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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.


The future of wildlife damage management--and why I want to be a part of it

I am very pleased to be involved with wildlife damage management. Explaining why is what I hope to accomplish during this opening address for the 17th Vertebrate Pest Conference. The premise behind my remarks this morning is really quite simple. No matter what we choose to call it, working with vertebrate pests in a nuisance, damage, or human health or safety context is a "growth industry." We have opportunities and challenges not available to some segments of the wildlife management profession. As an Extension Wildlife Specialist, I have had the opportunity to interact with the public at many different levels over the past 18 years. That experience, plus more recent work with the Wildlife Society's Wildlife Damage Management Working Group (WDMWG), The National Animal Damage Control Association (NADCA), and the various wildlife damage conferences including the VPC, has allowed me to develop a list of opportunities and challenges for your consideration.

Introducing the National Wildlife Research Center

The paper summarizes the background and historical events leading to the creation of the National Wildlife Research Center (NWRC) and describes the status of its research program and facilities development in Fort Collins, Colorado. Also, the relationship of the NWRC to the Denver Wildlife Research Center is presented.

The status of nuisance wildlife damage control in the states

State fish and wildlife agencies and nuisance wildlife control operators must work together whether or not they actively choose to. In this paper, their relationship is likened to a marriage between two (not so likely) partners. In an attempt to assess the status of this relationship the International Association of Fish and Wildlife Agencies, The Wildlife Society's Wildlife Damage Management Working Group, and the National Animal Damage Control Association developed a survey that addressed the level of state agencies' oversight of nuisance wildlife control operators (NWCOs). Responses were received from 47 states, 1 territory, and 17 ADC state offices. This report concentrates on the responses from the U.S. states and territories. Currently 77% of states perform nuisance wildlife control activities. Private agents may euthanize nuisance animals for property owners in 95% of the states, and are allowed to relocate nuisance wildlife in 91% of the states. Most states do not require NWCO's to carry general liability insurance. Some states do not have a well-defined method for monitoring compliance with laws and regulations dealing with nuisance wildlife control activities. There appears to be a great deal of gray area in the relationship between NWCOs and the state agencies. National guidelines for the nuisance wildlife control industry may help clarify the responsibilities of the states and NWCOs with respect to each other and the private landowner.

Analysis of vertebrate pest research

Research on vertebrate pest control is mostly empirical, focusing on control of species X in location Y using method Z. Such an approach is needed. The science of vertebrate pest research is developing some generalizations across species, locations, and methods. This paper further explores such generalizations by discussing six questions asked by Hone (1994), the answers to which are relevant to vertebrate pest research world-wide. Several case studies are examined, with emphasis on control of damage by small mammals and predation control. Suggestions are made for future research.

Towards "best practice" vertebrate pest management in Australia using virally-vectored immunocontraception

Australia has 26 species of introduced pest mammals that cause extensive damage to agriculture and the conservation of native wildlife. Past efforts tried to eradicate them. This focus on reducing pest numbers rather than the outcome, reduced damage, has had limited success. Under its Vertebrate Pest Program, the Bureau of Resource Sciences has developed principles and a strategic approach to managing pest damage. Close cooperation with land managers as co-researchers and co-learners is an essential element, as is a coordinated group approach to pest management. The approaches is illustrated with an example.

Ecological challenges to controlling wild rabbits in Australia using virally-vectored immunocontraception

The European wild rabbit in Australia threatens the sustainability of agriculture and conservation of native flora and fauna. Improved means of reducing these impacts are sought including effort to develop virally vectored immunocontraception (VVIC). VVIC for the wild rabbit involves complex interactions between the rabbit, myxoma virus and insect vectors of the virus. Development of the method includes not only reproductive molecular biology and genetics and manipulation of virus genetics, but also many problems in reproductive biology, ecology and population dynamics of the rabbit in diverse environments. Furthermore, epidemiology of enzootic myxomatosis, and behavior and population dynamics of several vector species of mosquito and flea must be considered. Some of these ecological problems are described with a brief description of the approach to experimental analysis.

Education and training integral part to 1080 possum control in New Zealand

New Zealand currently has large scale possum and rabbit operations being carried out on about 103 of its land area. Education and training are integral to possum control in New Zealand because of the heavy reliance that the control agencies in New Zealand place on toxic baiting with 1080 (sodium monofluoroacetate). Education of the general public is treated as a high priority since without their approval many of the operations would not be carried out. It is equally important that school children are advised on what toxic baits look like and why pest control operations are required. Training of pest control staff is also considered important as it is vital that all staff are well trained in the latest technology and at the same time can answer inquiries with the latest results of research.

Mole control - a historical perspective

Various methods and approaches, including chemical and physical repellents, flooding, burrow fumigants, poison baits, vibrating devices and exclusion, have been explored for reducing mole problems. In addition to these, habitat management through reducing the moles food supply has received considerable attention, but environmental concerns and the lack of consistent results have tempered this approach. Over the years, trapping remains the best and most useful method of mole control. The pros and cons of some of the methods are discussed, along with some historical perspectives. The emphasis is placed on the Broad-footed mole, Scapanus latimanus, of California.

Dealing with wild pig depredation in California: The strategic plan

This report provides an historical background of the presence and management of wild pigs in California, including their introduction and range expansion, classification as game animals in 1957, and current presence within counties in the state. History of depredation permits issued by the California Department of Fish & Game is provided, as well as number of animals taken under permit and the types of damage incurred by permit applicants. A strategic plan for wild pig management, as required by state legislation, for the period 1995-2000 is described and discussed.

Federal and state fish and wildlife regulations and other pertinent California laws

Working knowledge of Federal and State Fish and Wildlife regulations and other laws are critical for today's commercial applicator in the vertebrate pest control business. The ever-changing focus on environmental protection, endangered species considerations, occupational health and safety, and animal rights have put vertebrate pest control operators in the precarious position of correctly interpreting the steady stream of laws and regulations passed by government. The consequences of failing to stay abreast of these changing regulations and correctly interpreting them can lead to very costly fines and possible imprisonment. Maintaining close contact with the many agencies that regulate the pest control industry and their enforcement personnel is essential to navigating and promoting a successful, long-term business in today's hostile, anti-business environment.

