Proceedings of the Vertebrate Pest Conference

Small Indian mongooses are detrimental introduced predators in the United States, where they depredate native species, serve as vector of disease, and threaten public safety. Due to the risk of accidental introduction to mongoose-free islands, high cost and limitations to trapping, and no national (Section 3) Environmental Protection Agency (EPA)-registered toxicants for mongoose control, there is a need for an efficacious toxic bait for mongooses for use in conservation areas and at points of entry in the United States. Over the last five years, the National Wildlife Research Center (NWRC) worked to develop a toxic bait for mongooses for registration with the EPA. This paper outlines the development pathway to registration of a toxic bait for mongooses in the United States.

The management of free-roaming horses (Equus ferus) and burros (E. asinus) in the United States has been referred to as a “wicked problem” because, although there are population control options, societal values will ultimately determine what is acceptable and what is not. In the United States, free-roaming equids are managed by different types of organizations and agencies, and the landscapes that these animals inhabit vary widely in terms of access, size, topography, climate, natural resources, flora, and fauna. This landscape diversity, coupled with contemporary socioeconomic and political environments, means that adaptive management practices are needed to regulate these free-roaming populations. The Bureau of Land Management (BLM) currently manages free-roaming equids on 177 herd management areas in the United States by applying fertility control measures in situ and/or removing horses, which are either adopted by private individuals or sent to long-term holding facilities. The BLM off-range population currently includes >50,000 animals and costs approximately $50 million USD per year to maintain; on-range equid numbers were estimated in March 2022 to be approximately 82,384. On-range populations can grow at 15-20% annually, and current estimates far exceed the designated appropriate management level of 26,715. To reduce population recruitment, managers need better information about effective, long-lasting, or permanent fertility control measures. Because mares breed only once a year, fertility control studies take years to complete. Some contraceptive approaches have been studied for decades, and results from various trials can collectively inform future research directions and actions. Employing one or more fertility control tools in concert with removals offers the best potential for success. Active, iterative, cooperative, and thoughtful management practices can protect free-roaming horses while simultaneously protecting the habitat. Herein, we review contraceptive vaccines, intrauterine devices, and surgical sterilization options for controlling fertility of free-roaming horses. This review provides managers with a “fertility control toolbox” and guides future research.

Landscape affordances, what the environment offers an animal, are inherently species-specific to the extent that each taxon has unique needs and responses to landscape characteristics. Wildlife responses to landscape features range on a continuum from avoidance to attraction, and quantifying these habits are the backbone of wildlife movement ecology. In anthropogenically modified landscapes, many taxa do not occupy areas heavily influenced by humans, while some species seem to flourish, such as coyotes (Canis latrans) and pigeons (Columba livia). Sufficient overlap in landscapes designed for human purposes (e.g., freeway underpasses, channelized waterways, and cemeteries) but which are also suitable for wildlife (e.g., by providing sources of food, shelter, and refuge) underlies wildlife persistence in urban areas and is increasingly important in the world’s largest metropoles. Studying these overlapping worlds of humans and wildlife in cities provides a rich foundation for broadening human perceptions of cities as ecosystems that exhibit emergent hybridity, whereby certain anthropogenic features of urban landscapes can be used by wildlife even as they maintain their utility for humans. By examining scaling dynamics of the infrastructural signature, the phenomena of urban wildlife movement patterns conforming to the shapes of human infrastructural forms, we hope to expand on prior research in wildlife landscape ecology by stressing the importance of understanding the overlapping worlds of humans and wildlife. Further knowledge of the urban ecological commons is necessary to better design cities where emergent hybridity is leveraged toward the management goals of reducing human wildlife conflict and promoting biodiversity.

