Skip to main content
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:

Salmon, Terrell P. 2012. VPC: Fifty Years of Progress? Proc. Vertebr. Pest Conf. 25:3-6.

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.


A vision for wildlife management

My vision that vertebrate pest control is applied ecology has come a long way since my first field baiting for rats in 1939. Three events are especially important. First, the Vertebrate Pest Conferences were established to provide published information and exchange of views about animal control. Second, on December 19, 1985, the Denver Wildlife Research Center, in the Department of Interior, was transferred to the Department of Agriculture and became the National Wildlife Research Center. Third was when the Wildlife Management Institute finally allowed The Wildlife Society to hold separate annual meetings. This led to the Society recognizing the ecological importance of animal damage control in human-modified environments where the outcome must be managed-not left to nature.

A national review of the status of trapping for bird control

We examined the status of trapping to control bird damage based on a nation-wide questionnaire, literature, and on-site visits of trapping programs. We mailed 464 questionnaires to Agriculture Commissioners in California, Cooperative Extension Wildlife Specialists, USDA APHIS Wildlife Services personnel, state Department of Agriculture personnel, and members of the National Animal Damage Control Association. Two hundred fifty questionnaires (54%) were returned from 50 states, 1 territory, and 51 California counties. Fifty-four percent of the respondents indicated they either trap, monitor, or provide information on bird trapping. Regarding specific activities, 49% actively trapped while 43% provided information only. By affiliation, 90% of private respondents trapped, followed by 60% of federal respondents. Respondents listed 53 species of birds causing damage. Cited most often were rock doves (Columbo livia), European starlings (Sturnus vulgaris), blackbirds, Canada geese (Branta canadensis), American crows (Corvus brachyrhynchos), house finch (Carpodacus mexicanus), and house sparrows (Passer domesticus). Respondents listed 52 crops, 18 types of animal production facilities, and 16 non-crop sites that were subject to bird damage. Respondents listed 25 species that were trapped. Modified Australian crow traps, walk-in traps, and drive traps were used most frequently. Most respondents (80%) rated trapping as moderate to excellent for ducks, geese, rock doves, and house sparrows. Trapping for starlings was rated as moderate to excellent by 75% of private industry respondents (mostly non-agricultural damage), but 80% of California county returns (dealing mostly with agricultural damage) rated it as slight. Differences in control ratings for some species related to the type of damage site, geographic location, and organizational affiliation. Most (57%) respondents felt trapping was not important in overall bird control in any crop. California Agriculture Commissioners (>70%), however, indicated trapping was important for starling and house finch control, particularly in grapes. Most respondents (71%) felt trapping for bird control stayed at the same level or increased since 1990, and 82% thought it would stay the same or increase in the future. This sentiment was strongest among respondents from private industry (93% ). We identified literature on general trapping concepts, specific traps, trapping techniques, and operational trapping programs. We found no rigorous evaluations of trapping’s effectiveness or the factors influencing results. Three studies provided partial economic analyses, but most evaluations of trapping put emphasis on the numbers of birds caught rather than the amount of damage eliminated in relation to the cost of control. New trap designs or trapping strategies that may have application to current bird problems include the impact trap, the Modesto funnel trap, noose-covered wickets, glue-coated perches, decoy-crop trapping, trammel nets, and mist nets. We identified five California counties currently monitoring house finch trapping. From 1991 to 1995, an average of nearly 100,000 house finch have been trapped annually. Only Sonoma County currently traps with county personnel, taking an average of 1,000 starlings/year from 1991 to 1995. We conclude trapping for bird control: 1) is commonly used across the country by a broad segment of wildlife damage control practitioners; 2) is important for the control of selected species, such as starlings and house finch in California; 3) is important for bird control in certain crops such as grapes in California, and non-crop sites such as around buildings in urban areas; 4) will continue to be used at the same or increased levels in the future; 5) has not been rigorously evaluated from a cost-benefit standpoint; 6) can be improved with new trap designs and strategies; and 7) merits additional research.

Efficacy of the aerial application of methyl anthranilate in reducing bird damage to sweet corn, sunflowers, and cherries

Field trials using methyl anthranilate, formulated as Bird Shield® repellent, were performed by aerial applicators at one pint per acre on sweet com in Colorado, and sunflowers in North Dakota, and at one, two, and four pints per acre on cherries in Washington. Nineteen com fields ranging in size from 9 to 25 acres were treated twice, at five day intervals, prior to harvest and compared with six untreated fields during a two year study. During the same time period ten sunflower fields, along with their adjacent cattail marshes were treated twice, at seven day intervals when the birds began to feed on the ripening seed, and compared with six untreated counterparts. Five out of the six untreated com fields were unharvestable, with greater than 75% damage, because of the severe damage caused by the resident populations of red-wing blackbirds (Agelaius phoeniceaus). Nine of the treated fields sustained no damage at all. The damage in the remainder was contained at pre-treatment levels (4% to 20%). The two applications of the repellent were sufficient to move the resident population of blackbirds out of the sunflower fields with no substantial damage to the crop. Untreated sunflowers sustained 783 to 90% damage. Treated sunflowers sustained between 2.6% to 3.4% damage. The difference in seed weights between untreated and treated plots was significant (P=0.01) with a mean weight of 0.018 g/cm2 of seed per head within the former and 0.084 g/cm2 of seed per head within the latter. Harvest weights ranged from 133 to 700 lbs/ac (mean=344) in the untreated plots while weights ranged from 1430 to 1909 lbs/ac (mean=1675) in the treated plots. No adverse effects were noted with fish or resident populations of ducks. The application of the repellent by helicopter reduced bird damage from just under 13% in one untreated cherry orchard to between 0.08% and 1.0% seven days later with 1, 2, and 4 pints/ac rates in comparable orchards. Greater differences were encountered when the repellent was applied at two additional sites. When 2 pints/ac was applied, bird damage was limited to 8% after 15 days when the untreated block sustained between 58% to 68% damage.

Responses of blackbirds to mature wild rice treated with Flight Control bird repellent

Red-winged blackbirds (Agelaius phoeniceus) and other granivorous species cause substantial economic damage to wild rice in California. Currently available damage control techniques have only limited effectiveness and there is considerable need for new effective techniques. We conducted a field trial in northern California to determine the effectiveness of the bird repellent, Flight Control™ (50% anthraquinone), applied at rates of 18.6 and 55.8 L/ha, in reducing blackbird depredations to wild rice. We detected no effect of the treatments on blackbird behavior in the field, even though captive red-winged blackbirds were deterred in feeding trials with wild rice seeds collected from our study plot. We suggest several possible reasons for this: 1) blackbirds used wild rice for cover as well as a food source; 2) birds perhaps received insufficient exposure to the repellent owing to either the birds’ ability to hull the seeds rapidly, low anthraquinone residues on the seeds, and/or non-uniform coverage of seed heads; 3) although Flight Control™ is a feeding deterrent, an aversive response might require repeated exposure to treated rice; and 4) frequent turnover in the depredating population would result in birds not being present long enough to acquire an avoidance response. Clearly, a better understanding of blackbird movements and behavior in wild rice is needed to develop an effective management strategy.

Bird and small mammal use of mowed and unmowed vegetation at John F. Kennedy International Airport, 1998 to 1999

We evaluated bird and small mammal use of two mowed (15 to 25 cm height) and two unmowed vegetation plots (40 to 88 ha) at John F. Kennedy International Airport (JFKIA), New York, in 1998 to 1999 to determine which management strategy would best reduce wildlife use of the airport. We counted more birds per 5- minute observation period in unmowed plots than mowed plots in both 1998 (9.0 versus 7.9) and 1999 (11.7 versus 8.6). Maximum vegetation height was greater (P<0.05) for unmowed areas than mowed areas after mowing commenced in 1998 and 1999 for each two-week monitoring period. In 1998 to 1999, vegetation density was also higher (P<0.05) for unmowed plots for 13 of 14 sampling periods. The species composition of vegetation differed (X2=20.54, df=3, (P<0.01) among mowed and unmowed plots. Mowed plots contained a higher percentage of grasses (81% versus 68%), and a lower percentage of forbs (16% versus 25%) and woody plants (1% versus 4%) than unmowed plots. Vegetation was generally sparse in both unmowed and mowed plots, a consequence of the poor, sandy soils on much of the airport. We captured 33 small mammals from three species in unmowed plots and 12 individuals of one species in mowed plots in 1999. Small mammal populations increased seasonally in unmowed plots, but remained constant in mowed plots over the same time period. We recommended JFKIA switch from the unmowed vegetation management regime in place since 1986 to a regime of maintaining vegetation mowed at 15 to 25 cm height. This management strategy should reduce bird and small mammal use of grassland areas at JFKIA. Further research should examine use of alternative vegetation types to improve ground cover and vegetation density at JFKIA while minimizing attraction to wildlife.

Birds and aircraft: fighting for airspace in crowded skies

Birds and other wildlife such as deer (Odocoileus spp.) pose increasing economic and safety concerns to aviation interests in the USA. Civil aircraft collisions with wildlife (wildlife strikes) annually reported to the Federal Aviation Administration (FAA) increased from about 1,700 in 1990 to 4,500 in 1999. Waterfowl (Anatidae), gulls (Larus spp.), raptors (Accipitridae, Pandionidae, Cathartidae, Falconidae) and deer were involved in 80% of the reported strikes in which aircraft were damaged. Wildlife strikes caused annual losses of $300 million to civil aviation, 1990 to 1998. The known number of civil aircraft destroyed as a result of wildlife strikes in the USA increased from four in the 1960s to 22 in the 1990s. The number of airports requesting assistance from the U.S. Department of Agriculture’s Wildlife Services program increased from about 42 in 1990 to 363 in 1999. Attendance at annual Bird Strike Committee USA meetings increased from 10 people in 1990 to over 300 in 1998-1999. Four factors have synergistically interacted to increase the problem of, and interest in wildlife strikes in the past 20 years. First, populations of many species hazardous to aviation have increased and adapted to urban environments such as airports. Second, passenger enplanements and commercial air traffic (landings and takeoffs) have increased at annual rates of about 4.2% and 2.6%, respectively, from 1980 to 1998. Third, modern two-engine turbojet and turbofan aircraft are generally less apparent to birds because these aircraft are faster and quieter than older aircraft. Finally, liability issues related to wildlife strikes are increasing for airport operators and others. The National Transportation Safety Board issued nine recommendations to the FAA in November 1999 that, if implemented, should reduce the threat of wildlife strikes. These recommendations included more research in methods of repelling birds from airports, use of radar to warn pilots of bird concentrations, development of wildlife hazard management plans for airports, mandatory bird strike reporting with better identification of species which are struck, and improved interagency cooperation in issues involving aviation and wildlife.