Developing wildlife management into a successful business

Wildlife management has been developed into a successful business. The company was set up after the principal shareholder was made redundant after over 30 years in the wildlife management field. The company has been successful, as it diversified into a consultancy and supply company, and targeted a wide range of animal species and equipment.

An overview of animal damage control (ADC) assistance to the vertebrate pest management industry

The Animal Damage Control (ADC) program has had a long history dating back to 1885. ADC was officially established in 1931 under the United States Department of Agriculture. In 1939, the program was moved to the United States Department of Interior's Fish and Wildlife Service. In 1996, ADC was transferred back to the USDA and placed under the Animal and Plant Health Inspection Service. The mission of the Animal Damage Control program is to provide federal leadership in managing problems caused by wildlife. Current program assistance includes: a) technical assistance in wildlife management; b) conducting research and development activities related to wildlife damage control; c) providing a source for a variety of animal damage control tools; d) development and transfer of scientific and technical information on wildlife damage issues; e) helping obtain migratory bird depredation permits; f) providing training sessions on wildlife damage management issues; and g) registering and maintaining chemical products for wildlife management.

The persistence and secondary poisoning risks of sodium monofluoroacetate (1080), brodifacoum, and cholecalciferol in possums

To determine the risk of secondary poisoning for animals preying on sub-lethally poisoned brushtail possums, captive possums were treated with near-lethal doses of sodium monofluoroacetate (1080) or brodifacoum, and toxicant concentrations in blood and tissue were monitored over time. Sodium monofluoroacetate was rapidly eliminated from the blood (within three days). Brodifacoum was retained in the liver and, to a lesser extent, the muscle of possums for eight months after dosing. To determine the potential risk for animals scavenging on the carcasses of possums poisoned with cholecalciferol, cats were fed poisoned carcasses for six days. No changes in behavior, appetite, or body weight were observed. Serum calcium concentrations increased slightly, but remained within the normal range for cats.

Rodents and cover crops - a review

Inter-row plantings of herbaceous cover crops has become a widely accepted practice by orchard and vineyard managers. Cover crops, used as part of a production management system, are not considered a cash crop and are therefore selected by individual growers for various reasons. Little is written regarding the relationship of cover crop management and the impact on rodent populations. This paper reviews the recent literature and examines how cover crop species and cultivar selection along with management procedures may be influential in limiting rodent populations and their damage to cropping systems.

The Texas oral rabies vaccination project and the experimental use of Raboral V-RG rabies vaccine in the south Texas coyote rabies epizootic

Beginning in October 1988, Texas experienced an expanding epizootic of canine rabies, in South Texas, which now involves 21 counties where a total of 678 confirmed cases (50% in coyotes, the majority of the rest in domestic dogs, with 76 "spill-over" cases found in 7 other species). Some 2,000 persons have received post-exposure rabies treatment, and there have been 2 human fatalities. The Texas Department of Health has led the initiation of an experimental program to use an oral rabies vaccine, Raboral V-RG, over the next 4-5 years with the goal of pushing the epizootic southward and eliminating it from Texas. Success in reducing rabies during 1995, when 830,000 baits were distributed over 15,000 acres, is described. Data on bait uptake and immune status of coyotes are presented.

Zoonotic diseases of carnivores and occupational safety issues for predator control employees

The paper highlights some important zoonotic infections of carnivores in North America, including bacterial, viral, and parasitic infections, particularly those of interest to wildlife biologists and managers. The etiologic agents, routes of transmission, reservoirs, and methods for prevention are emphasized. Occupational safety issues for people working in predator control are discussed.

Investigations and management of epizootic plague at Ice House Reservoir, Eldorado National Forest, California, 1994 and 1995

The occurrence of plague (Yersinia pestis) at Ice House Reservoir in 1994 and 1995 was characteristic of widespread epizootics in high use recreational areas of California. Staff of the Vector-Borne Disease Section investigated these epizootics and found dense populations of plague susceptible California ground squirrels (Spermophilus beecheyi) with high numbers of fleas, primarily Diamanus montanus, the most important plague vector. This combination indicated a high risk of plague exposure to campground users. A non-fatal human case of plague, contracted at Mountain Camp 11, was reported after the initial epizootic investigation. The patient's exposure occurred prior to the reporting of the epizootic die-off among the California ground squirrels. The plague investigation included direct observations, animal trapping, and laboratory testing of rodent carcasses, sera, and fleas. Plague management and prevention included flea control with 2% Diazinon dust and rodent population reduction using 1% zinc phosphide treated grain. Evaluation of the 1994 applications indicated a successful reduction of rodents and fleas. However, the need for an ongoing management program was emphasized in 1995 when the plague epizootic continued. Intrusion of plague infected rodents and their fleas necessitated a 1995 treatment in the four campgrounds involved.

Population densities and disease surveys of wild pigs in the coast ranges of central and northern California

In 1994 and 1995, 233 different wild pigs were captured during population research at seven research sites focused primarily in the coastal regions of central and northern California. Mark-resight data and information on wild pig movements were used to assess wild pig population densities at those sites. Population densities ranged from 1.01 wild pigs/km2 in Mendocino County in 1994 to 3.32 wild pigs/km2 in Santa Clara County in 1995. Comparisons of population densities between years at three research sites suggested that wild pig populations increased in 1995 in response to favorable forage conditions after the wet fall and winter of 1994-95. Serum samples collected from 462 wild pigs at 28 different sites were screened for exposure to brucellosis and pseudorabies. Preliminary results were that seropositive results for brucellosis were noted at only three sites, whereas no animals were confirmed seropositive for pseudorabies. Although analyses of these two diseases are continuing, test results for trichinellosis, toxoplasmosis, and sylvatic plague reinforce previous warnings to hunters and consumers that sanitary handling and cooking of wild swine meat are warranted.