Secondary exposure to anticoagulant rodenticides (ARs) remains a significant problem for wild carnivores living at the urban-wildland interface. Although direct mortality is the most obvious concern, AR exposure may also cause subtle, sub-lethal effects, such as reduced body condition and increased parasite loads, that ultimately contribute to poorer performance at the population level. However, relatively little is known about such effects on wild animals, or about the environmental factors that contribute to AR exposure. We examined relationships between levels of AR exposure, demographic factors, and landscape variables associated with urbanization, for coyotes (Canis latrans) from urban Los Angeles and Orange counties, California. AR exposure was estimated from residue assays of livers from 353 carcasses, collected opportunistically as road kills or euthanized nuisance animals from 2015 to 2018. We also conducted veterinary necropsies on a subset of 50 carcasses to investigate effects of AR exposure on body weight, overall condition, and parasite burdens. Nearly all coyotes (98%) contained residues of at least one AR, with second-generation ARs (SGARs) detected in 97%, first-generation ARs (FGARs) detected in 75%, and 66% exposed to both types. Individual coyotes had residues of 0-6 compounds (mode = 4), with three SGARs (bromadiolone, brodifacuom, difethialone) and one FGAR (diphacinone) detected often (≥65 coyotes). Adults were exposed to more ARs and had significantly higher residue concentrations than juveniles. Road-killed coyotes were over-represented among coyotes with high numbers of SGARs and had significantly higher SGAR residue levels than euthanized ones. Contrary to our expectations, landscape patterns suggested higher numbers and residue concentrations of SGARs in coyotes associated with less intensive urban development. Very few coyotes (6 of 353) showed any evidence of mange, and these animals had similar AR numbers and residue concentrations to those without mange. Of the 50 animals that we necropsied thoroughly, coyotes with obvious internal hemorrhage tended to have high residue concentrations of SGARs, while those exposed to multiple FGAR compounds and with high FGAR residue concentrations tended to be in poorer body condition. ARs are an important tool for managing rodent pests but given the ubiquitous exposure of coyotes to ARs and evidence of potential sub-lethal effects, notably from FGARs, we need more information on pathways of exposure and better strategies to reduce the total amount of ARs on the landscape.

American black bears (Ursus americanus) can be considered vertebrate pests when they come in conflict with humans and create potential public safety situations that require intervention by local wildlife or animal control departments. Black bears are both omnivorous and highly intelligent, and this combination of characteristics make these animals prone to human habituation and developing an association between humans and easy sources of food. Foraging behaviors can put black bears in undesired or unsafe contact with humans when bears root through garbage on private and public lands, consume crops, prey upon small livestock or pets, cause significant property damage, and wander onto roadways leading to traffic accidents. An increasingly recognized cause of bear-human conflict is neurologic disease, such as that caused by infectious pathogens or toxicity, leading to cognitive or behavioral changes. A unique neurologic disease affecting black bears was first observed in 2014 near Lake Tahoe on the border between California and Nevada. Since then, it has been reported in eight counties in California and two counties in Nevada. Affected bears exhibit a range of neurologic symptoms including tremors, seizures, head tilts, and loss of fear of humans (i.e., “dog-like” behavior). Affected animals are typically young (<3 years old), underweight, and most often present in the spring after early emergence from hibernation. Histopathologic examination of brain tissue from these bears revealed varying degrees of inflammation in the brain (encephalitis), but the cause of this encephalitis was not apparent. Testing for common infectious causes of encephalitis (e.g., rabies, canine distemper virus, canine adenovirus, West Nile virus) and common neurotoxins did not identify a cause of the inflammation. A novel gammaherpesvirus, circovirus, parvovirus, and anellovirus were isolated from subsets of affected bears; however, a direct correlation between viral infection and encephalitis has not been established to date. The goal of this study is to investigate the potential role of protozoal parasites in this encephalitis of unknown origin, as members of this group of pathogens are known causes of encephalitis in humans and animals. Brain tissue from bears with encephalitis (n = 21) and unaffected bears (n = 15) from California and Nevada was screened via PCR targeting two loci commonly used to identify protozoal parasites (ITS1 and 18S). Protozoal parasite DNA was detected in 47.6% of bears with encephalitis (10/21) and 26.7% of unaffected bears (4/15). Parasites detected in bears with encephalitis included Sarcocystis neurona (4/21), S. canis (1/21), S. felis (1/21), an uncharacterized Sarcocystis sp. (1/21), Toxoplasma gondii (1/21), and an uncharacterized Cystoisospora-like species (2/21). Sarcocystis neurona, S. canis, and T. gondii are known to cause encephalitis in humans and animals. Sarcocystis canis is an increasingly recognized pathogen of bears and has been reported to cause inflammation in the brain, liver, and muscle in other geographical regions. The clinical significance of the poorly characterized protozoal species is uncertain. Parasites detected in unaffected bears included T. gondii (1/15), an uncharacterized Sarcocystis species (1/15) and an uncharacterized Cystoisospora-like species (2/15). These results suggest that protozoal parasites, particularly Sarcocystis species, may contribute to encephalitis in juvenile black bears, creating a public safety hazard at the human-wildlife interface.