Comparison of pyrotechnics versus shooting for dispersing double-crested cormorants from their night roosts

Roost dispersal using pyrotechnics has been an effective program for reducing serious cormorant predation problems at catfish farms in Mississippi. Under a recent cormorant depredation order, catfish farmers are also allowed to shoot cormorants at their farms, but not at roosts. To potentially enhance cormorant roost dispersal programs and obtain data about shooting in roosts, I compared pyrotechnics versus shooting for dispersing cormorants from their night roosts. Five pairs of roosts were sequentially selected based on their similarity in numbers of birds and area occupied. By random selection each roost in the pair was harassed simultaneously using either pyrotechnics (screamer sirens and bird bangers) or shooting to kill with steel shot. Harassment of each roost took place during 1.5 hours before sunset and continued for up to three nights to disperse > 90% of the birds from the site. During harassment efforts we recorded the number of pyrotechnics and shotgun shells used as well as the amount of time of actual harassment. We then monitored each roost for up to 10 days to assess how quickly birds returned to these sites. We found no difference (P>0.05) between treatments in the amount of time and shells used to disperse cormorants from their night roosts, or in the number of days post-treatment until birds returned to these sites. However, fewer shotgun shells (mean=286.6, SE=46.56) than pyrotechnics (mean=429, SE=81.3) were generally used. Despite deploying only skilled marksmen to shoot cormorants in roosts, relatively small numbers (mean=45.4, SE= 11.14) of cormorants, comprising <5% of roosting populations were killed during consecutive nights of harassment. I conclude that shooting is at least equally effective as pyrotechnics for dispersing cormorants from their night roosts and if included under the cormorant depredation order is unlikely to result in a large number of birds killed.

Evaluating relocation as a vulture management tool in north Florida

As distributional patterns of black vultures (Coragyps atratus) and turkey vultures (Cathartes aura) change, and as woodland habitat declines, vultures increasingly come in contact with human activity. Relocation of problem birds is one potential management approach for resolving conflicts. Relocation involves trapping and moving the vultures some distance away where their subsequent behavior is not expected to conflict with human activity. To evaluate vulture responses to relocation, we trapped and patagial-tagged 114 vultures at two roosting areas over a period of ten months and equipped ten of them with satellite transmitters. Of 9,101 locations, 18.6% had a measure of accuracy of 1000 m to <150 m. The remainder had an accuracy of >1000 m of accuracy (n=3149), no estimate of location accuracy (n=2024), or invalid location (n= 1117). Two transmitters were recovered due to removal or illness of the bird, were reset, and deployed on different vultures. Sixteen tagged birds were sighted after their release. Half of the sighted birds were observed at their unmodified trap site, and four of eight birds with transmitters were tracked to within 16 km of their trap site. No birds have been tracked to or seen at the modified trap site. One bird was tracked to within 32 km of its modified trap site. Birds took an average of eight months to return to the trap site. Relocation appears to be effective in the short term, but habitat modification and harassment to render the location unattractive is necessary for successful long-term removal of problem vultures.

Capture and telemetry techniques for double-crested cormorants (Phalacrocorax auritus)

Double-crested Cormorants (Phalacrocorax auritus) often roost in cypress oxbows and nest on islands making their capture for research studies difficult. In the southeastern United States we used a capture technique involving a boat equipped with flood lights, flushing the birds out of their roost trees, and capturing them with a landing net. On the Great Lakes we devised a capture technique using modified padded leg-hold traps placed in nest trees or on the ground in the colony. We captured >250 cormorants using these two techniques with very few injuries to the birds. In a study with captive birds, we evaluated the short-term effects of backpack and patagial tag VHF transmitters and their attachment techniques for use on cormorants. We conclude that backpack VHF transmitters are applicable for use on double-crested cormorants and that patagial solar powered transmitters should be further tested. We also tested two methods for simultaneously attaching a VHF transmitter and a backpack satellite transmitter to cormorants. Birds with the VHF patagial tag attachment showed moderate to heavy feather wear and abrasions on the ventral surface of the patagium. We recommend gluing the VHF transmitter to the backpack satellite transmitter for attaching both VHF and satellite transmitters to double-crested cormorants. These adaptable cormorant capture and telemetry techniques should prove suitable for use in other habitats and situations.

Wild turkeys and agriculture damage: Real or perceived thresholds and tradeoffs

Wild turkey (Meleagris gallopavo) populations have been restored and enhanced through introductions and reintroductions in 49 of the 50 states to huntable populations within the last 30 years. Populations are presently estimated to exceed 4 million birds within the United States. In many states, wild turkey habitat includes woodlots interspersed with agricultural lands, and some of the highest known population densities of wild turkeys are found in such areas. This paper will report on existing research, examining perceived versus actual damage caused by wild turkeys. It will also provide information based on a recent survey of biologists from the State Fish and Wildlife Agencies, State Cooperative Extension Service wildlife specialists, and USDA-APHIS/Wildlife Services personnel across the United States who receive reports of both perceived and actual damage by wild turkeys to a diversity of agricultural crops. It will attempt to: examine the human dimensions aspect of landowners and managers toward thresholds of tolerance; the economic and recreational user benefits of maintaining high populations of wild turkeys, which utilize a diversity of habitats including agricultural lands; and the values placed on recreational use and enjoyment of the wild turkey resource. It is expected that future interactions between wild turkeys and agricultural crops will continue as will efforts and alternatives to prevent damage, explore the tradeoffs, and resolve potential conflicts for the benefit of agricultural producers and the wild turkey resource.

Natural resources management and the bird aircraft strike hazard at Westover Air Reserve Base, Massachusetts

Bird-Aircraft Strike Hazard (BASH) reduction strategies at Westover Air Reserve Base (ARB) conflict with recommended habitat management strategies for two state-listed grassland bird species that inhabit the Base-the upland sandpiper (Bartramia longcauda) and the grasshopper sparrow (Ammodramus savannarum) . Westover ARB contains the largest contiguous grassland habitat in the New England region, comprising 1,600 acres that surround the airfield. Annual breeding surveys, emphasizing the upland sandpiper and grasshopper sparrow, began in 1986. Initial surveys revealed that the implementation of habitat management suggestions provided by the Massachusetts Division of Fisheries and Wildlife (MDFW) resulted in a rapid rise in specie population levels. More recent surveys suggest that population levels stabilized as the habitat reached carrying capacity. State habitat management guidelines recommend prohibition of pedestrian and vehicle movement through the breeding grounds from April 20 through August 1. These guidelines conflict with U.S. Air Force (USAF) BASH reduction guidelines, which require mowing to reduce the attractiveness of the airfield to the overall grassland bird population. Conflict resolution efforts involving the installation, the USAF BASH Team, the U.S. Department of Agriculture-Wildlife Services, and the MDFW have produced limited success. However, an airfield Vegetation Management Plan has been developed in conjunction with these agencies to reduce the attractiveness of the grassland habitat to species that pose the greatest threat to aircraft safety (e.g., wild turkey, white-tailed deer, and gulls). Westover ARB personnel continuously monitor and modify management practices to reduce the BASH threat and also to maintain suitable habitat for sensitive grassland bird species on the Base.

Controlling gulls at landfills

In spite of significant progress toward the application of recycling and other waste minimization processes, active landfills are expected to remain a common feature on the landscape for the foreseeable future. The availability of food and habitat at landfills will continue to act as a catalyst for a variety of human-wildlife conflicts. In this paper, we will focus specifically on on-site and off-site conflicts and management alternatives to resolve conflicts associated with gulls at landfills. Case histories of gull damage management programs conducted by Wildlife Services will be presented to illustrate the effectiveness of control strategies adapted to meet site-specific management objectives at landfills in the northeastern United States.

Effective dispersal of birds from buildings and structures by fogging with Rejex-it® TP-40

Fogging of Rejex-it® TP-40 offers an efficient method for the management and dispersal of nuisance birds from many areas. The amount of the methyl anthranilate (MA) based repellent is greatly reduced over any other application method. The method is direct and is independent of the activity of the birds. Application with any aerosol generator, thermal or mechanical, that can deliver droplets of less than 20 microns, has been shown to be very effective. The operation can be manually or fully automatic and pose only minimal risks to operators or animals. All birds that became a nuisance and safety problem in the hangars and warehouses of TWA and AA at LaGuardia and Newark were successfully driven out by fogging Rejex-it® TP-40 with a thermal fogger. Applications in a dairy barn, a dry boat storage, on a pipe rack, and electric substation all have also been demonstrated to be very cost effective and long lasting without killing a single bird.

Cormorant research and impacts to southern aquaculture

Several North American waterbird species were negatively affected by compromised environmental quality by the mid-twentieth century. Double-crested cormorant populations responded to increased environmental regulations in the United States in the early 1970s. The abundance of cormorants wintering in southern states (especially Alabama, Arkansas, Lousiana, and Mississippi) increased concurrently with a marked increase in catfish, crawfish, and bait fish production in these states since 1980, thus increasing regional concern regarding production losses to these industries. Cormorants wintering in Mississippi have increased nearly 225% since 1990. Food habit studies, bioenergetic predictions, and captive-bird foraging experiments indicate that individual cormorants consume approximately 0.5 to 0.7 kg (1 to 1.5 pounds; i.e., about 10 fingerlings) of catfish fingerlings per day. Although no present management techniques permanently redistribute cormorants, dispersal of night roosts remains the most effective method to temporarily deter cormorants from primary aquaculture areas. Ongoing investigations will improve our understanding of cormorant impacts to catfish production, and the annual movement patterns and population biology of North American cormorants. Given concerns regarding cormorant impacts to commercial and recreational fisheries in the United States, management objectives should highlight minimized impacts to economic and recreational opportunities, rather than target populations of breeding and/or wintering double-crested cormorants.

Home ranges and habitat selection of white-tailed deer in a suburban nature area in eastern Nebraska

We evaluated the movements of 59 radio-collared female white-tailed deer (Odocoileus virginianus) at the Gifford Point Wildlife Management Area (GP) and Fontenelle Forest Nature Area (FF) in eastern Nebraska from 1994 to 1997. Annual home ranges averaged 276 ha (CI= 166 ha). Forty-four of the deer maintained relatively small home ranges (0= 129 ha) and resided in the GP lowlands (n=14), FF lowlands (n=11), and FF uplands-Bellevue residential area (BR) (n=19). Deer in the latter area were frequently observed in backyards, at deer feeders, and on city streets. Seven of the deer were transients, maintaining seasonal home ranges that varied in size and did not overlap in location. The centers of these seasonal home ranges were on average 2,430 m apart. No consistent patterns of dispersal or seasonal migration were detected. Deer response to hunter activity was highly variable. Most deer maintained relatively static home ranges before, during, and after the hunting seasons, but three deer moved over 2,000 m and established non-overlapping home ranges after the hunting seasons. Since no migration patterns were observed, we suggest that regulated hunting seasons continue in both the upland and lowland areas of GPFF, and in the open space areas of Bellevue where conditions are conducive to hunting.

