of house mouse presence at Sandy Point National Wildlife Refuge in St. Croix (US Virgin Islands) and along a rainforest elevation gradient in the Luquillo National Forest, Puerto Rico. Additionally, we describe case studies of trail camera use on Desecheo Island (Puerto Rico) to determine brodifacoum bait consumption, and eDNA use in Wyoming to determine native bird depredation events. Tracking tunnels and trail cameras are recommended as quick and inexpensive ways to reveal the vertebrate pest species that are present at a site or habitat. These non-trapping, non-invasive techniques can provide quick and efficient methods of surveillance, detection, and monitoring of vertebrate pests, and otherwise may be used as effective tools to aid in wildlife damage management.
Mice in homes leave droppings and urine and are vectors for Hanta virus and Lyme’s disease. This study tested whether ultrasounds from a TRANSONIC PRO, Bird-X Inc. Chicago Il., (hereafter T-PRO) significantly reduced mouse problems in an old farm house. One T-PRO was used on “quiet volume” (frequency range 20 kHz-45 kHz at 72 - 78 dB @ 0.5 m) for all tests. Three paired tests were conducted, one pair for identical periods of autumn for 2009 and 2010, two for full year cycles 2012 to 2013, 2013 to 2014, 2015 to 2016, and 2016 to 2017. Efficacy was assessed using indirect evidence of ultrasound detection/avoidance by mice based on absence of mice trapped in the house or droppings counted on kitchen counters during test periods when the T-PRO was “ON” versus similar counts when the T-PRO was “OFF.” Mice were free to leave the areas of the sounds and the house entirely, and thus failed to evidence habituation. In all years six peanut butter baited Victor brand snap traps were kept on the top three basement steps below the 2.5-m × 1.1-m entrance hall extending from the exterior door to an inner hall door. The latter was kept closed, but had a 1-cm gap under it that permitted mice to enter the kitchen area. In the three test periods when the T-PRO ultrasonic sounds were being broadcast, nine mice were caught and 14 droppings found on the kitchen counter; versus 91 mice caught and 154 droppings counted when the T-PRO was turned “OFF.” A two tailed T-Test indicated a P = 0.0007, T = 9.2998 df = 4, with a mean of 30.33 mice caught/test cycle with the unit “OFF” versus a mean of 3.67/cycle when it was “ON.” No changes were made in house/hallway during this study. Seasons tested matched precisely for multiple years reducing probability that annual variations in mouse populations near the house might have caused random spikes in mouse numbers trapped. Snap traps and the T-PRO presented an effective integrated pest management system resulting in a nearly mouse-free house.
Population Density and Home Range Estimates of Black Rat (Rattus rattus) Populations in Southwestern Puerto Rico
Black rats are among the world’s most invasive rodent species and are responsible for considerable agricultural losses and risks to human health through zoonotic disease. In Puerto Rico, rats may also compete with the primary rabies reservoir (the small Indian mongoose) for baits during oral rabies vaccination (ORV) programs. We evaluated black rat population density and home range size on the Cabo Rojo National Wildlife Refuge, southwestern Puerto Rico. We fitted 10 rats with VHF transmitters and tracked them using radio telemetry for approximately 4 weeks. We entered locations into ArcGIS and obtained minimum convex polygon (MCP) home range estimates. We established two plots of 55 snap traps and performed removal for 5 consecutive days during January and July, to correspond roughly with wet and dry seasons for this region. To calculate abundance, we entered snap trap data using a removal model approach in Program MARK. We calculated the effective trapping area by creating a buffer around the trapping area based on the square root of mean home range estimate. We divided the abundance calculated in MARK by the effective trapping area to calculate the estimated population density. Mean MCP home range estimate was 0.28 ha (SE: 0.05, range: 0.07-0.50 ha). Population density estimates were 114.7 (SE: 201.80) and 19.3 (SE: 6.85) per ha for January and July, respectively. To reduce the potential for rat consumption of ORV baits, wildlife managers should consider conducting ORV activities in Puerto Rico during periods of lower rat abundance or density.
Rat lungworm (Angiostrongylus cantonensis) is a zoonotic nematode that causes rat lungworm disease (angiostrongyliasis), a potentially debilitating form of meningitis, in humans worldwide. The definitive hosts for rat lungworm are members of the genus Rattus, with gastropods as intermediate hosts. This parasite has emerged as an important public health concern in the U.S., especially in Hawai‘i, where the number of human cases has increased in the last decade. Here we discuss the current knowledge of the rat lungworm, including information on the life cycle and host species, as well as updates on known infection levels. Three species of rat have been unintentionally introduced and become established in Hawai‘i, all of which have been documented as definitive hosts of rat lungworm. Our recent findings indicate that infection levels in rats can vary by species and age. Based on these findings, we also suggest the possibility that R. rattus populations in Hawai‘i are capable of developing some form of acquired immunity to infection over time, which could have important management implications related to control operations. Information on rat lungworm infection levels and distribution in Hawai‘i is lacking, especially in rat definitive hosts, and the USDA National Wildlife Research Center and the University of Hawai‘i at Hilo are continuing efforts to help fills these gaps in knowledge.