Preliminary study of the genetics of resistance in the house mouse

A wild house mouse (Mus domesticus) population originally trapped near Reading, Berkshire, United Kingdom, and maintained as a colony in the laboratory, was subjected to the discriminating feeding period of the warfarin resistance test, as used by Wallace and MacSwiney (1976) and derived from the work of Rowe and Redfern (1964). Eighty percent of this heterogeneous population survived the resistance test. A similar proportion of the population was found to survive the normally lethal dose of bromadiolone administered by oral gavage. The majority of this population of mice were classified as "warfarin-resistant" and "bromadiolone-resistant." The dose of of bromadiolone administered by oral gavage appeared to give good discrimination between susceptible and resistant individuals. The results of breeding tests indicate a single dominant gene that confers both "warfarin-resistance" and "bromadiolone-resistance," with complete expression of the resistance genotype in both males and females. Individual mice were classified as to genotype by back-crossing to a homozygous-susceptible strain, and resistance-testing the F1 generation. Separate strains of homozygous-resistant and homozygous-susceptible house mice are now being established.

A profile of depredating mountain lions

Information regarding the demographics and physical condition of mountain lions (Felis concolor) killed during damage control efforts in Nevada was gathered and compared to sport harvested mountain lions. The average age of depredating male lions was 4.92 years of age compared to 4.95 years for sport harvested males. Depredating female lions were older than sport harvested females averaging 5.09 years compared to 4.44 years. Older age class mountain lions of both sexes were more likely to commit depredations than expected. Male lions were involved in depredations 45% more often than females. Domestic sheep comprise more than 90% of depredation events in Nevada.

Leg injuries to coyotes captured in standard and modified Soft Catch traps

Leg injuries of coyotes (Canis latrans) captured in standard No. 3 Soft Catch traps were compared with those captured in the same trap type modified with two additional coil springs. One hundred thirteen coyotes were trapped in southern California in conjunction with livestock predator control operations, 53 in standard traps, and 60 in modified traps. Observed injuries were similar in both trap types. The most frequent injuries were edematous hemorrhages and small cutaneous lacerations. Injuries, such as joint luxations and bone fractures, were noted more frequently for coyotes trapped in standard Soft Catch traps.

Agelaius blackbirds and rice in Uruguay and the southeastern United States

Throughout the world, wherever rice is grown, birds that damage the crop are attracted. The situations are particularly interesting in Uruguay and the southeastern United States where different species of blackbird have adapted to rice cultivation. In the two countries, rice production practices differ in several respects such as seeding rate, seedbed preparation, and insect control practices. Furthermore, although they are congeneric, the major rice pest species differ in important ways. For example, in Uruguay, Agelaius ruficapillus usually nests in the rice field, whereas A. phoeniceus, in the U.S., does so only rarely. Agronomic and ornithological aspects of these two blackbird-rice systems are discussed and implications for development of effective damage management strategies are evaluated.

Disaccharide intolerance of European starlings

The use of disaccharides to discourage bird depredation to agricultural crops has elicited some interest during the last few years. Data developed in these trials indicate that several avian species are intolerant to sucrose because of the lack of sucrase enzymes in their digestive systems. Based on this research it is hypothesized that progressively increasing rates and volumes of solutions would elicit consistent adverse stress reactions. Furthermore, that if birds were intolerant to sucrose, because of their co-evolutionary development with plants, then they should Jack the ability to digest lactose. The data developed in these trials does not support either hypothesis. A maximum of 603 of the birds tested showed stress symptoms to 0.75 M sucrose (6.26 mg/Kg body wt.) and 1.00 M lactose solutions (9.15 mg/Kg body wt.) when the birds were subjected to 2 cc treatments. Less than 40% were stressed by the lower concentrations. No adverse reactions were noted with 1 cc concentrations of either solutions or rates. Treating fruit with sucrose did not appear to affect the results until 1.00 M (3.83 mg/Kg) sucrose solutions were applied. No adverse results were obtained with lactose treated fruit.

Use of the modified Australian crow trap for the control of depredating birds in Sonoma County

The Modified Australian Crow (MAC) trap to control depredating birds can be a very humane, target species specific and effective bird control tool. Pertinent topics will include legal status, timing, and care of trapped birds. The following are also discussed: species identification, trap construction, and placement and humane euthanasia methods.

Overhead wires reduce roof-nesting by ring-billed gulls and herring gulls

The authors evaluated the effectiveness of overhead wires in reducing roof-nesting by ring-billed gulls (Larus delawarensis) and herring gulls (L. argentatus) at a 7.2 ha food warehouse in Bedford Heights, Ohio during 1994-1995. In 1994, stainless steel wires (0.8 mm diameter) were attached generally in spoke-like configurations between 2.4 m upright metal poles spaced at 33.7 m intervals over the main portion of roof. The 6 to 14 wires radiating from each pole created a mean maximum spacing between wires of about 16 m. Nesting by ring-billed and herring gulls was reduced by 76% and 100% in 1994 and by 99% and 100% in 1995, respectively, compared to 1993 pretreatment levels (1,011 ring-billed gull nests and 98 herring gull nests). Ring-billed gulls that constructed nests after wire installation gained access to the roof where wires were not installed along the roof edge, where wires were broken, by hovering over wires and landing between them, or from structures such as air conditioners that were at or above the level of surrounding wires. Initial placement of overhead wires above roof structures and regular maintenance of broken wires is recommended to increase effectiveness. Mean maximum spacing of 16 m between wires was effective in excluding nesting by herring gulls; however, narrower spacing is necessary to exclude nesting by ring-billed gulls. Also, many of the ring-billed gulls displaced by wires from the warehouse in 1994 relocated to nest on an adjacent building without overhead wires. Thus, although overhead wires can be effective in reducing nesting by gulls on roofs and in other urban situations, management should be considered at a scale broader than specific problem sites as displacement of nesting gulls may cause relocation of the colonies to surrounding areas.