A comparison of physical, chemical, and genetic controls to reduce deer browse damage to hybrid poplar seedlings

Deer browsing on commercially-grown hybrid poplar seedlings can inflict heavy damage to trees and reduce economic returns by deforming and/or stunting the growth of trees. A field trial was initiated on a 7,050 ha hybrid poplar plantation to evaluate the effectiveness of a physical barrier (Vexar tubing), a topical repellent (Plantskydd), a systemic repellent (SeO2), and a less-palatable clone in reducing deer browse damage. The trial was conducted during the 1999 growing season in a recently harvested and replanted 6 ha unit. The four treatments were arranged along with a control in a randomized block design, with five blocks randomly arranged near the edge of the harvest unit where deer activity was concentrated. Terminal browse damage was assessed at two week intervals over a ten week period. Relatively little browsing occurred in any of the treatments during the first four weeks following planting. Vexar tubing provided superior protection (P<0.05) for seedlings at 6, 8, and 10 weeks following planting compared to all other treatments. The clonal treatment was browsed less (P<0.05) than the Plantskydd, selenium, and control treatments over the ten week evaluation period. However, overall growth rates for this clone were lower (P<0.05) than all other treatments, suggesting that this particular clone would not be beneficial from a fiber production standpoint. The results of this study suggest that Vexar tubing is an effective method of controlling deer browse damage to hybrid poplar seedlings. Use of genetically-resistant clones may provide some browse protection. However, growth rates of the clone tested did not perform well enough to consider using this clone on an operational basis.

Comparing the efficacy of delivery systems and active ingredients of deer repellents

Deer (Odocoileus spp.) occur across the United States and provide many desirable recreational and aesthetic opportunities. Unfortunately, deer foraging, particularly where population densities are high, can negatively impact agricultural resources or damage ornamental plants. Repellents are often regarded as a desirable approach to limit deer browsing. Although many products are marketed for use as repellents, the efficacy of these products in actually reducing deer browsing is varied. This paper reviews the results from efficacy tests we have conducted at the NWRC Olympia Field Station over the past several years as well as repellent work conducted by others. General efficacies of delivery systems and active ingredients incorporated in a variety of products are compared. Generally, products which have repeatedly demonstrated good efficacy in our trials are those products that produce sulfurous odors. These products have significantly reduced deer browsing for 8 to 12 weeks.

Deer population management through hunting in a suburban nature area in eastern Nebraska

The Fontenelle Forest Nature Area (FF) maintained a hands-off management policy for 30 years until it was recognized that white-tailed deer (Odocoileus virginianus) populations had grown to such levels that they were severely degrading native plant communities. In 1995, members of a community task force decided to sponsor annual nine-day hunting seasons on FF after learning that densities exceeded 28 deer/km2. Archers harvested 85 antlerless deer in the FF upland areas adjacent to residential Bellevue, Nebraska during 1996 to 1998. Muzzleloader hunters removed 53 antlerless deer from the FF lowland areas. Archery and muzzleloader hunters harvested 297 deer during the same period in Gifford Point (GP), a state-owned wildlife management area adjacent to the FF lowlands. Overall deer densities declined from 28 deer/km2 in 1995 to 14 deer/km2 in 1998. Densities were at or near over-winter goals in all areas by 1998, except for the unhunted residential area, which still maintained 20 deer/km2. Annual survival rates for radio-marked adult and yearling female deer were 0.70 and 0.59, respectively. Archery was the primary mortality factor (20%) for radio-marked deer across years. Population models predict that densities would increase to 55 deer/km2 in five years if hunting seasons were abandoned in FF. Hunter behavior in FF has been reported as excellent and little public opposition exists.

Observations on the contacts and home ranges of feral goats in relation to the spread of diseases of livestock

Many diseases of livestock, such as foot and mouth disease (FMD), rinderpest, pest des petite ruminants, and maedi-visna, are exotic to Australia and contingency plans are in place to counteract their introduction. Epidemic modeling fulfills a vital role in these plans. Feral goats occur at high density with livestock in the high-rainfall zone of eastern Australia. Contact within and between groups of domestic and feral ungulates contribute to the behavior of disease in sympatric populations, and are essential parameters for epizootic models. A project in central New South Wales, Australia is investigating the contacts and home range sizes of feral goats in order to construct models for FMD transmission. Preliminary analysis has shown that contacts between feral goats and sheep were fewer than between feral goats, and that the home ranges of goats in the study were small (<2.5 km2). This paper discusses: the home ranges of feral goats in different environments; the interactions between feral goats and sheep; the potential of feral goats to maintain and spread exotic diseases common to goats and sheep; and modeling of disease transmission between feral goats and sheep.

Attitudes towards rabies in southern Texas: a need for public education

An epidemic of canine rabies transmitted by coyotes (Canis latrans) began in 1988 along the Texas-Mexico border. The disease spread rapidly throughout southern Texas and resulted in two human deaths and >2,000 rabies exposures in which prophylactic treatment was required. To combat this epidemic, the Texas Department of Health conducted an oral vaccination program that targeted free-ranging coyotes and offered free immunization of pets. However, the latter program met with resistance from the public. We hypothesized that the general public lacked knowledge as to the seriousness and spread of rabies, which resulted in their apathy for taking precautionary measures. To test our hypothesis, we surveyed adult residents of the Lower Rio Grande Valley in Texas to assess their knowledge of rabies and to determine their reasons for lack of compliance with the pet vaccination law. We approached 560 adults (i.e., >21 years old) and asked them to take an oral questionnaire concerning their knowledge of rabies; response rate was 40% (223 out of 560). Mean score of respondents was 59% of the maximum possible score. Adults lacked general knowledge of rabies transmission and mortality. Although the majority (89%) of respondents knew that it was unlawful to own unvaccinated dogs and cats against rabies, only 23% (n=52) claimed to vaccinate their pets. Of those who responded that they regularly vaccinate their pets, 50% did it to promote pet health and the remaining 50% of respondents admitted to being fearful of repercussions if they did not obey the law. Reasons for not vaccinating pets included laziness (n=46, 27%), liability of claiming pet ownership (n=31, 18%), cost (n=29, 17%), lack of law enforcement concerning unvaccinated pets (n=26, 15%), unaware of rabies epidemic in area (n= 19, 11%), "dime-a-dozen" attitude [i.e., can always get another pet] (n=l5, 9%), and governmental conspiracy to locate illegal aliens in the United States (n=5, 3%). Educational programs are needed in the Lower Rio Grande Valley of Texas to increase the general public’s awareness and knowledge of rabies.

The epidemiology of a case of raccoon roundworm infection

The epidemiologic investigation of a recent case of cerebrospinal nematodiasis caused by the common raccoon intestinal roundworm (Baylisascaris procyonis) in an 11-month old child from Monterey County, California revealed a remarkable series of circumstances which led to the child’s infection. Human infection results from the inadvertent ingestion of eggs which are passed in large numbers (millions of eggs/day) in the feces of infected raccoons. Groups of raccoons typically defecate in common areas called latrines where the environmentally resistant B. procyonis eggs accumulate. Once infective-stage eggs are ingested, the immature larvae hatch and begin to migrate extensively and aggressively in tissues, frequently invading the spinal cord and brain. The one acre property where the child lived had extensive evidence of raccoon activity including 21 latrine sites. Fecal samples collected from the latrines and soil samples on the property were examined using concentration/flotation methods. All samples contained numerous embryonated B. procyonis eggs in both immature and fully infective larva stages. Unprecedented numbers of raccoons were observed living in the area and surrounding community. Further examination of the raccoon feces revealed that the raccoons using the latrines were eating corn and animal offal-based pet food provided by some residents in the area. Necropsies performed on 11 raccoons trapped on the property in connection with this investigation revealed that all (100%) were infected with B. procyonis. The patient’s behavioral history, large number of latrine sites, and the wide dispersal of raccoon feces observed on site indicated that the likelihood of exposure to infective B. procyonis eggs was extraordinarily high.

Can nutria be eradicated in Maryland?

The Presidential Executive Order 13112 for control of invasive species signed by President Clinton illustrates the national concern over the negative impact that nutria (Myocastor coypus) and other non-native, invasive species have on the nation’s natural resources. Nutria are established in 15 states nationwide and cause damage to agricultural crops and natural ecosystems. Despite efforts to control their populations, nutria are found in Maryland throughout the Eastern Shore and in the Potomac and Patuxent Rivers on the Western Shore. Twenty-three federal, state, and private organizations have combined their efforts to develop a three-year pilot plan for nutria control entitled "Marsh Restoration: Nutria Control in Maryland." In 1999 and 2000, funding became available to begin the first year of the three-year pilot effort. The objectives of the pilot program are to develop accurate population estimates, determine effective trapping strategies to maximize nutria harvest and minimize impacts to non-target species, evaluate the effects of population control on nutria home range and movement patterns, determine how population control affects nutria reproductive behavior, determine if the health of nutria populations is influenced by intense harvest pressure, and monitor the effects of intense nutria harvest on vegetative response. Implementation of the control plan will begin during summer 2000.

Successful eradication of introduced foxes from large Aleutian islands

The Aleutians are a volcanic chain of 200 named treeless islands, islets, and rocks that extend west off the Alaska mainland for more than 1,100 miles. Almost all of the Aleutian Islands have had non-native mammals introduced, including foxes, since their discovery by Russia in 1741. Most islands are in the Alaska Maritime National Wildlife Refuge, and since 1949, the U.S. Fish and Wildlife Service has eradicated foxes from 36 islands (951,174 acres) using various methods. Most recently, foxes have been eliminated from some of the largest islands (more than 50,000 acres) in the refuge by simultaneously trapping from three two-person camps using primarily leg hold traps. Recently, M44 devices were used during eradication efforts, although most foxes were taken by traps and shooting. Foxes are being removed to restore the native biological diversity.

The rat control program on the island of St. Helena

St. Helena is an Atlantic Ocean island lying 1,200 miles off the coast of Angola. Both species of commensal Rattus occur on the island, the ship rat (R. rattus) having possibly arrived as early as 1502, the year of the island’s discovery, and the brown rat (R. norvegicus) in the 1700s. Today, rats are widespread and common over the entire island, including the arid wastes, the inhabited and agricultural areas, and into the National Park around the central peaks. The impact of invasive rats on the endemic flora and fauna (predominantly invertebrate with many endemic species of snail, spider, and weevil being recorded) is unknown. The only natural enemies of rats on the island are occasional feral cats, raptors, and other predators being absent. In 1924, the Agriculture and Forestry Department started a 50 year poisoning campaign against rats which ended in 1956 when the brown rat was considered to be almost extinct. Since that time a continuous island-wide suppression campaign has been carried out by the Department of Public Health. This consists of placing anticoagulant baits in and around the inhabited areas of the island (and, on demand, in the agricultural and forested land) routinely, checking baits at least every two weeks and more often if take is high. On average, 20 tons of bait are laid every year. Data on baits placed, takes, and dead rats found were examined for the years 1995 to 1998. R. norvegicus was found to be the most common species, with the two species approaching 1:1 in only three areas of the island. A number of recommendations for the improvement of the rodent control program have been made with the overall aim of raising the professional status of the operators from that of "rat baiters" to that of professional pest control technicians. This will effectively raise the professional status of the Environmental Health Section as a whole. The aim is also to involve the public as partners for improvements in their own health and welfare.

