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Open Access Publications from the University of California


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:

Marsh, Rex E.  2008.  A History of the Vertebrate Pest Conference.  Proc. Vertebr. Pest Conf. 23:310-326.

Gorenzel, W. Paul.  2004.  Opening Remarks - A Retrospective Look at the Vertebrate Pest Conference.  Proc. Vertebr. Pest Conf. 21:1-2.

Howard, Walter E.  1982.  Twentieth Anniversary of Vertebrate Pest Conferences in California.  Proc. Vertebr. Pest Conf. 10:235-236.

Howard, Walter E.  1962.  Opening Remarks – Vertebrate Pest Control.  Proc. Vertebr. Pest Conf. 1:1-7.


Developing Alternatives to Protect Domestic Sheep from Predation in South Africa

South Africa has approximately 8,000 commercial small livestock farms and 5,800 communal/subsistence farmers throughout the country. Reported rates of small livestock loss to predation range from 3-13% and 0.5-19% from communal farming areas. A range of predators exist on the African continent, but in southern Africa major livestock losses are primarily due to black-backed jackal and caracal. South Africans have been managing caracals and jackals for over 300 years with no elimination of predation. During the aforementioned time frame, producers have used and/or developed a number of techniques including lethal, nonlethal, and integrated predator damage management to address predation losses. In the Karoo area of South Africa, one producer decided that a new way needs to be developed after losing over 60 lambs in a month, while practicing continuous removal of caracal and black-backed jackal. His integrated predator damage management system includes using a prototype nonlethal collar system for sheep and lambs. The collars are used to train dominant pairs of predators to avoid predation while maintaining their territories and keeping transient predators out of the area. The system has now gone into production in South Africa and is being distributed by its inventor.

Applying UAV Systems in Wildlife Management

Use of UAVs (unmanned aerial vehicles) in wildlife applications has been increasing in recent years as system costs have come down and regulations regarding their use have become more well-defined. Medium and larger UAVs can accommodate sophisticated payloads, allowing for missions using LIDAR to obtain measurements of vegetation height and fine-scale elevation data; high resolution video and thermal imaging for surveying wildlife; remote spraying for control of exotic plants; and broadcasting audio calls for hazing wildlife at oil spills. We have been developing some additional capabilities for potential use in wildlife research. The first is using UAV platforms as a means to remotely deliver anesthetic darts into larger wildlife species. This capability would allow for anesthetizing free-ranging deer, elk, bison, moose, etc. without the restriction of being close enough to use traditional rifle-based darting. Other drugs that could be delivered include those for immunocontraception and disease inoculation. We are also developing a drone-based remote net launcher system to allow for capture of both birds and mammals. Use of UAVs to aid in wildlife management activities that previously required more expensive aerial assets (e.g., airplanes or helicopters) or were not possible due to other restrictions, may allow managers to be more efficient and expand capabilities beyond what are currently available.

Pilot Studies Keep Me Flying High

Those who have been in the field of wildlife damage management very long probably have a file drawer full of half-baked ideas and ill-fated research projects that never should have seen the light of day. This paper will be a tongue-in-cheek look at the scientific method and saving grace of pilot studies. A pilot study is a small-scale test of the procedures to be used in a large-scale study. The goal of pilot work is not supposed to be the testing of hypotheses, but sometimes researchers just can’t help themselves. Beware of small sample sizes and the potential for false negative and false positive results. I have been involved in more pilot studies than I care to admit that ended up being a total bust, but there have been some that led to well-informed modifications of study designs and results that were immediately publishable because the variation in resultant data was low and results were clear cut. Pilot studies have expanded my knowledge of systems, study design, methodology, and the behavior of individual animals. I encourage the use of pilot studies in research associated with vertebrate pest management.

Sustained Release Long-life Lures and Bait Consumption Motivators for Rats

All current vertebrate pest control and detection devices require a lure to be effective. Even advanced multi-kill and multi-species technologies that can work remotely for extended periods without maintenance require lures to be effective. We have developed, over the past five years, several sustained release, long-life lures for controlling and monitoring rats. The lures contain blends of chemical compounds that we identified as attractive to rats. Our early prototype lures were effective at kill-trapping wild, free-ranging ship rats without the need for replenishment for six months. We have since engineered other lures to suit different applications (e.g., kill-trapping and monitoring) and users (e.g., pest control and conservation) and are also testing our lures as bait consumption motivators. We are currently transforming our prototypes into products for international markets.