Nest material as a delivery method for avicides: Preliminary tests with African weaver finches

To evaluate the potential of using nesting material as a medium for avicide delivery, five organophosphates (Dasanit®, Volaton®, fenthion, parathion, and Cyanophos®) were tested on small groups of paired male-female quelea (n = 4 to 9). Toxicants were presented to each pair of birds on five 13-cm strands of cotton string after a preliminary screening for male nest weaving behavior. Tested concentrations ranged from 100% technical grade to 0.003% compound diluted with acetone. Dasanit® was found to be the most effective candidate with some lethal effects noted at 0.012%. An optimal concentration for Dasanit® was estimated to be 0.80% based on combined male and female mortality (72%). This level was further evaluated in two aviary cage tests using 25 male-female quelea pairs during three-day exposure periods. A first replication yielded mortality ratios of 23:25 (92%) for males, but mortality ratios of only 1:24 (4%) for females. The second replication yielded mortality ratios of 24:25 (96%) for males and 11:25 (44%) for females. Females in the second group showed more weaving attempts than those in the first replication group, which could explain the pronounced mortality difference. Safety concerns about the use of toxicant-laden nesting material have not yet been evaluated in Africa. These concerns need to be addressed relative to the knowledge and literacy level of the local people applying the materials and to their awareness of methods of limiting pesticide exposures to the general public.

Effects of stage of nut development and simulated rat damage on macadamia yields

Black rats (Rattus rattus) cause extensive damage in Hawaiian macadamia (Macadamia integrifolia) orchards. In a previous study, extensive and persistent snap trapping significantly reduced rat populations and depredations on developing macadamia nuts, but had little effect on subsequent yields of mature nuts. This suggested that macadamia trees may compensate for rat damage, and that commonly used indices based on rodent activity and proportion of nuts damaged may overestimate the impact of rodent depredations and exaggerate the effectiveness of control measures. To clarify the effects of rat feeding on developing macadamia nuts, two levels of damage at two times during nut development and evaluated yields of mature nuts were simulated. Both number of nuts per raceme (P = 0.0001) and total weight of mature kernels per raceme (P = 0.0001), but not mean weight per mature kernel (P = 0.90), varied among treatments. Both number of nuts and total weight of kernels decreased (P < 0.05) with increasing damage. Time during nut development that damage was simulated had no apparent effect (P > 0.05) on yields. These results indicate that racemes did not compensate for damage by retaining other nuts on the same raceme that might otherwise have dropped prematurely. A variance component analysis was also conducted to determine how best to sample the orchard in a practical fashion while minimizing potential sources of bias and retaining sensitivity for distinguishing among treatment effects. All of the random variability in the number of nuts per raceme and total weight of nuts per raceme, and > 93% of the variability in mean weight per mature nut were due to variability between racemes on a tree. Thus, blocking was not needed to control for variability among the different areas in the orchard; sampling fewer trees and concentrating available resources on measuring more racemes per tree would have provided a more sensitive comparison of treatments. Focusing on entire branches or trees instead of racemes as experimental units might have provided a more realistic model for investigating compensatory mechanisms in macadamia trees.

Economic effectiveness, efficiency, and selectivity of fox squirrel trapping in pecan groves

Trapping is the most common damage management practice employed by pecan growers suffering fox squirrel (Sciurus niger) depredation. The author evaluated the economic effectiveness of foot-hold trapping fox squirrels in native pecan groves from 1988 to 1991. Trapping significantly reduced squirrel damage the first and second year of treatment in all three study areas relative to the initial untreated year. This reduction was valued at $38.63 to $279.51/ha. In 1990 the author tested the relative efficiency and selectivity of five trap types. Number 110 body traps performed with the best combination of efficiency, selectivity, and cost of the trap types tested.

Field efficacy of diphacinone grain baits used to control the California ground squirrel

Diphacinone treated oat groats were effective in reducing populations of California ground squirrels (Spermophilus beecheyi) by more than 84%. Two concentrations of active ingredient (0.005% and 0.01%) were compared, as well as two application methods: spot baiting and bait stations. Squirrel activity on test plots was assessed before and after bait applications using visual counts and active burrow counts. There was good correspondence between results of the two activity indices. There was no significant improvement in efficacy provided by the higher concentration of diphacinone. Bait consumption was much lower on bait station plots. Squirrel carcasses were found on treated areas at a rate of approximately one carcass per acre. Tissue residue analysis determined that residue loads were nearly identical regardless of the concentration of bait consumed or method of baiting.

Palatability of rodenticide baits in relation to their effectiveness against farm populations of the Norway rat

The palatability of 12 rodenticide baits, formulated to vary from poorly accepted to well accepted, was measured in laboratory choice tests against Wistar and wild-caught Norway rats. The baits, derived from six bait bases and two active ingredients, difenacoum and bromadiolone, were simultaneously tested in the field against 24 farm infestations (2/formulation) in order to investigate the relationship between palatability and efficacy. Bait acceptance in laboratory tests, with EPA meal as the challenge diet, varied from 7.0 to 50.6% for Wistar rats and 3.7 to 85.1% for wild rats. Changing the challenge diet to a ground-up laboratory animal food significantly increased the apparent palatability of three selected baits to Wistar rats, although the relative palatabilities between the formulations remained the same. Bait acceptance, as measured in the laboratory, was unrelated to the degree of control achieved in farm treatments. The presence or absence of alternative food and whether the baits were placed in containers or applied directly into rat burrows appeared more likely to determine the outcome and overwhelmed any influence due to bait palatability. The combined effect of container- and burrow-baiting reduced the rat populations by an average 96.8% with 16 of the 24 populations tested completely eradicated. The least palatable baits dispensed into burrow entrances controlled rats on all farms, including those with abundant food sources.