California ground squirrels (Otospermophilus spp.) cause more economic damage to California rangelands than any other rodent (Baldwin et al. 2022). Burrow systems can undermine stock pond dams, ranch roads, and even hillslopes. However, forage loss is generally the primary concern. When asked, ranchers offer detailed qualitative descriptions of the damage ground squirrels cause and how it impacts the economic viability of their operations. Damage by ground squirrels can be particularly concerning because ranching operations are often on the margins of profitability. Unfortunately, few studies have quantified economic losses from ground squirrels. Additionally, ranchers commonly lease grazing land from public agencies. In many cases, agency employees have a limited understanding of ranching operations and generally do not allow for control of ground squirrels. Quantitative data on ground squirrel impacts to rangelands and ranching operations may help land management agencies better understand the challenges faced by their lessees and justify targeted management actions in the future. Therefore, we tested the amount of standing crop removed by ground squirrels across 16 sites on the Central Coast and interior central California 2019 and 2020. Sampling was conducted during a 4 to 6-week period in May and early-June. This timeframe coincided with the period after juvenile squirrels emerged from natal dens, which allowed us to quantify the collective impact that the entire ground squirrel population had on the landscape. We included four different ground squirrel density categories per site: minimal (0-1 squirrel), low (2-6 squirrels), medium (7-15 squirrels), and high (more than 15 squirrels). To quantify ground squirrels, we counted individuals in 0.4-ha plots using binoculars from an observation point outside the plots. We conducted five ground squirrel counts, repeated twice a day over three days for a total of 30 counts per plot, and used the highest number observed in analyses. We estimated standing crop (biomass of herbaceous vegetation) using the comparative yield method. We also evaluated precipitation and livestock grazing intensity in relation to forage production. We found that each ground squirrel reduced standing crop by 27.2 kg per ha. Precipitation also influenced forage production: each cm of precipitation yielded 16.6 kg per ha of additional available forage. In our model, identified effects of livestock grazing intensity; interaction between livestock grazing intensity and ground squirrel abundance; and interaction between precipitation and ground squirrel abundance on residual standing crop were not statistically significant. Although grazing intensity does influence vegetation biomass, we did not identify a significant relationship between the two, likely because we were limited to collecting grazing intensity data at the scale of the field, not at the scale of our survey plots. Despite their economic impacts, ground squirrels are critically important to California rangeland ecosystems. Ground squirrel burrows are documented to provide habitat for native wildlife including burrowing owls (Athene cunicularia) and California tiger salamanders (Ambystoma californiense). Ground squirrel colonies are also known to be associated with increased native bird species richness, diversity, and abundance (Lenihan 2007). Because of these potential benefits to supporting native wildlife, active ground squirrel management should only be conducted on rangelands when ground squirrel damage exceeds levels considered tolerable by ranch managers. The level of damage considered intolerable will likely vary among managers of different sites. Results from this study could help ranchers and other land managers identify when such a threshold is exceeded