Nutria, a semi-aquatic, South American rodent, was introduced to Maryland during the early 1940s. Originally brought to the area for fur farms, the market never established and animals were released or escaped. Nutria thrived, destroying coastal wetlands which resulted in negative environmental and economic impacts to the Chesapeake Bay region. To preserve and protect valuable wetland resources, the Chesapeake Bay Nutria Eradication Project (CBNEP) was established in 2002 through a partnership between the United States Fish and Wildlife Service, the United States Department of Agriculture’s Wildlife Services, Maryland Department of Natural Resources, and many state agencies and non-governmental organizations. Since inception, the CBNEP has removed and reduced nutria populations to near zero across ¼ million acres of wetlands throughout the Delmarva Peninsula (Maryland, Delaware, and Virginia). The CBNEP has aided in the protection of critical natural resources and provided assistance to over 400 private landowners. Throughout its history, the CBNEP has developed new detection techniques and modified existing methods as the nature of the eradication effort changed. We provide a project overview and detail several observer-based and device-based methods that were developed and used for detection of nutria including: shoreline and ground surveys, monitoring platforms, detector dogs, lure development and remote triggered cameras.
Fumigation of Burrowing Rodents with Carbon Monoxide: A Comparison to Alternative Management Options
Pocket gophers and ground squirrels cause extensive damage to many crops. Pressurized exhaust injection devices are increasingly used for managing these rodents, although no data were available to support their use. Therefore, we established a study to: 1) determine the efficacy of pressurized exhaust machines for pocket gopher and ground squirrel management, 2) compare these results to other burrow fumigant options, and 3) compare their cost effectiveness. Specifically, we tested two different pressurized exhaust machines for both ground squirrels and pocket gophers: Pressurized Exhaust Rodent Controller (PERC), and 2) Cheetah rodent control machine. For California ground squirrels, efficacy for the PERC machine was greater in moist soils (mean = 100%) than in drier soils (mean = 66%). Initial treatments using the PERC machine were more expensive than other burrow fumigation options, given the large cost of the machine. However, costs quickly dropped below that of gas cartridges (~44 days), and eventually dropped below that of aluminum phosphide if used extensively (~830 days). Efficacy for the Cheetah rodent control machine was far less encouraging for California ground squirrels, with results showing increased squirrel numbers at treatment sites (mean = +115%) post-treatment. For pocket gophers, aluminum phosphide (mean = 86%) and trapping (mean = 81%) proved to be more effective than PERC applications (mean = 56%) in heavy organic soils. We observed somewhat greater PERC efficacy in mineral soils (mean = 68%), suggesting potential variability in efficacy across soil types. At this point, the use of the PERC machine appears to be a viable option for inclusion into Integrated Pest Management programs for burrowing rodents where alternative options are limited; the Cheetah rodent control machine showed no utility for ground squirrel management in our study. More extensive testing of pressurized exhaust devices in differing soil types and under variable moisture levels is needed to determine their utility across a broader spectrum of treatment situations.
The Relative Importance of Different Trophic Pathways for Secondary Exposure to Anticoagulant Rodenticides
Secondary exposure of predators to anticoagulant rodenticides, and in particular second generation anticoagulant rodenticides (SGARs), is a global phenomenon. The widespread and large-scale nature of this exposure has attracted considerable concern, although the consequences in terms of likelihood of poisoning of individuals and resultant impacts on populations are not well characterised. Secondary exposure of predators may as rise from once or more of: (i) eating contaminated commensal rodents subject to control (target species are typically rats and house mice); (ii) consumption of contaminated non-target small mammals (such as Peromyscus, Microtus, and Apodemus species) that encounter and feed on what are rodent-attractive baits; (iii) consumption of non-rodent vertebrate and invertebrate prey that may also incidentally encounter and eat baits. We hypothesised that predators feeding primarily on target species may be most at risk of exposure to SGARs while those predominantly taking non-mammalian prey may be at least risk. We tested this hypothesis by comparing exposure, determined from the presence and magnitude of SGAR liver residues, in red kites (Milvus milvus), which feeds extensively on rats, in barn owls (Tyto alba), kestrels (Falco tinnunculus), and tawny owls (Strix aluco) that feed widely on non-target small mammals, and in sparrowhawks (Accipiter nisus) that feed predominantly on small birds. We found that the scale and magnitude of exposure was broadly consistent with our hypothesis, and that controlling for age in the analysis could be important as older birds can accumulate residues with age. However, exposure in kestrels was typically greater than that in barn owls and tawny owls, despite what is thought to be a general similarity among the species in their diets. We discuss the relative importance of trophic pathways relative to other factors that may drive secondary exposure in predators, and confirm that species that feed on rats or other target species may be at most risk of exposure and poisoning.
Fleas are remarkable and highly specialized insects, with no part of their external anatomy being easily mistaken for that of any other insect. Due to their small size, the subtle differences among the distinguishing morphological characteristics of each species, and complexities of preparing specimens, identifying, and working with fleas is challenging. Various documents and taxonomic keys are available that discuss mounting procedures and the identification of medically important fleas for large regions of the world including the United States; however, many of these have become antiquated over time. Some of the distinguishing specialized characteristics exhibited among flea species, as presented in older keys, come in the form of line drawings, which are accurate but can be difficult to use when comparing it to structures on a whole specimen when viewed through a microscope. This paper presents a guide which describes in detail previously developed, but obscure techniques covering the preservation, preparation, clearing, and mounting of Siphonaptera specimens. In addition, we are also presenting an easy-to-use photographic key of twelve flea species collected from back yard wildlife, as well as pet cats and dogs in Orange County, CA. This key, which is freely available online at the Orange County Mosquito and Vector Control District’s website, is an effective tool for the identification of common flea species found in southern California. Using the key in conjunction with the mounting guide will provide users with a full-circle guide to preserving, identifying, and mounting flea specimens. Keyed flea genera include Cediopsylla, Ctenocephalides, Diamanus, Echidinophaga, Hoplopsyllus, Leptopsylla, Nosopsyllus, Orchopoeas, Pulex, and Xenopsylla. Examined hosts include cats, coyotes, dogs, mice, opossums, rabbits, raccoons, rats, skunks, squirrels, and woodrats.