Zinc phosphide residues in voles: Scenarios showing low risks to domestic cats and dogs

Zinc phosphide (Zn3P2, CAS #1314-84-7) is an acute rodenticide having numerous agricultural applications. This paper estimates the risk of mortality posed to domestic cats (Felis domesticus) and dogs (Canis familiaris) from ingestion of voles (Microtus spp.) that succumb to 2.0% Zn3P2 baits. Following a brief review of direct/indirect studies and incident reports relevant to nontarget-Zn3P2 effects and vole control, four scenarios of vole-carcass ingestions needed for light and heavy cat and dog predators/scavengers to receive approximate lethal doses (ALDs = 40 mg/kg) of undigested rodenticide are described. Scenarios were derived using values reported by Sterner and Mauldin (1995) as the maximum 8.2 mg Zn3P2 ingested (ad libitum) and average 1.7 mg Zn3P2 whole-carcass residue. Extrapolating these "worst-case" loads to 2 and 6 kg cats and 1 and 36 kg dogs showed that between 5 and 847 Zn3P2-baited vole carcasses must be consumed in fairly rapid succession for these nontargets to ingest cumulative ALDs. The likelihood that even light (≤ 1-2 kg) cats and dogs will find and rapidly (≤ 24 h) ingest multiple (≥ 5) Zn3P2-dosed vole carcasses under registered applications seems remote.

Mongolian rangelands: Rodent problems and approaches to alleviate damage

Rodents are a major constraint to forage production for livestock in Mongolia. A technical program to identify the magnitude of the problem and strengthen the research capabilities of Mongolian rodent specialists was initiated in 1994. The Brandt's vole is the most widespread and the most detrimental rodent to the steppes of Mongolia. Limited resources inhibit activities by the Mongolian Plant Protection Service to reduce rodent populations. Alternative means to monitor vole activity were developed. Laboratory and field trials showed that voles were susceptible to zinc phosphide treatment and indicated how bait acceptance could be improved.

Impacts of field-dwelling rodents on emerging field corn

The Conservation Reserve Program (CRP) has produced nearly 600,000 ha of exceptional wildlife habitat in Nebraska. Unfortunately, several species of rodents that inhabit CRP grass fields cause damage to agricultural crops. The emergence of corn seedlings in a 4-row strip of no-till field corn, planted in a 64 ha bromegrass field in northeastern Nebraska was examined. The most common rodent species in the study area was the deer mouse (Peromyscus maniculatus), of which 18 were captured within 10 m of the planted strip during one evening (400 trap nights). Corn seedling emergence in unprotected control areas [mean = 19.2 plants/dekameter of row (dor)] appeared to be lower than in areas protected with welded wire exclosures (mean = 23.7 plants/dor). An in-furrow application of 2% zinc phosphide pellets (2.75 kg/ha) also contributed to an increase in emergence (mean = 21.9 plants/dor). Differences among the treatments, however, were not significant (P = 0.76). Additional research is needed to develop methods to reduce wildlife damage in crop fields that incorporate conservation tillage practices or are adjacent to or converted from CRP fields.

The pocket gopher as a pest in Mexico

Pocket gophers of the genus Orthogeomys and Pappogeomys are major pests in rangeland and agricultural areas throughout Mexico. Control relies on the indiscriminate use of fumigants and poison baits. These controls are applied in a haphazard manner; do not provide long-term benefits and the non-target hazards and public safety risks are perceived to be extremely high. Studies indicate that as a result of reinvasion of treated areas or territory expansion of animals surviving the control procedure, controls relying on removal of animals may be limited unless applied at frequent (every three months or less) intervals.

Perceptions of wildlife damage by conservation reserve program contract holders in Riley County, Kansas

Twenty-five Conservation Reserve Program (CRP) contract holders in Riley County, Kansas were surveyed by telephone to assess their perceptions of wildlife damage relative to CRP plantings. Sixty-four percent experienced wildlife damage on their farm or ranch. Respondents felt that five species causing damage on their farm or ranch had become more common due to enrollment of lands in the CRP. White-tailed deer (Odocoileus virginianus) accounted for 64.3% of these observations, followed by wild turkey (Meleagris gallopavo), eastern cottontail (Sylvilagus floridanus), striped skunk (Mephitis mephitis), and Virginia opossum (Didelphis virginiana), which accounted for 14.3%, 7.1%, 7.1 %, and 7.1% of the damage observations, respectively. Only 12.5% of respondents attempted to control wildlife damage, and none felt that wildlife damage was severe enough to preclude future enrollment in programs such as the CRP. Most respondents allowed hunting or trapping by non-family members on their CRP lands (68.8%), but none felt that increased hunting or trapping would reduce the amount of wildlife damage they experienced. All respondents felt that the benefits of the CRP exceeded costs associated with wildlife damage and that the program was highly beneficial overall.

The Washington ADCP-a private collaboratice effort to address biological, economical, and social constraints to reduce wildlife damage

The Washington Animal Damage Control Program (WADCP) operates within the general structure of the Washington Forest Protection Association. The general goal of the WADCP is to resolve wildlife damage issues in an economically feasible and socially acceptable manner. The four components of the WADCP are program management and administration; support of individual member activities; research, monitoring, and surveys; and promotional and educational activities. An overview of each of these components is provided.

Impacts of a daily trap check law on the California ADC program

Effective January 1, 1990 California law required that all steel-jawed leghold traps be inspected at least daily and all animals in such traps be removed. The inspection and removal could be performed by the individual who set the traps, the landowner, or an agent of either. Prior to the passage of this law, California Animal Damage Control (ADC) personnel were exempt from Department of Fish and Game trap checking regulations. The data suggest that a decrease in trap use occurred after the implementation of the daily trap check. Where the program could effectively substitute other control tools or methods for the leghold trap, impacts to cooperators serviced and coyotes taken per unit of effort were minimal.

Norway rat infestation of urban landscaping and preventive design criteria

Fifty-four landscaped areas in downtown Boston were surveyed for Norway rat (Rattus norvegicus) activity. Each location also was characterized based on size, types of plantings, density of plantings, type of mulch, and sanitary and maintenance conditions. Factors most associated with the presence of rats were dense contiguous stands of shrubbery (e.g., needled evergreens) and refuse/litter availability on the ground. Design criteria should include effective spacing of shrubbery, limiting mass plantings of dense shrubs, selection of plant varieties that grow with openness underneath, strategically-placed and rodent-proof refuse containers, and use of crushed-stone inspection strips. Rodent control should be considered when landscapes arc designed, and proper maintenance of landscaped areas should be part of urban rodent control programs.