Roof rats (Rattus rattus) are common invasive pests in both urban and agricultural sites as well as a significant public health threat. The use of anticoagulant rodenticides to help control the rodent population poses a risk of developing resistance to these products. Several reports have associated the non-synonymous Single Nucleotide Polymorphism (nsSNP) Tyr25Phe (Y25F) of the vitamin K epoxide reductase subcomponent 1 (Vkorc1) gene to anticoagulant rodenticide resistance (Diaz et al. 2021). We conducted a nsSNP screen in the population of Rattus spp. in Orange County to determine the prevalence of the Y25F nsSNP in the sampled rodents. Thirty-seven live rat traps were set throughout the county and the species of each trapped rat was determined by sequencing the cytochrome oxide I (COI) gene using primers previously described in Goulois et al. (2015). Twenty specimens were identified as R. rattus and 12 as R. tanezumi (Asian house rat); the other five specimens were non-Rattus species. To further evaluate the rat species, we used tree-based methods using sequence alignments for three mitochondrial DNA regions, cytochrome b, COI, and non-coding displacement (D) loop using a different set of primers used by Robins et al. (2007). Sequences were aligned by Geneious Prime (v.2020.2.4), and maximum-likelihood phylogeny using 1,000 bootstrap replications was constructed using Mega (10.2.6). Sequences were compared to reference sequences in Robins et al. (2007) and Rattus norvegicus (Norway rat) was used to root the tree. Phylogenetic analysis confirmed the presence of R. tanezumi in our collected samples as well as two haplotypes of R. rattus. In addition to the concatenated data set, each gene was examined individually, and all phylogenetic trees generally agreed on topology. The Y25F nsSNP was present in both R. rattus (40%; 8 of 20) and R. tanezumi (16.67%; 2 of 12). Further genetic testing in Orange County and other areas of Southern California are needed to determine the extent of these Rattus populations and their hybridization as well as the presence of this adaptive trait.

In 1983, Savarie and colleagues did an extensive study of the toxicity of para-aminopropiophenone (PAPP) in multiple species of mammals and birds (Savarie et al. 1983). They tested 15 species and found that PAPP was toxic to coyotes: the LD50 for coyotes via oral gavage in cod liver oil was 5.6 mg/kg. However, they also found that coyotes (and numerous other species) vomited after consuming PAPP and this vomiting likely decreased the efficacy of PAPP. They concluded that the induction of vomiting by PAPP must be addressed before it could be effective as a chemical to control coyotes (Savarie et al. 1983). Huo Ping Pan further investigated the effects of PAPP to coyotes in studies compiled in an internal report [Pan, unpublished report, National Wildlife Research Center (NWRC)]. In the study of Savarie et al. (1983), coyotes that consumed 150 mg PAPP in beef tallow baits vomited and recovered. Pan hypothesized that if the dose of PAPP was increased slightly, coyotes may succumb to PAPP without vomiting. He dosed coyotes with 200, 300, or 400 mg PAPP; all the coyotes except two at the 200 mg dose succumbed to the effects of PAPP. These two animals both lapsed into unconsciousness but had to be euthanized. One of these two animals and one animal at the 300 mg dose “slightly” vomited. Pan went on to test a dose of 350 mg more thoroughly. Nine of ten coyotes died within 2.5 hours of dosing and one survived. None of the ten coyotes dosed with 350 mg of PAPP vomited (Pan, unpublished report, NWRC). By increasing the dose of PAPP, Pan was able to overcome the problem of emesis that Savarie et al. (1983) reported. With the data generated from these studies, Pan and colleagues concluded that work with PAPP should continue, as they thought that it could be developed as a “superior substitute for 1080 as coyote control toxicant.” PAPP has been registered in New Zealand for the control of stoats and feral cats and in Australia for the control of wild dogs and foxes. The USDA APHIS Wildlife Services National Wildlife Research Center (NWRC) has an interest in the development of PAPP for coyote control. NWRC investigated the efficacy of PAPP as a means of lethal control in coyotes using multiple routes of administration. In initial studies, animals were orally gavaged with PAPP in an inert carrier to determine LD50 values and test LD100 doses. When used on the landscape a toxicant must be efficacious under varied conditions such as full or empty stomach. Therefore, after the initial trials, studies were done to determine the efficacy of PAPP in coyotes when the animals consumed PAPP with other food. Coyotes were also offered PAPP in meatballs and allowed to freely consume the food bait. In further trials, NWRC researchers tested the effectiveness of two different doses of PAPP capsules (880 mg and 400 mg) placed in a spring-loaded ejector device (SLED) to lethally control coyotes. Both doses were lethal to all coyotes tested, supporting further research into the development of PAPP as a tool to control coyotes.