Testing the dermal and oral toxicity of selected chemicals to brown treesnakes

Dermal and oral toxicity tests were conducted on brown treesnakes (Boiga irregularis) with active ingredients and insecticide formulated products registered with the U.S. Environmental Protection Agency (EPA). Over-the- counter drugs approved by the U.S. Food and Drug Administration (FDA) were evaluated for oral toxicity. Dermal applications of pyrethrin and pyrethroid commercially formulated aerosol insecticides containing the synergists piperonyl butoxide and n-octyl bicyloheptene dicarboximide were toxic to the snakes. The lowest oral gavage dose that resulted in 100% mortality for rotenone, pyrethrins, propoxur, and aspirin was 2.5, 40, 40, and 1,280 mg/kg, respectively; but, when these chemicals were consumed by snakes in bait matrices at doses several times higher than the gavage doses, mortality was greatly reduced. Uncoated tablets of aspirin (150 and 300 mg), ibuprofen (100 and 200 mg), acetaminophen (100 and 200 mg), and commercial over-the-counter tablet formulations of 80 mg and 325 mg acetaminophen were offered to snakes in a dead mouse bait matrix. The mortality with aspirin ranged from 67% to 100%. No mortality was observed with ibuprofen. Acetaminophen resulted in 100% mortality for each of the doses tested. Overall, these dermal and oral toxicity results indicate that some EPA-registered pesticides and drugs approved by FDA may have use as toxicants for brown treesnakes.

A history of muskrat problems in northeastern California

Northeastern California contains several extensive areas of natural and man-made wetland and marsh type habitats. These areas were void of muskrat (Ondatra zibethicus) until the early 1930s when deliberate introductions were made. Once a valuable renewable resource before the sharp decline in pelt prices and strict regulations on trapping, the muskrat has become a nuisance pest species for resource managers. Muskrats have caused extensive damage to water delivery systems, levees, dikes, stream and river banks. Other damage includes impacts on pasture, crops, livestock, property, fencing, fisheries, endangered species, and human health and safety. This paper will look at the types of damage caused by the muskrat and some of the management approaches being taken to reduce or alleviate this damage.

Management of exotic vertebrates: some of the New Zealand experience

Within New Zealand there have been more than 150 successful operations to eradicate exotic vertebrate pests from islands and many hundreds of operations to control exotic vertebrate pests on the mainland. This paper draws on this experience to discuss the justification and objectives for management of exotic vertebrate pests, selection of management methods and the measurement of success. The need to understand the biology of both the target species and potential non-target species is considered along with possible changes to inter-specific interactions following management of the target species. A variety of the tools that are available for management-from planning processes through traps to poisons and public consultation are discussed along with their impact on the environment, the target and non-target species. The need to measure, record and report results is emphasized.

Induced fertility as a wildlife management tool

A growing interest in nonlethal methods for population control of nuisance or damaging species of wildlife has fostered research in reducing fertility of these overabundant wildlife species. Fertility may be reduced by interfering with the fertilization of the egg (contraception) or interfering with the implantation or development of the fertilized egg (contragestion). Research using injectable porcine zona pellucida (PZP) and gonadotropin releasing hormone (GnRH) vaccines has demonstrated that several mammalian species can be contracepted, reducing fertility for several years without revaccination. However, because vaccines currently require delivery by syringe or bio-bullet, there is a need for infertility agents that can be delivered orally. Researchers are therefore considering materials that have resulted in reduced reproductive rates in the agricultural industry. Because of the cost of getting new technology approved by the FDA, materials already approved for other purposes that can be redirected for use in wildlife infertility may have a better chance of getting approved as wildlife infertility agents. Two compounds used in the broiler chicken industry have been found to reduce hatchability if given to the layer. Due to the rapid increase of Canada geese in our parks, research is ongoing with these two compounds to reduce hatchability in the Canada goose egg. Research is also underway to test a cholesterol mimic that competes with cholesterol as the parent compound for steroid synthesis. This compound could reduce fertility in both mammalian and avian species and is currently being tested in rodents. Natural plant materials such as phytoestrogens and ergot derivatives that result in reproductive losses in domestic animals should be also explored as reproductive inhibitors in overabundant species of wildlife.

Modeling the cost-effectiveness of wallaby control in New Zealand

Bennett’s wallaby (Macropus rufogriseus) was introduced to South Canterbury in New Zealand’s South Island in 1974. The species rapidly increased in numbers, and by the 1940s had increased to levels where it had become a significant agricultural pest. In 1947, a coordinated wallaby control program employing teams of shooters commenced. However, wallaby numbers stayed high, and it was not until the early 1960s when aerially sown 1080 baits were used that a significant reduction in wallaby numbers was achieved. However, the need to de-stock areas prior to application of the baits prompted fanners to demand control by shooting teams rather than poison in order to achieve ongoing control. Wallaby control in South Canterbury is managed under a Regional Pest Management Strategy, relying on shooting as the primary form of control, but using aerially distributed 1080 baits and 1080 gel applied to broadleaf foliage to a limited extent when and where necessary. Wallabies are continuing to expand their range into the central alpine region adjacent to South Canterbury where they are becoming a conservation threat on public lands. In this study, we re-analyzed 13 years of detailed hunting return data in order to derive a synoptic model of wallaby population growth relative to density and prevailing rainfall. We also estimated cost-effectiveness models for control employing shooting teams, aerially distributed 1080 baits, and 1080 gel applied to foliage. We then explored the cost-effectiveness of alternative strategies for wallaby control by combining the models predicting wallaby population growth with those predicting variation in the cost-effectiveness of available techniques. The implications of this study for ongoing wallaby control for mitigation of agricultural and conservation impacts are discussed.

Beyond citizen task forces: the future of community-based deer management

Public involvement in decision-making associated with wildlife management has progressed considerably over the past two decades. Wildlife managers became more inquisitive about both traditional and emerging stakeholders during the 1980s, a period when studies of key stakeholder groups became increasingly common. During the 1990s, public involvement in white-tailed deer (Odocoileus virginianus) management decisions shifted towards an emphasis on citizen task forces and similar transactional approaches, and a growing diversity of stakeholders contributed to making deer management decisions. This evolution continues, as communities are now sharing the cost and responsibility for deer management with state and local government agencies under a variety of co-management scenarios. We highlight a case study from Cayuga Heights, New York, where a community-based approach for setting management goals for an overabundant deer herd is currently being implemented. The community scale is appropriate because the impacts of deer are typically recognized by citizens at the local level, and the need for management becomes an issue in local communities. In addition, management actions can be perceived most readily by stakeholders at the community level. Experience is showing that outcomes of co-management at the community level are perceived as more appropriate, efficient, and equitable than traditional wildlife management approaches. Although co-management requires substantial time and effort, this strategy may result in greater stakeholder investment in and satisfaction with deer management.

Community based feral pig management in northern Australia's wet tropics

A community based approach to feral pig (Sus scrofa) management has been adopted in the Wet Tropics region of northern Queensland (Australia) to foster adoption of best practice principles and community ownership of the problem. The program has demonstrated trapping as a successful control technique in an environmentally sensitive area as well as key concepts desirable for community involvement in natural resource management. Approximately 700 traps are currently available for use by 41 community-based trappers, with more than 10,000 feral pig captures documented since 1993.

IPM strategies: Indexing difficult to monitor populations of pest species

Monitoring populations of problem species is an essential component for integrated damage reduction programs. Tracking population size through time and space helps define the potential magnitude and geographical extent of damage. Population size at an early stage of a crop cycle can serve as a predictor of damage levels later on, indicating whether control is necessary or what forms would be economically optimal. The ability to monitor for population change also permits assessment of the efficacy of the control methods for reducing numbers of a pest species. Methods for quantifying population levels can be as diverse as the number of subject species, the objectives of an IPM program, and whether direct estimates or indices of population parameters are required. Often, indirect methods involving counts of tracks, burrows, droppings, or food removal are used. We review methods used for a variety of wildlife species, examine the desirable characteristics for useful monitoring methods, and describe some of our current research on indexing methods.

Management of white-tailed deer in Chicago, Illinois forest preserves

The Forest Preserve District of DuPage County culled 2,826 white-tailed deer (Odocoileus virginianus), from 16 forest preserves in winters 1992-1998, including 1,786 from the 10 km2 Waterfall Glen Preserve. Methods of culling included sharpshooting or capture with a rocket-net followed by euthanasia via a penetrating captive bolt. Operational field costs were $119 to $310/deer. Population reconstructions indicated a decrease in deer population density at Waterfall Glen Preserve from 751 deer in 1992 to 55 deer in 1998. This reduction resulted in a significant decrease (r=0.9, P=0.001, n=7) in reported deer-vehicle collisions on adjacent roads from 30 in 1992 to 4 in 1998. Mean plant height, percent vegetative ground cover, and number of plant species increased (P< 0.0001) among years in six forest preserves experiencing deer population control. Culling was successful at reducing deer population density, decreasing deer-vehicle collisions, and assisting with the restoration of native ecosystems in DuPage County Forest Preserves.

Rating of killing traps against humane trapping standards using computer simulations

The Agreement on International Humane Trapping Standards (AIHTS) which applies to wildlife management, vertebrate pest control, and trapping for fur, skin, or meat for 19 listed species requires that a trapping method render at least 80% of a minimum of 12 target animals irreversibly insensible within a species-specific time limit. However, the Agreement also allows for the use of other scientifically proven methods as a substitute for testing on live animals. For the past five years, we have been developing computer models and simulation systems to determine whether killing traps meet humane trapping standards. The models were designed to classify the time-to-loss-of-sensibility of furbearing species based on mechanical characteristics of traps and strike location(s). Models were based on data collected from trap testing on marten (Martes americana), fisher (Martes pennanti), and raccoon (Procyon lotor). Models were tested against 15 years of live trap testing data from the Fur Institute of Canada. The models proved to be a valid alternative to trap testing on live animals due to their high levels of safe prediction accuracy (88%, 86% , and 92% for marten, fisher, and raccoon, respectively). If applied to trap testing, these models would dramatically reduce the cost and the need for trap testing on live animals.

Ecology and management of feral pigs in Australian tropical rainforests

Information on the ecological impacts of feral pigs (Sus scrofa) in the World Heritage Listed tropical rainforests of northern Queensland, Australia, are limited. This study quantifies and qualifies aspects of the ecological impact, spatial and temporal digging activities and home range and seasonal movement patterns of feral pigs. Feral pigs have seasonal digging activities with a preference for moist microhabitats at the start of the dry season. Feral pigs in this region have defined sedentary home ranges, and their distribution patterns appear to be influenced by microhabitat factors including earthworm populations and water availability. Digging activity decreases rainforest seedling survival rates by 36%. Management strategies should concentrate on a coordinated, regional, community based approach.