The potential impact of introduced commensal rodents on island flora

The impact of introduced commensal rodents on island flora has been relatively little studied compared with their impact on the fauna. The effects on vegetation composition, regeneration, and decomposition are largely unknown, but potentially great. Preliminary studies were carried out in the Galapagos Islands between 1993 and 1994 on the diet of introduced rats, Rattus spp. and feral house mice, Mus musculus, seed recovery rates and subsequent germination rates of seeds. R. rattus diet was primarily vegetation and 48% of rats had seeds in their stomachs. Significant differences were found between body size and overall contribution of both vegetable and animal foods, larger rats eating proportionately more animal foods and less vegetable. There was no significant difference between the sexes in terms of main dietary components. There was no significant difference in the selection of food types between R. rattus and R. norvegicus, both species tended to prefer banana and avocado, and only rats from the Miconia zones showed a preference for Miconia berries. No intact seeds were found in the stomachs of feral house mice from the same sites. Recovered seeds of two native and two introduced plant species were successfully germinated under laboratory conditions. R. norvegicus is potentially a better dispersal agent for seeds as it has a greater tendency to ingest them intact. The implications of these findings for the conservation of island flora are discussed.

The distribution and significance of anticoagulant-resistant Norway rat (Rattus norvegicus) in England and Wales, 1988-95

Between 1988 and 1995 populations of rats on agricultural premises were sampled to investigate the distribution of anticoagulant-resistant rats in England and Wales. In total, approximately 1,670 rats from 115 locations were tested for resistance to warfarin. Rats that were warfarin-resistant were subsequently tested for resistance to difenacoum, and since 1991 for resistance to bromadiolone. In some cases rats were also tested for resistance to brodifacoum, and in 1995 for resistance to flocoumafen. The results of these tests showed that there was a high prevalence of resistance to the first-generation anticoagulant, warfarin, in several regions of England and Wales. Rats from most populations sampled since 1991 appeared to be more resistant to bromadiolone than difenacoum, but in central southern England there were some populations where the reverse was true. In this same part of the country there was a relatively small focus where the rats had high degrees of resistance to several anticoagulant rodenticides. There was little evidence of resistance to brodifacoum or flocoumafen. The data are discussed with respect to the impact of anticoagulant rodenticide resistance on control of rats in the United Kingdom.

Plant secondary chemicals as non-lethal vertebrate repellents

Few effective repellents are currently available for the non-lethal management of vertebrate pests. This is perhaps not surprising considering the ad hoc nature of past applications which assumed that the target pest species would have the same attraction/aversion preferences as man. A more rational approach is to identify compounds that have real biological significance for the pest species. Plants have evolved an array of defense chemicals (secondary plant compounds) that inhibit the feeding of vertebrate herbivores, because they are either innately aversive or they generate a conditioned aversion. These compounds are, therefore, ideally suited for use in the reduction of feeding damage to crops, forest plantations and stored food products. Several of these novel plant-derived materials (e.g., cinnamamide) are already undergoing commercial evaluation. This approach facilitates the use of a number of systems to increase a plant's resistance to attack: topical application of the defense compound, systemic stimulation of the plants own resistance mechanisms and genetic enhancement. The two latter systems will enable the utilization of potent repellents that are not commercially viable for topical application and to concentrate their expression in the most palatable and vulnerable tissues. This paper also discusses work undertaken to improve our knowledge of the feeding strategies of target species. A proper understanding of these behaviors is essential before it will finally be possible to predict the field conditions under which a repellent will be effective.

Improved sealants for M-44 cyanide capsules

The M-44 sodium cyanide ejector is one of the most important tools used by the Animal Damage Control (ADC) program to protect livestock from coyotes. Unacceptable performance of M-44 cyanide capsules due to inadequate seals stimulated research to develop a better capsule sealant. Comparative tests of crude beeswax, Scheel SC-100 wax, and other materials revealed that capsules sealed with SC-100 were most resistant to deterioration in adverse environments. Based on these results, SC-100 wax was selected as the sealant of choice. Beginning in April 1989, all M-44 capsules made for ADC program use have been sealed with SC-100 wax. Since that date, the average number of capsules sold annually for ADC use is 15% lower than it was before 1989 even though the numbers of coyotes taken by M-44s each year has nearly doubled. The improved sealant appears to have increased the service life and effectiveness of M-44 cyanide capsules.

How to control a pest's pest -- flea and rodent efficacy

Fleas have caused health and sanitation problems for centuries. Most rodents are hosts to fleas. Baker Crop Protection Chemicals (BCPC) recently entered the rodenticide market (via SLN) with an efficacious fumigant for single burrow rodents, MAGNACIDE® H Herbicide/Rodenticide (a.i. acrolein). Noting that most burrowing rodents are flea infested, BCPC undertook an experiment to determine if fleas also succumb to acrolein under simulated field treatment scenarios. Results of the study under laboratory conditions demonstrated that fleas do succumb to acrolein treatments as well as the specific rodents targeted for treatment. This study also established rodent death rates from exposure to acrolein in a simulated closed system at 4 to 6 minutes, at a treatment rate of 20 milliliters.

The use of tip traps to control rabbit damage in Scotland

The factors affecting efficient use of tip traps to control rabbit populations were investigated in a series of field experiments. It was found that continual trapping at the same location was much less effective than periodic trapping. Night-time trapping operations produced larger catches of rabbits than day-time trapping. Traps were equally effective whether sited on existing runs through rabbit proof fences or on previously unbreached sections of fence. The sex ratio of rabbits caught was examined at four different locations and, in each instance, more females were caught than males. The installation of a network of tip traps and associated rabbit proof fencing on a study farm in southern Scotland provided a small positive income per rabbit when carcasses were sold to a local game dealer. Traditional trapping methods employing a professional trapper on the same study farm resulted in a large reduction in rabbit numbers, but despite the sale of carcasses to a local dealer, there was still a net cost to the farmer per rabbit caught. The catch time per rabbit using tip traps was considerably less than the catch time per rabbit using a professional trapper.