Captive Canada Geese Acceptability and Toxicity Trials with Two Formulations of 0.005% Diphacinone Rodenticide Baits

The 0.005% diphacinone rodenticide pellets used in this study have been proposed for use in field applications to control introduced rodents on conservation lands in the state of Hawaii. Introduced rodents (especially Rattus spp.) cause a wide array of conservation problems in the Hawaiian Islands and on other islands. We assessed the acceptability and toxicity (should the pellets be consumed) of two rodenticide baits to Canada geese, a surrogate species for the endangered Hawaiian goose. Based on these trials with captive, wild Canada geese, it appears that neither the whole nor the chopped (to simulate broken or weathered baits) pellets pose a significant risk to the Hawaiian goose, a species considerably smaller than the Canada goose. The pellets (whole or chopped) were not accepted by the Canada geese during this study despite their having only a small amount of green grass sod as an alternative food. There were no mortalities of geese during the feeding trials and all geese remained healthy, based on body weights and packed blood cell volumes. The endangered status of the Hawaiian goose precluded using it as the target study species.

Evaluating the Efficacy of Carbachol at Reducing Corvid Predation on Artificial Nests (Abstract)

Nest predation often limits recovery of threatened and endangered birds, especially ground-nesting species. Accordingly, a variety of techniques are used to reduce the impact of nest predation on listed species. We examined the efficacy of conditioned taste aversion, a nonlethal technique designed to induce avoidance behavior in predators after being exposed to prey items that have been treated, usually with a chemical emetic that causes predators to become ill within minutes of consumption. We used carbachol (carbamyl choline chloride) as a taste-aversive agent to condition corvids responsible for high levels of nest predation on two federally listed species [the western snowy plover (Charadrius nivosus nivosus) and California least tern (Sternula antillarum browni)] breeding at Marine Corps Base Camp Pendleton, California. Carbachol is tasteless, colorless, and odorless, which makes it a preferred aversive agent as predators are unable to detect the chemical and therefore associate their resultant sickness with consumption of the prey item. We conducted two separate experiments in 2013 and 2014, during which we deployed 772 artificial nests during the first experiment and 760 artificial nests during the second experiment. Both experiments were conducted prior to the onset of egg laying for plovers and terns (i.e., Feb-Mar) and each artificial nest contained three quail (Coturnix sp.) eggs. During the first stage of both experiments all of the nests only contained untreated quail eggs, and nest predation was high with >90% of nests failing within 1-2 days of deployment. In subsequent stages, we deployed carbachol-treated eggs in increasing proportion. We used nest survival models to evaluate daily survival rates (DSR) of artificial nests in all stages of both experiments. During both experiments, DSR increased concomitant with a greater proportion of carbachol-treated eggs. Common ravens (Corvus corax) accounted for 98.1% (n = 471) of all artificial nest predations in Experiment 1, and 95.6% (n = 498) of all artificial nest predations in Experiment 2. Using carbachol as a taste-aversive agent was effective at reducing predation on artificial nests as illustrated by increased DSR (0.47 to 0.98 in the first experiment and 0.00 to 0.99 in the second experiment); however, transferability of this technique to plover and tern nests was not fully realized.

Control of Invasive Ship Rats, Rattus rattus, on Goat Island, New Zealand (Abstract)