Biological control of vertebrate pests

Biological control of vertebrate pest species has evolved from classical "release and forget" strategies to current programs of integrated management, which in the future may include the use of genetically modified organisms. Key stages in the use of biocontrol are illustrated with the history of managing rabbits (Oryctolagus cuniculus) in Australia. Two pathogens have been successfully released, myxoma virus in the 1950s and rabbit haemorrhagic disease (RHD) virus in 1995, and both have been highly effective in suppressing rabbit populations. The rapid attenuation of myxoma virus, as well as bioclimatic constraints on its distribution, and the development of resistance in wild rabbits prompted the later release of insect vectors and highly virulent strains of the virus. The evolution of the current rabbit-myxomatosis-RHD-predator system is still being monitored, and research is in progress to add immunocontraceptive strains of myxoma virus to the suite of rabbit control techniques. Increased attention to measuring the outcomes of pest management resulted in a nationwide program to document the economic and environmental consequences of RHD. This program was conducted much more systematically than for introduction of myxoma virus or its vectors, and similar monitoring is likely to be mandatory for future biocontrol agents.

The effect of fertility control in the population dynamics and behavior of brushtail possums (Trichosurus vulpecula) in New Zealand

A large-scale field experiment began in late 1995 to determine the effectiveness of fertility control for managing brush tail possum populations in New Zealand. Six study populations received one of three sterility treatments, either 0%, 50%, or 80% of female possums sterilized by tubal ligation, with the level of sterility in each treatment maintained each year. Mark-recapture methods and analysis are being used to investigate the effect of the sterility treatments on demographic parameters such as population growth rate, survival, and recruitment. Recruitment of locally born young was successfully suppressed by sterility treatments, with lower yearling recruitment occurring on 80% and 50% sterility sites than on control sites. Negative population growth rate has been observed on one replicate set of 50% and 80% sterility sites, but growth rates have remained stable on the other replicate set of treatment sites. Examination of the contribution of immigrant animals to population growth rate has suggested that the settlement pattern of immigrants was compensating for reduced in situ recruitment. Analysis of survival rates revealed that sterile female possums had significantly higher survival rates than intact females, indicating a survival cost for reproduction. The effects of fertility control on the transmission rate of Leptospira interrogans serovar balcanica using a failure rate model revealed that the rate at which possums encounter Leptospira infection in the treatment sites (80% females sterile) was greater than the rate in control sites. As Leptospira infection is believed to be spread by direct contact, increased transmission in the 80% sterility sites suggests that contact rates between possums (mating contacts) are higher in areas subject to fertility control. Increased transmission is hypothesised to be driven by the increased frequency of oestrus resulting from the method of sterilization (tubal ligation) that was used to model the potential effects of immunocontraception. This result has direct relevance to both the epidemiology of disease as well as the potential spread of any biocontrol vector that relies on direct contact for transmission.

Implementation of regional pest management strategies

With the enactment of the Biosecurity Act 1993, New Zealand obtained enabling legislation which makes it possible to develop and implement regional pest management strategies (RPMSs) which are integrated in terms of multi species approach, funding, and outcome objectives. Up until this time local authorities, government departments, and landowners had mixed signals in terms of resource versus pest values, dated legislation, no long-term strategic approach to pest control, and certainly no guarantees for funding. The Waikato Regional Council (Environment Waikato) experience in developing and implementing a regional pest management strategy under the Biosecurity Act is studied and reported on for this paper.

Ecologically-based rodent management integrating new developments in biotechnology

Chemical control is currently the primary driver of "Integrated Pest Management" (IPM) for rodents. This generally provides effective control in the short term, regardless of the rodent species. However, governments are concerned about the use of chemicals, especially when they are striving to provide clean and green food products for their domestic and export markets. In developing countries, the challenge is first to develop a good understanding of the ecology of the pest species and then assess the efficacy of using traditional and new methods of rodent control. This will enable adoption of management actions that are more environmentally sound and sustainable (environmentally and culturally). This approach is termed "Ecologically-Based Rodent Management" (EBRM). How EBRM operates in an operational sense is presented for two rather different geographic regions, research approaches and strategies for management. The first research approach is ecologically-based management of rodent pests in rice fields of Southeast Asia. As an indication of their impact, rodents are the greatest agricultural problem in Indonesia causing annual losses to rice production of 17%. I report on the development of a rodent management project in West Java, Indonesia. The initial phase of the research was developing an understanding of the population ecology and habitat use of the main pest species, the rice-field rat (Rattus argentiventer). These findings have been combined with local knowledge (of rodents and farming systems) to develop an ecologically-based management strategy of the rice-field rat at a village-level. The second research approach is biological control of house mouse populations in Australia. Mouse populations erupt into plague proportions in cereal-growing regions causing substantial economic and social stress to rural communities. We are examining whether mouse populations can be managed with fertility control either by a non-infectious agent delivered in an oral bait, or by infectious viruses as carriers of an infertility agent. Although the focus is often on the biotechnology aspect of this research, it is knowledge of the population ecology of mice and the epidemiology of mouse cytomegalovirus in field populations that will provide the critical context for this management strategy.

Integrated pest management of black bear reforestation damage

Black bear damage to commercial, coniferous trees on intensively managed public and private forest lands of the Pacific Northwest continues to be a problem for forest managers. Historically, methods such as relocation or spring hunts have been used in an effort to reduce bear density and damage. More recently, supplemental feeding has been used in an attempt to provide for the nutritional needs of bears during the damage period. Alternative silvicultural practices and repellents are being investigated for their ability to reduce the likelihood of bear damage. These and other methods need to be examined for their effectiveness, especially in light of social attitudes, increasing costs, and legal constraints. As part of an integrated pest management (IPM) approach, there is a need to better define the nature, timing, and extent of tree damage by bears. We review the literature and discuss the results from several studies that help answer some of these questions. Managers and researchers will be continuously challenged to find innovative and publicly acceptable methods to maintain a harmonious and delicate balance between the needs and desires of humans and the needs and propensities of black bears.

Exposure of non-target wildlife to anticoagulant rodenticides in California

The California Department of Fish and Game collected and analyzed tissue samples from non-target birds and mammals for anticoagulant rodenticides from 1994 through 1999. Many of these animals were collected in recently urbanized areas adjacent to wildlands where they were either found dead or trapped and euthanized as vertebrate pests. The results of the analyses indicate a high frequency of exposure to the anticoagulant rodenticide brodifacoum. Fifty-eight percent of the animals examined had been exposed to brodifacoum, 19% to bromadiolone, 9% to diphacinone, and 8% to chlorophacinone. All of the identified anticoagulants are registered for use to control commensal rodents found in and around structures and are available for sale "over-the-counter" for homeowner use. Brodifacoum and bromadiolone are registered exclusively for commensal rodent control. This paper assesses the frequency of anticoagulant rodenticide residues in tissues of non-target mammalian and avian wildlife and the possible impacts.

Risk-benefit considerations in evaluating commensal anticoagulant rodenticide impacts to wildlife

Evaluation of the possible impacts of rodenticides on wildlife must be conducted in the context of risk-benefit considerations. Harmful introduced pests (e.g., commensal rats and mice) historically have required management around human habitation for economic and public health reasons. Disparate views of limited data have accumulated concerning the wildlife impacts resulting from commensal rodent control activities. The founding of the Rodenticide Registrants Task Force (RRTF), a trade association that includes all the major manufacturers and importers of anticoagulant rodenticide products (and bromethalin, a non-anticoagulant rodenticide) in the U.S., is described. The potential for anticoagulant dispersion in wildlife via primary and secondary routes is considered. Toxicology and pharmacokinetic studies are analyzed to obtain a better understanding of the biological and toxicological significance of low levels of rodenticide in animal tissue. A framework to address rodenticide impact to wildlife is presented. It is based upon the example of long-term cooperative efforts in England involving government, environmental, and manufacturer groups.

The rationale for requiring Bitrex and dyes in rodent baits

In 1998, the Environmental Protection Agency issued Reregistration Eligibility Decisions for the rodenticides Brodifacoum, Bromethalin, Bromadiolone, Chlorophacinone, Diphacinone, Pival, and Zinc Phosphide. These decisions imposed requirements that bait products containing these ingredients and marketed for control of commensal rodents also contain an "indicator dye" and a "bittering agent." The indicator dye would be used to mark children who come in contact with bait. The bittering agent would be used to render a bait unpalatable to children, possibly reducing the amount of bait eaten. This paper discusses these requirements and other regulatory attempts to limit risks of rodenticide baits to children and nontarget animals. EPA is reconsidering the requirements for the indicator dye and bittering agent. Currently, either type of agent may be added to a bait product voluntarily if the new bait can pass required efficacy tests.

Chlorophacinone and diphacinone: standard Mus musculus and Peromyscus maniculatus anticoagulant laboratory tests

The Vertebrate Pest Control Research Advisory Committee, through a cooperative agreement with the California Department of Food and Agriculture (CDFA), funded laboratory studies at the National Wildlife Research Center (NWRC). The objective of the studies was to obtain efficacy data for controlling house mice (Mus musculus) and deer mice (Peromyscus maniculatus) that would provide partial fulfillment of the requirements established by the Environmental Protection Agency (EPA) for the re-registration of the CDFA’s 0.01% chlorophacinone and 0.01% diphacinone grain bait labels. Swiss-Webster mice and deer mice from an on site breeding colony were placed on 15- day, two-choice feeding and efficacy trials. The control treatment groups received two dishes each containing the Office of Pesticide Programs (OPP) designated standard rat and mouse challenge diet. The treated groups received one dish of the standard OPP rat and mouse challenge diet and a second dish of the treated grain baits: 0.01% chlorophacinone (two groups of 20 animals, Groups II and III ), or 0.01% diphacinone (two groups of 20 animals, Groups II and III ) grain bait. Results from the treated groups of the four tests are reported. House mice on 0.01% chlorophacinone: female mortality was 100% in Group II and 90% in Group III. Total dietary consumption of treated bait was 23.0% of the total bait consumption. House mice on 0.01% diphacinone: female mortality was 90% in Group II and 100% in Group III. Total dietary consumption of treated bait was 18.2% of the total bait consumption. Deer mice on 0.01% chlorophacinone: female mortality in Groups II and III was 100%. Total dietary consumption of treated bait was 63.1% of the total bait consumption. Deer mice on 0.01% diphacinone: female mortality in Groups II and III was 100%. Total dietary consumption of treated bait was 66.3% of the total bait consumption. In conclusion, the female house mice ate less than the male house mice with the same mortality rate (between 90% and 100%); while the female Peromyscus ate more than the male Peromyscus, they had the same mortality rate (100%). The anticoagulant grain bait test mortality results for both house mice and deer mice met the suggested performance standard for the EPA Pesticide Assessment Guidelines.