Effectiveness of Vichos non-lethal collars in deterring coyote attacks on sheep

Vichos non-lethal collars containing 45 to 105 ml of 3% capsicum oleo resin were evaluated as deterrents to coyote attacks on sheep. Each of five coyotes tested made neck/throat attacks on one collared lamb; four punctured collars and one pulled the collar from a lamb without puncturing it. One coyote did not resume biting the lamb for 60 min; it was retested two and four days later. At two days, the coyote punctured a second collar and briefly halted its attack. At four days, the coyote attacked a third collared lamb but made no attempt to grasp the neck/throat area. In tests resulting in collar punctures (n=5), coyotes immediately stopped their attacks and showed obvious signs of oral irritation; however, attack behavior resumed shortly thereafter (mean= 17 .6 min). Coyotes resuming attacks directed them toward the sides and rears of lambs. The Vichos collar is unlikely to prove effective in controlling coyote predation on sheep.

Techniques and expertise in wildlife damage control: A survey among the national animal damage control association (NADCA) membership

The membership of the National Animal Damage Control Association (NADCA) was surveyed during 1995 to collect information about specialty fields, preferred methods and experience. Respondents had broad experience that included 44 species or species groups. Members reported firsthand experience with an average of 17.6 different species and 2.9 vertebrate groups. Forty-three percent indicated that their specialization was among carnivores. In this group, coyotes, Canis latrans (45%), raccoon, Procyon lotor (23%) and skunk (13%) were most frequently mentioned. Members reporting carnivore experience had firsthand experience with an average of five different species. Rural and urban members did not significantly differ in breadth of experience with carnivores. Respondents most frequently specialized with coyote (11.8%), raccoon (11.5%), beaver, Castor canadensis (9.6%) and tree squirrel, Sciurus spp. (6.8%). Trapping was the most used technique for most mammals. Exceptions were deer or elk where exclusion was preferred. Blackbirds and starlings, Sturnus vulgaris, were most often controlled by repellents or scare tactics. Removal of an animal was the most common and preferred method and represented about 70% of responses for first choice.

Assessment of the environmental impact of brodifacoum during rodent eradication operations in New Zealand

Although Talon® baits containing brodifacoum have been used successfully in eradicating rats from some of New Zealand's offshore islands, little is known about any environmental effects of this toxin. Invertebrates, blackbirds, soil, and water at intervals of two days to nine months were sampled to determine whether brodifacoum residues were present after aerial distribution of Talon 20P cereal pellets on Red Mercury Island and after bait-station use of Talon 50WB wax-coated cereal blocks on Coppermine Island. No brodifacoum residues were found in soil, water, or most (99%) invertebrate samples. Low concentrations (0.12 µg/g) were found in one sample of slugs collected two days after aerial sowing. Liver tissues from all birds (n=4) and rats (n=3) found dead, and from all six birds collected alive eight months after aerial baiting, also contained low-to-moderate concentrations of brodifacoum (0.004 to 11.0 µg/g). These preliminary results suggest that invertebrates are not likely to accumulate brodifacoum as a result of Talon baiting. Laboratory studies showed that, although some invertebrates may eat Talon baits, it appears that the brodifacoum is metabolized and/or excreted within a few days. The dead blackbirds found were, therefore, more likely to have been killed by primary rather than by secondary poisoning. Further monitoring for brodifacoum residues after Talon operations should be undertaken to confirm that contamination of invertebrates, soil, and water is unlikely. Some bird species may be at risk from eating Talon baits. Likely effects on population levels of such species should be assessed to help weigh the risk and benefits of Talon use in rodent eradication.

The evolution of APHIS' two gas cartridges

The U.S. Department of Agriculture, Animal and Plant Health Inspection Service (APHIS) has two federal (Section 3) vertebrate pesticide registrations with the U.S. Environmental Protection Agency (EPA) for gas cartridges to control damage to American agricultural resources and reduce threats to public health and safety. The gas cartridges are pyro-fumigant devices that produce primarily carbon monoxide when ignited. In sealed burrows or dens, carbon monoxide is highly toxic when inhaled, leading to tissue hypoxia. Carbon monoxide is recommended by the American Veterinary Medicine Association's panel for euthanatizing animals because it quickly induces unconsciousness without pain and with minimal discernible discomfort. APHIS's gas cartridges for rodent and predator control have been developed and maintained primarily by research conducted at the Denver Wildlife Research Center (DWRC). APHIS's Gas Cartridge (EPA Reg. No. 56228-2) for burrowing rodent control has evolved through various formulations and sizes. Formerly, the Gas Cartridge was formulated with six-active ingredients; however, in April 1996, an amendment to use only two-active ingredients [sodium nitrate and charcoal (carbon)] and two-inert ingredients (fuller's earth and borax) was approved by EPA. These two-active ingredients produce carbon monoxide, and the inerts increase the burn time. DWRC field studies have shown the gas cartridge to be effective for the control of rats, woodchucks and Richardson's ground squirrels, but not for Northern pocket gophers. The Large Gas Cartridge (EPA Reg. No. 5622821) was originally developed using only two ingredients (sodium nitrate and charcoal) as a predacide to control coyotes in dens. Recent efficacy data led to the addition of the fox and skunk to the label; however, the Large Gas Cartridge was not effective in controlling badgers. This paper discusses the evolution of APHIS's gas cartridges and includes: 1) an introduction to APHIS's gas cartridges; 2) a synopsis of gas cartridge research conducted by personnel of the Denver Wildlife Research Center; and 3) a discussion of the management implications associated with the current status and future of APHIS's gas cartridges.