Invasive ship rats (Rattus rattus) are the major threat to the native species and ecosystem of Goat Island (9.3 ha), New Zealand. The island is only 100 m away from the mainland, which imposes a risk of incursions by rats swimming over. Accessibility depends on weather and tide times which makes regular trap servicing complicated. In 2016 we extended an existing trapping grid of 8 kill traps (DOC200; Department of Conservation, New Zealand) with 10 self-resetting traps (Goodnature A24s; Goodnature Limited, Wellington, New Zealand) to improve current management and ideally achieve eradication. Before our study started, DOC200s on the island had not been serviced for six months. Rats were active even during the day and rat numbers were assumed to be high. The DOC200 kill traps were lured with an egg and A24s were lured with Goodnature automatic lure pumps (ALP) baited with chocolate formula for rats. The A24s were equipped with Goodnature digital strike counters to document the number of rats killed by the self-resetting traps. All devices were on average checked every 49 days from August 2016 to October 2017. DOC200s were reset after triggering or after three months, whichever occurred first. ALPs were replaced in January and July 2017. Gas cartridges of the A24s were replaced when the strike counter showed 20 or more. A substantial number of rats were killed on the island (242 by A24s and 27 by DOC200s) in 8,838 uncorrected trap nights between August 2016 to October 2017 (Table 1). The initial number of individuals killed by A24s in the first month after deployment in August 2016 was high. The number of rats removed by A24s remained at a high level from November 2016 until June 2017. The number of A24 kills varied widely between the beginnings of the breeding seasons across the two years, with 46 individuals killed between September and November 2016 but only 4 kills between August and October 2017. Even though initial trapping success was high, eradication could not be achieved and the self-resetting traps did not perform better than traditional kill traps once rat abundance was low. The Goodnature A24 has shown the potential to work effectively for initial knock-down when rat numbers and activity were high. The advantage over traditional single kill traps, like the DOC200, was the low need for servicing. However, once the population density was reduced to a lower level, this advantage vanished. Most kills by A24s happened during the breeding season in 2016 in the first third of the study. In the last three months of the project the kill numbers did not differ meaningfully from the DOC200 kill numbers. Even though trapping numbers were low, rat abundance was still assumed to be high. After our study had finished rat control on the island using these devices was continued by local community volunteers. A further 357 rats were caught between June 2018 and March 2020, indicating no decline in rat captures. On 1 September 2019 and 1 March 2020 tracking tunnel indices were 100% (K. Tricklebank pers. commun.). In March 2020 initial cost for a DOC200 was NZD$145.00. The purchase costs for a Goodnature A24 with lure and gas for 6 months was NZD$169.00 (excluding digital strike counter). For the first six months the differences in costs were moderate. However, after six months, the material costs for servicing a DOC200 was NZD$0.55 (one freerange egg), or less when using peanut butter. The servicing cost for a Goodnature A24 is NZD$19.00 (gas cartridge + ALP). On Goat Island, servicing costs for a six months period were approximately NZD$9.00 for eight DOC200s and NZD$190.00 for ten A24s. Higher costs for A24 purchase and servicing compared to DOC200 were not compensated by noteworthy higher kill numbers once rat numbers were reduced. However, A24s performed well during peak times and labour costs were not considered in our study. Self-resetting devices at one per hectare did moderately reduce rat numbers in an area where kill trap maintenance was time and cost intensive but suppressing to very low rat numbers or achieving eradication requires additional investment in the system (e.g., a combination of different tools including toxins or a higher density of devices).

Measuring Density and Activity of Feral Cats Using Camera Traps on San Clemente Island, CA

Feral cat (Felis catus) predation has negative impacts on native species, especially in island ecosystems (Vitousek 1988, Dowding and Murphy 2001, Bonnaud et al. 2011, Doherty et al. 2016). Feral cats are prolific opportunistic carnivores that prey upon whatever food source is most abundant and preferred (Parsons et al, 2019). They are the cause of extinctions of a plethora of species world-wide. Feral cats on San Clemente Island (SCI) are non-native predators to various endemic species that include the San Clemente Island deer mouse (Peromyscus maniculatus), Island night lizard (Xantusia riversiana), San Clemente Island Bell’s sparrow (Artemisiospiza belli clementeae), and the San Clemente Island loggerhead shrike (Lanius ludovicianus mearnsi) (Biteman et al 2015). Feral cats on SCI also compete for prey items with a subspecies of the Island fox (Urocyon littoralis clementae) that is naturalized to San Clemente. Understanding the feral cat’s activity patterns and estimating their density are important to improve the efficacy of feral cat management efforts. Camera traps are used to quantify activity patterns and population sizes of a variety of species world-wide, but have seldom been used to address these questions with feral cats, and no study has been done on SCI. We used camera traps on SCI to quantify activity patterns, identify high density areas, and determine feral cat population size. Our study took place from November 2018 to March 2019. We had 75 stations with two cameras at each (Figure 1). We checked each trap every two weeks to maintain bait, batteries, and SD cards. Cameras at a station were placed 5 m apart and were facing each other. Stations were always set on a game trail. We used two bait types (i.e. feline and general mammalian predator) at each station, with one piece of bait in front of each camera. Photos from SD cards were manually sorted; photos with no wildlife in them were deleted. Photos were uploaded to a camera trap photo processor called Timelapse2, which extracted date and time, and gave a unique identifier to each photo. We manually entered the species seen in each photo. We used N-mixture models to calculate density, activity, and population data for feral cats. We used program R to run these statistics. We found 114 individual cats identified on 75 cameras over the 4 months of testing. We estimated the population at 319 to 331 cats (95% CI). Activity peaks were found at 1:30 pm and 7:30 pm daily (Figure 2). Spatial density varied but most of the dense areas were located far from roads (or at least outside of shooting distance) and also in exclusion zones (Figure 1). We think multiple factors contributed to the daily patterns. Winter climate in southern California is rainy and rainy conditions likely forced cats into more daytime activity for better thermoregulation. We have been conducting nighttime control of feral cats on the island for 20+ years; nighttime hunting pressure may have shifted their activity toward a daytime peak. Both of the activity peaks we calculated are during hours, when we have not had full firearm access (e.g., limited to 40 yards and closer), and our usual method of identifying cats (by spotlighting) is ineffective. Spatial density is another factor: San Clemente is a valuable and heavily used training ground for the U.S. Navy, so there are areas on the island we cannot access at certain times, or ever. Due to firearms range, terrain, and access time, efforts have been focused along roads, but cat “hot spots” are far off the roads, in or around exclusion zones, or a combination of the two. All this results in large areas where predator control cannot be carried out. More efforts to hike and hunt are being made to extend our reach, giving better data and the ability to remove cats efficiently from high density areas where they have been unchecked. Efforts to hunt during the day should be considered. Other control efforts elsewhere have used air rifles (which do not qualify as firearms), that could be used during the day. We could also use sit-and-wait methods (i.e., use attractants to lure cats in; then remove the cats). We conclude that our efforts could be doubled by adding day hunting in high density areas off the road.