U.S. EPA reregistration eligibility decision (RED) for the rodenticide cluster: overview of the regulatory process, response of registrants and stakeholders, and implications for agricultural and urban rodent control

After several years of reviewing study data and conducting risk assessments, in September of 1998 the U.S. Environmental Protection Agency (U.S. EPA) issued for comment a Reregistration Eligibility Decision (RED) document for pesticide products in the Rodenticide Cluster. The RED document covered 243 rodenticide products containing the following active ingredients: brodifacoum, bromadiolone, bromethalin, chlorophacinone, diphacinone and its sodium salt, and pival and its sodium salt. The U.S. EPA’s human health risk assessment in the RED document concluded that it was concerned about the risk to children due to accidental exposures to these chemicals through use in and around residences. With regard to ecological effects, the Agency concluded that there is a high risk of secondary poisoning, especially to mammals, from the use of these rodenticides outdoors in rural and suburban areas. In order to address the potential risks to children, the U.S. EPA initially required several mitigation measures designed to minimize exposure (e.g., addition of dye and bittering agent to formulations, labeling changes). The Agency also initiated implementation of a Rodenticide Stakeholder Process through which these and other risk mitigation measures would be discussed and required as needed. To help mitigate potential risks to non-target wildlife, the Agency initially determined that all uses of field-bait rodenticides containing more than 0.005% of chlorophacinone or diphacinone were ineligible for reregistration. The U.S. EPA also decided that all rodenticide products labeled for field use (except those limited to manual underground baiting) should be reclassified as Restricted Use pesticides. This paper reviews the regulatory process for the Rodenticide Cluster RED and discusses the response of the California Department of Food and Agriculture (CDFA) and other registrants to the requirements proposed in the RED document including formation of the Rodenticide Registrants Task Force (RRTF). It also outlines how an on-going dialogue with the Agency, both through the Rodenticide Stakeholder Process and in separate discussions, has diminished the RED requirements from those originally proposed. In addition, the paper discusses the implications and potential impacts of the current RED reregistration requirements for those applicators involved in agricultural and urban rodent control.

Wild dogs and their manipulation to prevent livestock predation in Australia

Dingoes and other wild dogs cause substantial damage and control expense in many Australian environments. The main methods of control are exclusion fencing, poisoning with 1080, and trapping. Strategies to mitigate livestock predation by wild dogs include; enterprise substitution, the reduction of wild dog populations, and baited buffer zones between wild dog country and sheep country. Damage functions show significant positive relationships between density indices and the losses caused by predation for both sheep and cattle enterprises. However, descriptive and explanatory models fitted the data poorly. A strategic approach to the management of wild dogs that aims to reduce predation on livestock while allowing the conservation of wild living dingoes is also outlined.

Measuring predator control effectiveness: reducing numbers may not reduce predator impact

The fundamental assumption in the management of predators is that reducing predator numbers will reduce their predation impact on livestock. Research on dingoes (Canis lupus dingo) has shown this assumption to be incorrect in beef production areas in northern and western Queensland. Aerial and ground baiting with 1080 (fluoroacetate) is the principal dingo-control method used in extensive pastoral areas of Australia. This paper compares four approaches to measure the effectiveness of these control programs. Dingo abundance was reduced in 11 of 13 baiting campaigns monitored with almost two-thirds of these producing >50% reduction. However, concurrent decline in dingo abundance occurred in non-baited areas due to seasonal changes in dingo populations. When this was taken into account, less than half of the control programs produced >50% reduction. The time taken for dingoes to recolonize baited areas is also an important measure of effectiveness. In two-thirds of the control programs, conducted in the first nine months of the year, dingoes recolonized prior to the period of peak calving (November/December) when the biggest threat to calves existed. The timing and the scale of control programs affect the rate of re-colonization. Calf loss was subsequently higher and occurred more frequently in baited areas compared to non-baited areas. Seasonal conditions, the status of prey populations, and the impact of control programs on social organization and prey selection, are key factors affecting calf predation. Control programs should be assessed by measuring impact rather than changes in predator numbers. The assumption that a direct relationship exists between predator numbers and impact is not valid for dingoes in beef production areas in northern Australia.

DNA identification of mountain lions involved in livestock predaton and public safety incidents and investigations

Using three case studies, we demonstrated the utility of techniques to analyze DNA from trace samples collected at sites of livestock predation and public safety incidents. Genetic analysis was used to determine species, individual identity, and relatedness between individuals. We documented the presence and individual identities of a mountain lion (Puma concolor) and a bobcat (Lynx rufus) from swab samples collected from bite wounds in domestic sheep that had been killed at the University of California Hopland Research and Extension Center, Mendocino County, California. Four lions and two bobcats in Redwood National Park were individually identified and tested for relatedness using DNA from scats and captured animals. Another lion was genetically typed and matched at a public safety incident through blood spots left near a barn in one location in the San Joaquin Valley, and muscle sample collected from a lion captured ten miles distant one week later. We applied statistical techniques developed for human forensic DNA analysis and a DNA database that we have compiled for California mountain lions.

Impact of free ranging dogs on wildlife in Italy

The diffuse presence of free ranging dogs (non-controlled, stray, and feral) in Italy is considered a severe conservation threat because of the potential impact on the wolf and on other wildlife species. In particular, it is generally believed that non-controlled owned dogs are rapidly increasing their number, representing a major part of the problem. The present legal framework does not allow destruction of dogs and cats, and the management of these pet species is based on mandatory marking, and on capture of free ranging animals for perpetual captivation in public kennels. The present research was aimed to: l) collect and analyze available information on the impact of free ranging dogs on the wolf and on wildlife; 2) census owned dogs in rural areas of Italy (including urban centers with less than 30,000 inhabitants); 3) estimate the proportion of owned dogs that are free to range; 4) assess the public perception of problems posed by free ranging dogs; 5) assess the public attitude toward management alternatives; and 6) define management guidelines. Free ranging dogs resulted to prey upon all ungulate species and colonial ground-nesting birds. Dogs are the main limiting factor in translocation projects involving roe and red-deer, and represent a key obstacle to the recolonization of central and southern Italy by these species. Impact on the wolf is also discussed. Dogs were censused through direct interviews to 2,903 Italian families, randomly selected by the electoral lists. The sample was homogeneously distributed in the country, in order to test for differences among areas (n=4 sub-regions: northeast, northwest, center, south and islands). The total number of dogs is estimated at 6,099,011 ± 307,234. Of these, 19.7% (n = 1,209,973 ± 151,280) are free to range at least part of their time. Despite the lack of reliable data on the past dog numbers, we estimated an average 5%/ year increase of the total population of dogs. The high increase rate is explained by the limited number of sterilized females, and the consequent high percentage of females reproducing every year. Number of dogs is negatively correlated to the size of urban areas, and increases from north to south. Control by owners follows opposite patterns. Despite the increasing number of non-controlled dogs, Italians have a limited perception of the social, sanitary, and conservation risks caused by dogs: 51.1% of Italians consider that dogs do not represent a problem at all, and only 3.8% of the population considers the destruction of dogs an acceptable alternative to perpetual captivity.

An experimental evaluation of lamb predaton in response to fox (Vulpes vulpes) control in south-eastern Australia

Fox predation has long been suspected as a major cause of lamb death in southern Australia. The response of farmers has been to poison foxes using sodium monofluoroacetate (compound 1080). This has become more widespread in recent years due to a number of factors including the reduced returns from sale of skins which has made shooting foxes unprofitable. In a replicated experiment we investigated the effect of fox control on lamb survival. Fox baiting was implemented at three levels; no baiting, baiting once a year before lambing (the recommended practice), and baiting three times a year. This was carried out on sheep properties with ultrasounded flocks over three years. The experiment was conducted in central New South Wales, Australia, in an area where wild dogs and native dingoes had been eradicated. Foxes, an introduced species, were the major mammalian predators of lambs in the district, as estimated from previous post-mortems of lamb carcasses. No significant difference was detected in lambing, as measured by the number of lambs per ewe at lamb marking 8 to 10 weeks after birth, however, there was a significant effect of fox control on the number of healthy lambs killed by foxes assessed by lamb post-mortems. The possible reasons for this result are discussed including features of the experimental design and the level of replication.

Development of chemical coyote attractants for wildlife management applications

Coyote attractants are inherently variable because they are usually derived by mixing and fermenting complex biologically derived substances. We designed the present study to address this problem. We collected volatiles by purge and trap headspace analyses from 33 commercially available attractants, and analyzed the trapped odors by gas chromatography with mass selective detection. We then statistically evaluated chromatographic peak area data to produce recipes for seven new chemical attractants. We presented these attractants to coyotes in one-choice tests at the Predation Ecology and Behavioral Applications Field Station of the USDA-APHIS-WS National Wildlife Research Center near Logan, Utah. Our results indicated that there were both seasonal and sexual differences in stimulus attractiveness. We also found that several attractants were more effective than Fatty Acid Scent (FAS), a commonly employed coyote attractant. A field trial to evaluate the effectiveness of new candidate attractants is planned.

The use of bone oil (renardine) as a coyote repellent on sheep farms in Ontario

As no control methods, apart from shooting and leghold traps, are legal in Southern Ontario, field trials of lithium chloride and bone oil ("Renardine") were carried out between 1991 and 1998. No effect could be demonstrated with lithium chloride. Between 1994 and 1998 bone oil was used as a repellent on seven different flocks, either directly onto the sheep or as a perimeter barrier round pastures. As long as the treatment was maintained, repulsion was achieved. The coyotes continued to kill in the surrounding area. If the odor level was not maintained, the coyotes would return to kill in the trial flocks. A slow release method for perimeter treatment was tried.

Evaluation of depredation management techniques for territorial animals using a computer model: coyotes as a case study

For centuries, coyotes have been controlled to protect livestock and/or enhance game populations. The intensity of control has varied widely and many types of control techniques have been used. The effects of these control techniques need to be evaluated to effectively resolve conflicts, to fulfill legal requirements, and to aid the development of new strategies. However, the influence of these techniques on coyote population size and structure is largely unknown. Furthermore, management decisions are often required before experimental tests can be developed, and conducting requisite experimental programs on meaningful scales are logistically prohibitive. Therefore, we developed an individual-based computer model to evaluate the effects of various control techniques on age structure including selective removal, random removal, and denning. This model is part of a larger effort to fully evaluate the effect of current management strategies on coyote populations and to eventually link this population model to a depredation model. Selective and random removal resulted in younger age structures, whereas denning produced population age structures similar to an unexploited population.

Evaluation of cabergoline as a reproductive inhibitor for coyotes (Canis latrans)

Cabergoline, a prolactin inhibitor, was evaluated on its potential use as a reproductive inhibitor for coyotes (Canis latrans). Groups consisting of six female coyotes were randomly assigned to three treatments and a control group. At 25 to 35 days after fertilization, coyotes were palpated to verify pregnancy status. If an animal was confirmed pregnant, it was dosed with 50 μg, 100 μg, or 250 μg of cabergoline, or a placebo for seven consecutive days on approximately day 40 days of gestation. Five animals dosed with 50 μg of cabergoline, three dosed with 100 μg, and three animals receiving placebo whelped; no animals treated with 250 μg whelped. No drop in serum progesterone or prolactin levels were observed for the 50 μg and 100 μg treated groups. However, progesterone levels declined below 2 ng/ml in animals treated with 250 μg. Prolactin and progesterone levels in the control group followed typical patterns observed in pregnant canines. This study suggests that cabergoline is a potential reproductive inhibitor in coyotes. Future studies should determine if the efficacy of cabergoline in terminating pregnancy in coyotes could be improved with higher doses and at earlier stages of gestation.