Results of a non-lethal survey and report provided to the New Mexico legislature

Social and political pressures affect decision making regarding wildlife damage management issues tremendously. In fact, these areas are included in the Animal Damage Control decision model outlined in the programmatic Environmental Impact Statement. Growing concern regarding pain and suffering of animals trapped by ADC Specialists prompted two actions by the 41st Legislature of the State of New Mexico in 1994. The legislature directed New Mexico ADC not to spend over three-quarters of its $304,000 appropriation on lethal methods. The legislature also passed a memorial bill requesting the New Mexico Department of Game and Fish, in cooperation with the U.S. Fish and Wildlife Service, and Animal Damage Control, to prepare a report with recommendations on noninjurious methods for controlling wildlife damage to private property. In response, the report was prepared and ADC employees in New Mexico conducted a survey of cooperators to determine what non-lethal methods they had implemented. Over 1,300 active agreements were surveyed to determine what non-lethal methods had been tried, what it cost to implement those methods, which methods were successful, why some methods were discontinued, and whether lethal methods were also used to reduce agricultural and other property losses. Survey results, the report on noninjurious methods, and a fiscal account of state appropriations spent on non-lethal methods was provided to New Mexico legislators during the 1995 session.

Managing plague in endangered species habitats

Plague is an endemic disease among field rodents in the southwestern United States. Epizootic outbreaks of this disease increase the risk of human infection where man comes into contact with infected rodents or their fleas. The risk is further increased when colonial rodents are involved, since these animals are usually found in large numbers and are often found in locations where people live, work, or enjoy recreational activities. Elimination of large numbers of susceptible rodents from a particular location following a plague epizootic usually results in a quiescent period when plague is neither a threat to those rodents moving into the former colony confines or a threat to people using the same geographic area. In areas where the human health threat following an epizootic is unacceptable, susceptible rodents and their fleas may be eliminated through trapping or poisoning the animals and dusting the burrows with insecticide to kill the fleas. In recent years, however, the health (or death) of prairie dogs (Cynomys spp.) or California ground squirrels (Spermophilus beecheyi) has become a significant ecological issue in areas where these rodents are the predominant prey base for endangered species of animals. Prairie dogs often support populations of endangered raptors while California ground squirrels may support the endangered San Joaquin kit fox (Vulpes macrotis mutica). In some areas of central California, where the kit foxes are supported by ground squirrels, reduction in the number of rodents to reduce the threat of plague is prohibited. Confounding the management of plague, limitations may be placed on the types of insecticides used for flea control following an epizootic. When insecticide use is permitted, preventive flea control to protect rodents from plague results in a continuous, sustainable population of highly plague susceptible rodents. When flea suppression fails, replacement animals can be trapped and relocated to areas decimated by plague. Not only are these types of plague management expensive in terms of manpower, equipment and time, but the potential of epizootic plague is constantly present.

Operational control of the brown tree snake on Guam

An operational control program for brown tree snakes (Boiga irregularis) on Guam began in April 1993. The program focused on minimizing the dispersal of brown tree snakes to other Pacific islands and the U.S. mainland. During the first year of operation, more than 3,000 snakes were caught within a kilometer of high risk port facilities using traps, detector dogs, and spotlighting. Additionally, habitat modifications and prey-base removal were used to reduce the attractiveness of these facilities to brown tree snakes. Public awareness was also an important part of the program such as the education of cargo packers, shippers, and Customs inspectors who could further minimize brown tree snake dispersal off-island. Initial control efforts in the program became more efficient with the recognition of brown tree snake characteristics, i.e., it was discovered that perimeter trapping a 5 ha patch of jungle was sufficient to remove most snakes instead of saturating the area with traps.

Reducing livestock depredation losses in the Nepalese Himalaya

In the Nepalese Himalaya conflict with rural communities due to livestock predation to large carnivores like snow leopard, common leopard, wolf and wild dog has risen sharply in recent years. This increase is attributed to a number of factors, including implementation and enforcement of wildlife protection laws (which have permitted a recovery in carnivore numbers), the creation of protected areas (which serve as refuges from which predators can populate the surrounding area), the depletion of natural prey due to poaching and loss of habitat, and lax livestock herding practices. However, little information is presently available upon which to design remedial programs. U.S. AID provided research funding for an in-depth assessment of snow leopard predation in the Annapurna Conservation Area (ACAP), a new innovative approach to nature conservation. Baseline information on livestock numbers and mortality were gathered during household interviews, followed by field surveys to assess animal husbandry systems, map pastures, establish periods of use and estimate stocking rates, and to characterize habitat using randomly located plots. Data substantiate the existence of depredation "hotspots," where high loss occurs, in some cases exceeding 14% to 20% of the livestock population over a short period. Losses varied seasonally, and from year to year. Small-bodied stock like goat and sheep were more vulnerable than large-bodied stock like yak, although horses were especially vulnerable. Factors most closely associated with predation included lack of guarding (or very lax supervision), especially during the daytime, and repeated use of pastures where livestock depredators were known to be actively hunting. Herders usually reacted to repeated depredation incidents by attempting to trap or shoot the suspected culprit until losses declined to an acceptable level. As large carnivore populations become increasingly fragmented and genetically isolated, new management strategies are urgently needed, especially within the buffer zones and intervening corridors between separated parks and reserves. People reside within nearly all Himalayan protected areas, and such issues as loss of livestock and competition between wildlife and livestock cannot be avoided. A plan is offered for alleviating livestock loss in the Annapurna Conservation Area that involves local institutions in decision-making, rewards sound husbandry practices, strengthens indigenous institutions, without further eroding ACAP's unique biological diversity and diverse carnivore population. The authors believe these measures and ideas could be fruitfully extended to other parts of the Himalaya.

Animal rights and the need to understand nature; A debate

The author summarizes his opposition to the "animal rights" movement, describing what he terms "nature's life-death ethic." He defends the use of domestic animals in agriculture and appropriate regulation of sport hunting, arguing that animals killed intentionally by humans die a much more humane death than wildlife that die of natural causes such as predation, disease, or starvation. He states his belief that people have a moral obligation to manage nature once they have disrupted it.

Animal liberation and the lessons of nature

The author states that “animal liberation” and “animal rights” have been misunderstood. He describes what he believes to be the basis of the animal liberation movement, relying on philosophical and moral grounds. He clarifies that animal liberation seeks neither to extend to animals the same set of rights enjoyed by humans nor to deny that human life can have greater moral worth than animal life. He concludes by explaining the ways in which scientific knowledge of natural entities, processes, and organizations is and is not relevant to animal liberation.