Island Eradications of the Future: RNAi as a Selective Tool

Rodents cause devastating damage to both agriculture and ecosystems worldwide. Invasive rodents are commonly found on islands, historically free of these animals, and have significant negative impacts on both native plant and animal species. Rodents are exceptionally well adapted to their environments and therefore, quite challenging to control. Current control strategies often include large scale applications of toxicants, which have potential adverse effects on non-target wildlife. In island ecosystems, these adverse effects are a major hurdle to eradication efforts. The time and financial resources required to minimizing risks to non-target species and performing post-eradication exposure monitoring can limit the number of islands from which rodents are successfully eradicated. Therefore, the development of new species-specific rodenticides would be a valuable advancement in the effort to control these pest species, especially for island eradications. To that end, USDA Wildlife Services is investigating the use of interfering RNA (RNAi) as a novel way to control rodent species. RNAi reduces the amount of a specific protein that is made by a cell. This is done through post-transcriptional gene-silencing. The RNAi pathway is initiated when a small section of double stranded RNA is introduced into the cytoplasm of a cell. This double stranded RNA comprises a guide strand and a passenger strand. In the first step of the RNAi pathway, the foreign RNA is incorporated into an enzyme complex called RNA-induced silencing complex (RISC) at which time the passenger strand is degraded. The RISC/RNA complex then finds the complementary mRNA made by the cell and binds to it. Subsequently, the RISC complex degrades the complementary mRNA. This breaking down of the mRNA prevents the synthesis of the corresponding protein. The reduction in protein synthesis is the benchmark of RNAi and is how it will be used to elucidate lethal physiological changes in pest species. The species specificity of RNAi depends on the selection of portions of genes that are unique to the target animal species. By screening the rodent genome and comparing sequences of rodent genes to non-target species, we can choose sections of genes that are present in the pest species and absent in the non-target species. Previous research has established guidelines for both the nucleic acid composition of RNAi sequences and their location in the corresponding mRNA that facilitate maximum inhibition of protein synthesis while maintaining species specificity. Therefore, unlike current rodenticides, if non-target species consume the RNAi they will not be affected. This specificity could allow for the eradication of rodents from islands that have historically not been feasible. For RNAi to be useful as a rodenticide, it will likely have to be formulated in a bait for oral consumption. This is a significant hurdle: most RNAi based therapeutics for human use are formulated for intravenous or subcutaneous injection. Like all rodenticide baits, an RNAi-based bait will have to be stable in a wide range of environmental conditions and have a long shelf life. However, once consumed by the target animal, RNAi-based baits will have to be significantly more complex than traditional toxicant baits. The double stranded segments of RNA will have to be protected from the changing pH of the digestive tract and absorbed into the systemic circulation while maintaining viability. Once in circulation, RNAi molecules must be delivered to the target tissues at concentrations high enough to elucidate a physiological response. Advances in bioengineering have given researchers products that both hide RNAi inside stable exterior shells and direct these carrier molecules to the site of action. These cutting-edge technologies make the development of a RNAi-based rodent bait a feasible option. The use of RNAi for rodent control shows promise because of its species specificity and low non-target impact. RNAi sequences are selected to sections of the rodent genome that are significantly different from non-target species genes and therefore do not bind to and degrade the non-target mRNA. Formulating RNAi into oral baits presents challenges but recent advances in bioengineering have led to the development of mechanisms for delivery useful for this application of RNAi. RNAi-based baits will be a great benefit to efforts to eradicate rodents off islands because they will reduce the time and funding necessary to mitigate risks to non-target species and the environment.