Sheep-predation behaviors of wild-caught, confined coyotes: some historical data

As part of efforts to develop The Livestock Protection Collar (U .S. EPA Reg. No. 56228-22), we videotaped sheep-predation events by 23 (15 male and 8 female) wild-caught, confined coyotes (Canis latrans) in a 31 × 41-m enclosure. Coyotes were paired individually with a sheep (Ovis aries) during 1-h daily trials. Nineteen (13male and 6 female) of the coyotes made 75 fatal attacks of 1 to 7 sheep each; 4 coyotes (2 male and 2 female) made no fatal attacks despite 19 to 39 daily pairings. Of coyotes that made fatal attacks, 13 (9 male and 4 female) always attacked at the neck of sheep; 5 (4 male and 1 female) always attacked by nipping at the legs/head/back of sheep; and 1 attacked at the legs/head/back of sheep during two initial events, but subsequently attacked at the neck of sheep. Greater time in captivity was not correlated with trials preceding a fatal attack (rho= +0.23). Among coyotes making ≥2 fatal attacks, subsequent predation events occurred after fewer intervening pairings with sheep. Initial feeding sites occurred most frequently at the flanks/ribs of sheep. Although collected between 1976 to 1980, these observations represent a never-to-be-acquired-again data set that remains timely. Data showed that not all coyotes display sheep-predation behaviors or kill sheep efficiently. Instrumental learning and stimulus-habituation models of coyote predation behavior are discussed.

Mechanisms of diet selection in coyotes (Canis latrans)

Coyote depredation is estimated to cause in excess of $11 million in damage annually to the national livestock industry. Numerous studies suggest coyotes forage optimally. Yet, not all coyotes kill prey with high nutritional benefit to cost ratios (e.g., livestock) when given the opportunity. This suggests that there are other means by which coyotes select prey items. Little research has been conducted to determine the mechanisms driving the selection of particular food items. Previous experience with certain tastes or flavors may play a part in the subsequent selection of prey items. Dietary preferences can be formed in young animals through exposure to chemical cues in utero, in milk, and at weaning. Studies on captive animals are useful in evaluating the importance of exposure to chemical cues on the formation of dietary preferences in adult coyotes. A review of relevant literature is given and management implications are discussed.

Response of captive coyotes to renardine coyote repellent

Renardine is a bone tar product available for use as a coyote (Canis latrans) repellent in Canada. The substance is applied to pasture borders to prevent coyotes from entering and attacking sheep. Because data regarding the effectiveness of Renardine are lacking, we designed two experiments. In the first, six pairs of coyotes were first presented with 400 g of ground meat in two pans (200 g/pan) with false screen bottoms. Beneath the screens were absorbent tubes wetted with 10 ml of distilled water. Subsequently, during a treatment period, the absorbent tube was wetted with 10 ml of Renardine. Pans were presented for 60 minutes, and the amount of time to consume the meat was recorded. In the second experiment, six additional pairs of coyotes were first presented with 200 g of ground meat inside a barrier created with baling twine and wooden dowels. The area inside the barrier was 1 m2, and the twine was tied onto the dowels 0.25 m above the ground. During the treatment period, the twine and dowels were painted with Renardine. In both experiments, all coyote pairs consumed all of the ground meat shortly after presentation. We conclude that Renardine probably is not an effective coyote repellent. However, because the active ingredient in Renardine is bone tar oil and bone tar oil is deer repellent, we speculate that Renardine may have utility as an herbivore repellent.

A comprehensive rodent control for Washington, D.C.

An effective rodent control program includes a team approach with centralized management and accountability. Environmental factors, the behavior of people, and the capability of organizations (government, businesses, and communities) must be evaluated when a rodent control program is designed. There must be excellent resources for community outreach, regulatory enforcement, and data management. Personnel must have technical skills and the ability to work with people. The program team should include several municipal organizations, each with defined responsibilities and communication structure. The pest control, landscaping, restaurant, and solid waste industries must be integrated into the program. Sustainability, cost-containment, and success ultimately are predicated on diverse community involvement.

Use of zinc phosphide for California ground squirrel control

Zinc phosphide (ZnP) is the only acute rodenticide currently registered for control of the California ground squirrel (Spermophilus beecheyi). Research has shown ZnP to give excellent control of sciurid rodents, but operational control programs in California have reported poor and inconsistent control. We examined the literature and conducted 34 field trials between 1996 and 1999 in order to identify factors affecting the field efficacy of ZnP. Important factors identified from the literature include bait acceptance, prebaiting, and timing of control operations in relation to ground squirrel and vegetation phenology. We used ground squirrel counts or active burrow counts to assess the efficacy of ZnP in the field trials. Treatments were either mechanical broadcast or spot baiting of 2% ZnP-treated oat groats. The first field trials in 1996 and 1997 were conducted without bait acceptance tests and prebaiting, and control was inconsistent, ranging from none on one plot, poor on three plots (45% to 63%), to good on two plots (84% to 87%). Field trials in 1998 and 1999 were conducted with bait acceptance tests and pre-baiting. In 1998 control was excellent (88% to 100%) on all plots. However, control was variable in 1999 trials with good control (80% to 90%) on five plots, but poor control (60% to 79%) on two plots, and no control on one plot. In our studies, pre-baiting had little effect on the efficacy of the ZnP for controlling California ground squirrels.

Pocket gopher (Orthogeomys hispidus hispidus) damage in sugarcane fields in the state of Veracruz, Mexico

Information concerning hispid pocket gopher (Orthogeomys hispidus hispidus) damage to sugarcane and the efficacy of sodium monofluroacetate (Compound 1080) treatments for control of this pest were obtained for the State of Veracruz, Mexico. Pocket gophers represent one of the major vertebrate pests based on the severity of economic losses caused to the sugarcane industry in this state. Pocket gophers cause significant damage in over 200,000 ha of sugarcane fields. In this study, a total of 66,560 stalks were examined for damage. Total percentage damaged was 20.67. Economic loss caused by pocket gopher was estimated at approximately $951 in one grower processor’s crop based on the 1998-99 price for raw sugar ($25 dollars/ton). Losses due to this pest species are probably underestimated because many sugarcane industries could not or did not provide loss estimates.

Reduced risk anticoagulant baiting strategies for California ground squirrels

The anticoagulants diphacinone and chlorophacinone (0.01% and 0.005% concentrations) are used extensively for control of California ground squirrels (Spermophilus beecheyi). Because of concerns of risks to nontarget wildlife, there is a need to develop baiting strategies that minimize the amount of bait applied, while still providing a high level of control. In 1997 and 1998, we conducted laboratory studies to determine the effect of timing and number of bait applications, and amount of bait given per application on the efficacy of 0.01% diphacinone for California ground squirrels. Results suggest that only two applications with 4 or 5 d between applications are necessary to achieve control. This is in contrast to the label recommendation of three to four applications with 48 h between applications (spot baiting), and two applications with 2 or 3 d between them (mechanical broadcast baiting). Furthermore, in our study, squirrels only required a small amount (less than 4 g of bait) per application to receive a lethal dose. Field studies are underway to test this baiting strategy and various bait application methods in the field.

Lesser-known vertebrate pests of almonds in California

During a three-year study to assess the effectiveness of broadcast distress calls on American crows (Corvus brachyrhynchos) in almond orchards, we had the opportunity to identify other vertebrate pests, some of which are not well documented. We describe the damage caused by these "lesser-known" species and in selected cases estimate the crop loss from these other pests in eight orchards in the Central Valley of California. In addition to crows and California ground squirrels (Spermophilus beecheyi), we recorded the presence of seven other vertebrate pests: scrub jays (Aphelocoma coerulescens), yellow-billed magpies (Pica nutalli), common ravens (Corvus corax), deer mice (Peromyscus spp.), western gray squirrels (Sciurus griseus), wild pigs (Sus scrofa), and beaver (Castor canadensis). Jays and magpies were found in six of eight orchards and caused damage of at least $56/ha at one site. Jays and magpies showed a preference for the soft-shelled Nonpariel variety of almond and tended to damage trees throughout the orchards, as opposed to concentrated damage along the edges. Ravens and wild pigs were found only in two Fresno County orchards located next to wildlands of the Coast Range Mountains. We could not specifically identify nor value damage by ravens as they may have reacted to the broadcast crow distress calls and abandoned the treated orchard. Nut loss from pigs amounted to $17/ha. Pig damage could be identified from tracks, broken branches, and the smashed appearance of damage nuts. Deer mice were the most serious pest in the two Fresno County orchards with damage of up to $51/ha. Signs of deer mouse damage included small, fine incisor marks around the edge of the hole in the nut, small shavings from the hull and shell, and a concentration of damaged nuts in the crotch of the tree and around the base of the trunk. Tree squirrels were the most serious pest in one orchard with damage of $46/ha. Tree squirrel damage was concentrated on particular trees in the orchard and damaged nuts were opened in a characteristic manner. Beavers felled almond trees at one orchard located next to a watercourse. We speculate the presence and abundance of a vertebrate pest relate to local habitat conditions, geographic location, the adaptability of species, and the dynamic nature of wildlife populations.

Fumigant dispersal in pocket gopher burrows and benefits of a blower system

Efforts to establish tree seedlings on sites infested with high populations of pocket gophers (Thomomys spp.) can be futile unless population control measures are implemented. Fumigants are a possible means to reduce pocket gopher populations although the efficacy of fumigants on reforestation sites has been minimal. We conducted a series of experiments to monitor the movement of carbon monoxide through burrow systems and to assess the potential benefits of a blower system. In the first experiment, carbon monoxide was introduced to an artificial burrow system by burning either one or two gas cartridges concurrently or consecutively. The blower was tried at different speeds for varied durations. Carbon monoxide concentration was monitored with sensors that had a detection range from 0 to 5,000 parts per million. Burning the cartridges without the blower was not effective in distributing carbon monoxide. The most effective fumigant dispersal occurred when the blower was used at a low speed for only the period while a cartridge was burning. Burning two cartridges simultaneously was the most effective burn configuration. Results from a second experiment, using vacated pocket gopher burrows instead of an artificial system, were similar to those recorded for the first experiment. Subsequently, we conducted field trials using a blower to disperse carbon monoxide to reduce pocket gopher populations on reforestation sites. These trials did not demonstrate a reduction in pocket gopher activity. We speculate this was because existing burrow plugs prevented the gas from dispersing through the systems or because pocket gophers rapidly blocked burrows when they detected the gas, thus preventing exposure to lethal gas concentrations.

Evaluation of the efficiency of three types of traps for capturing pocket gophers

Trapping is an integral tool in research and control of damage caused by pocket gophers (Thomomys spp.). We evaluated three types of traps (Macabee®, Cinch, Blackhole® Rodent) in a California field trial by comparing the number of captures to activity at the sets (capture efficiency) and separately, the duration of time from first to last capture (time efficiency). On each of six study plots established on irrigated agriculture fields, 60 trap stations were established at locations of gopher mounds. One trap type was used per station and traplines were run continuously for about four days. We captured a total of 256 gophers. Overall, the Cinch trap had the highest capture efficiency (41.7%), followed by the Macabee® trap (27.7%) and the Blackhole® trap (18.3%). The Cinch trap had a significantly greater (P=0.003) capture efficiency than either of the other two trap types, which did not differ (P>0.05). From a time efficiency standpoint, the Cinch trap also ranked first (0.046), the Macabee® trap second at 0.036 and the Blackhole® trap last (0.032), though the differences were not significant (P=0.693). We conclude that the Cinch trap was the most efficient of the three trap types for capturing gophers in this study. Its chief drawback is that the large baseplate makes it more time-consuming to set. The Blackhole® Rodent trap was the least efficient for capturing gophers, and very time-consuming to set and check. Furthermore, the floor of the trap (solid plastic) may have induced trap shyness, even when covered by soil. The Macabee® ranked intermediate in both capture efficiency and time efficiency. Due to its small size and ease to set and check, it will probably remain a popular alternative for capturing pocket gophers. An integrated pest management approach is recommended for the most effective control of pocket gophers.

Soil-moisture preferences and soil-use behaviors of Northern pocket gophers

Factors affecting soil-contact and -manipulation behaviors of pocket gophers (Thomomys and Geomys spp.) are poorly understood. Delineation of these behaviors is crucial to development of new repellent systems that seek to exploit the fossorial activity of these rodents. In a laboratory study involving northern pocket gophers (Thomomys talpoides), I examined the effects(s) of gravimetric soil moisture (i.e., 0%, 5%, 10%, 15%, 20%, and 25%) upon soil-contact and -use behaviors. Six gophers received successive, 0.5 h/day exposures to one of the moist soils compared to dry (0%) soil in a 2-choice apparatus. Times in each compartment and observed behaviors were recorded. A chamber × moisture interaction was attributed to the avoidance of 25% moist soil. A qualitative description of 37 locomotor, postural, sniffing, grooming, feeding, and soil-manipulation responses is provided.

Hand baiting efficacy of chlorophacinone and diphacinone grain baits to control Valley pocket gophers

Valley pocket gophers (Thomomys bottae) cause considerable damage each year to a variety of crops. In the fall of 1997, efficacy data were collected after the hand placement of anticoagulant grain baits into underground burrows of Valley pocket gophers in northern California. Twenty-four Treatment Units (TUs) were divided into one of four treatment groups: 1) 0.01% diphacinone; 2) 0.005% diphacinone; 3) 0.01% chlorophacinone; and 4) 0.005% chlorophacinone grain baits. Each treatment group contained five treated TUs and one control TU. Active burrow systems were hand baited with the respective baits. Efficacy was determined through use of the open-hole index and radio telemetry. Neither the 0.005% or 0.01% chlorophacinone or diphacinone grain baits met the Environmental Protection Agency’s 70% standard for verifying efficacy of rodenticides. Potential reasons for the low efficacy of less than 10% for the four treatment groups are discussed.

Impact of orchard vegetation management on small mammal population dynamics and species diversity

Voles of the genus Microtus feed on bark and vascular tissues of trees in fruit orchards across North America. Management of orchard floor vegetation with multiple applications of herbicide effectively altered habitat and reduced montane vole (M. montanus) populations in apple orchards near Summerland, British Columbia, Canada. Non-target populations of deer mice (Peromyscus maniculatus), northwestern chipmunks (Tamias amoenus), and Great Basin pocket mice (Perognathus parvus) appeared to respond positively to the treatment units. None of these non-target species was adversely affected by the actual herbicide treatments. Species diversity of small mammal communities in treated orchards was the same as that in untreated orchards and nearby old fields. Orchard agroecosystems with intensive vegetation management regimes appear to maintain diverse non-target small mammal communities.

The impact of the European rabbit (Oryctolagus cunniculus) on forest trees

The rabbit is the most important mammalian pest of forest trees in Ireland. Damage can occur at all times of the year but the most severe damage has been reported in the late winter/spring period. Damage includes browsing to the leaders and side shoots and bark stripping. Four tree species, penduculate oak (Quercus robur), Ash (Fraxinus exelisor), Sitka spruce (Picea sitchensis), and Japanese larch (Larix kaempferi), were identified as being particularly susceptible to all forms of damage. Beech (Larix sylvatica), sweet chestnut (Castanea saliva), and Douglas fir (Pseudotsuga menziesii) all displayed low levels of damage. The levels of damage to individual tree species varied with food availability. Trees planted in clear felled areas were severely damaged where there was a delay between harvesting and replanting. A delay of two years will allow the buildup of the rabbit population in the clear felled area. Avoidance of such damage will necessitate a census of the area before clear-felling, elimination of the rabbit population where feasible, or fencing out of rabbits before planting.

Overview of Wildlife Services' adverse incident reports FIFRA Section 6(a)(2)

The United States Department of Agriculture / Animal and Plant Health Inspection Service (APHIS) / Wildlife Services (WS) program fulfills a Federal responsibility for helping solve problems which occur when human activity and wildlife are in conflict with one another. This is accomplished through the recommendation and/or implementation of integrated pest management strategies (IPM). WS IPM strategies often involve both technical assistance and direct damage management. One management technique used by WS is the application of Federally and State registered vertebrate pesticides. APHIS has several vertebrate pesticides registered for use by WS. On June 16, 1998, the U.S. Environmental Protection Agency (EPA) passed a final rule amending the Federal Insecticide, Fungicide, and Rodenticide Act, Section 6(a)(2) on the reporting requirements for adverse incidents that involve pesticides. Adverse incidents, as defined by the EPA, can affect non-target wildlife, domestic animals, humans, property, and plants. WS employees reviewed the program’s pesticide records for potential adverse incidents dating back to January 1, 1994. In this paper, we discuss the minuscule impacts WS has had on the environment while using registered pesticides.

Charismatic megafauna or exotic pest? Interactions between popular perceptions of feral horses (Equus caballus) and their management and research

To date, management and research on feral horses have been strongly influenced by concerns and priorities of the general public. Due to outcry from numerous interest groups, research and management of feral horses have tended to be autecological, focused on individuals rather than populations, and addressing potential competition between horses and cattle, thus largely ignoring questions addressing roles that feral horses may play in arid and semiarid ecosystems. Management can never satisfy all desires of all interest groups, and research rarely can give answers so definitive that further questions will not arise. However, as we attempt to demonstrate, both management and research can help shape and inform public opinion through numerous means. Because feral horses have been one of the most contentious management issues of the last 100 years, it is critical that managers and investigators address both immediate and long-term concerns in their work. Honest communication of results and associated levels of uncertainty, along with rigorous testing of alternative explanations, are essential in issues having high levels of sociopolitical interest. Continued use of relevant, well-planned investigations in concert with thoughtful management may help define the future role the feral horse will play as "an integral part of the system of public lands" in the western United States.

How demographics, knowledge, and perceptions influence opinions of a 1994 Oregon hunting ballot initiative: Comparing voters and black bear hunters

We conducted phone surveys of bear hunters (n=714) and randomly-selected registered voters (n=327) to compare how demographics, knowledge of black bear (Ursus americanus) biology, and perceptions about black bear populations in Oregon differed between the two groups and how these differences influenced personal opinions of a 1994 ballot initiative that banned two bear hunting techniques (Measure 18). Responses differed between voters and hunters for almost all questions. In contrast to respondents who disagreed with Measure 18, both hunters and voters who agreed with Measure 18 were less likely to belong to a hunting organization and tended to believe that black bear populations were increasing and that bears were dangerous or potentially dangerous. In addition, voters who were female and who obtained information primarily from television and newspapers were more likely to agree with Measure 18. Surveys of public knowledge, perceptions, and opinions can help wildlife managers identify issues, design ongoing public information campaigns, predict outcomes of ballot initiatives, and predict support for proposed management policy and regulation changes.

The grey squirrel in Italy: risks of expansion and related threats to the survival of the red squirrel in Europe

The American grey squirrel, imported to Italy in 1948, represents a threat to the indigenous red squirrel, and an eradication of the alien species has been asked by several national and international organizations. In 1997, the National Wildlife Institute started an experimental eradication in the Racconigi Park (northwest Italy), aimed to evaluate the reliability and efficiency of humane removal techniques, through live-trapping, anaesthesia, and subsequent euthanasia of squirrels. The program, supported by most NGOs, was strongly opposed by radical animal right groups, who took the author and the director of the National Wildlife Institute to court, causing a halt of any activity. The species has expanded since then, and an eradication is no longer considered feasible. A colonization of the entire Alps in the middle term and of a large part of Europe in the long term is predicted, potentially threatening the survival of the red squirrel in the continent.

The relationship of animal protection interests to animal damage management: Historic paths, contemporary concerns and the uncertain future

More than a decade ago Schmidt (1989) called for consideration of animal welfare to become a "first-order" decision rule in wildlife management concerns, including animal damage control. Although there has been movement in that direction, this clearly has not yet come to pass. This paper takes a brief look at the interests we call animal damage management, animal welfare and protection, animal rights, and environmentalism in order to speculate about their shared concerns and the uncertain future before them. Since animal damage and the management of that damage cannot be abstracted from the environmental context in which they occur, this leads to speculation that some confluence of the interests of animal damage management, animal protection, and environmentalism will lead to a new disciplinary focus in the future.

Cage trap modifications that enhance the capture success of raccoons

Raccoons (Procyon lotor) often are considered a nuisance species in suburban and urban areas, and thus, must be removed. However, raccoons are capable of removing bait from cage traps without being captured and appear to avoid baits that are infested with fire ants (Solenopsis invicta). We modified Tomahawk® cage traps with an extended metal floor that acted as a trip device, hardware cloth wrapped around the back half of traps to reduce the potential of raccoons obtaining bait without entering the traps, and developed a hook upon which to place baits to minimize the probability of fire ants locating the bait. We then compared the proportion of raccoon captures, baits missing, and baits with fire ants between cage traps with and without the modified floor and bait hook. Twenty-five raccoons were caught, 80 baits were stolen, and 108 baits were infested with fire ants during 432 trap-nights. A greater proportion of raccoons were caught in (G=11.7, 3 df, P<0.01) and fewer baits were stolen from (G=11.0, 3 df, P<0.02) cage traps modified with the extended metal floor than without the modification. Traps equipped with hooks were minimally affected by fire ants present on the baits (i.e., 8 of 216 baits; 3.7%), which was much less (G=59.0, 1 df, P<0.0001) than traps without bait hooks (46.3%). Our modifications to cage traps enhanced the capture success of raccoons and should be considered if live-trapping of raccoons is required, especially in areas where fire ants are problematic.

Urban-suburban prairie dog management: opportunities and challenges

The historic range of the black-tailed prairie dog has undergone dramatic declines in the last century, prompting concern about the species’ long-term viability. While considered a pest by many, others believe that the species is a "keystone" element of prairie ecosystems. Urban-suburban land managers are challenged with preserving colonies of prairie dogs on public lands while dealing with many conflicting interests, social costs, and risks. We review the management plans that municipalities have designed to reduce conflicts by using public input, zoned management, and a variety of management techniques. Areas of difficulty and research needs are also discussed.