Due to the economically and environmentally beneficial rodent control services birds of prey (raptors) provide, many property owners in North America and around the world install artificial nest boxes to attract breeding populations of barn owls as part of an integrated pest management (IPM) strategy. However, anticoagulant rodenticides (ARs) and barn owl biocontrol are often concurrently used to limit damage from rodent pest species in agricultural ecosystems which could lead to secondary poisoning of these beneficial predators. Substantial global effort is currently underway to determine the efficacy and cost effectiveness of this IPM approach, while better defining the risk to barn owls from potential AR exposure. While these issues have received increased attention, there is little data describing the circumstances in which barn owls interact with AR compounds, as well as the potential sublethal effects of AR exposure in these settings that may hinder a barn owl’s ability to adequately control pests in agroecosystems. By incorporating research techniques that can relate AR application to barn owl diet, movement, development, and secondary AR exposure frequencies, we can begin to understand the nature of employing chemical and biological control together in an IPM program. To understand the interactions between ARs and barn owls in IPM, we propose that studies investigate the frequency and severity of secondary poisoning in barn owls that are providing biological control on farms.

Roof rats cause extensive damage in orchards throughout the world. Integrated Pest Management (IPM) systems are the best option for managing rodents, yet few management systems have been developed and tested to control roof rats in agricultural settings. We initiated a study in 2020 to provide the foundation for an IPM program to manage roof rats in California citrus orchards. Our initial efforts centered on developing effective monitoring strategies for roof rats to determine when management actions are needed, assessing rat movement patterns to determine proper placement of management tools, and conducting initial tests of Goodnature A24 self-resetting traps and elevated bait stations containing 0.005% diphacinone-treated oats. We determined that the use of both tracking tunnels and remote-triggered cameras served as effective monitoring tools for roof rats in citrus orchards, and a smaller 3 × 3 grid placement of these monitoring tools was as effective as a 5 × 5 grid, indicating that substantial material and labor costs could be saved by using the smaller grid size. Placement of the monitoring tools on the ground or up in trees did not influence the effectiveness of this approach. We determined that roof rats exclusively used orchard habitats rather than surrounding fields, so control efforts should be focused in these areas. Roof rats moved substantial distances daily (~170-190 m), but results from bait station trials suggest that spacing of bait stations and traps should be closer together to increase roof rat encounter rates of these devices. Our trial with A24 traps elevated in orchard canopies suggest that there is an advantage to including a platform underneath the trap to increase trap activation. Collectively, this information provides a baseline for future research targeted at developing an effective IPM program for managing roof rats in citrus orchards.

In Modoc County, located in northeastern California, there is a high elevation sage-steppe rangeland ecosystem heavily populated by free roaming equids and managed primarily by the United States Forest Service (USFS) known as the Devil's Garden. Free roaming equid populations have significantly exceeded (roughly 2000 horses) appropriate management levels (206-402 horses) in the last decade and expanded their range outside of the designated territory (about 250,000 acres) and on to private and tribal lands (over 450,000 acres), degrading rangeland and threatening endangered species. Helicopter gathers in recent years have removed over 2000 equids from the Devil’s Garden. Due to an extensive collaboration between the USFS-Modoc National Forest, and local partners, many of these equids have found new homes. An early collaborative group developed unique strategies for placement of old (over nine years of age and historically characterized as unadoptable) and young horses. Modoc County has utilized the government- to- government communication process to participate in management decisions and worked to change federal law to provide USFS equal opportunity to placement programs. A robust social media campaign ran by local volunteers has created a brand for the Devil’s Garden equids and educated the public on the declining range condition and equid health. Volunteers also matched potential adopters and buyers with transportation options for cross country transportation and some funding for transportation of large groups of equids was provided. Finally, the Devil’s Garden Colt Challenge has placed nearly 100 horses with California 4-H and FFA youth over the last three years and additional horses with friends and family members.

Nutria (Myocastor coypus) are semi-aquatic rodents native to South America that were introduced into many countries outside their native range for fur-farming. Nutria are considered a pest species in many regions primarily because of their feeding and burrowing activities that damage water control structures, agricultural crops, and marsh vegetation, but they are also capable of supporting parasites and pathogens that could present health risks to humans and other animals (Howerth et al. 1994, Michel et al. 2001). Nutria populations in the United States are found in the Gulf of Mexico coast, the Atlantic coast, and the Pacific Northwest, where they are managed as invasive species or euthanized through local eradication efforts. Nutria in California were reportedly eradicated after a small-scale effort in the 1970s, but recently reappeared in the Central Valley in 2017. Nutria in California inhabit rivers, streams, lakes, and ponds where they exist alongside native aquatic mammals such as American beaver (Castor canadensis), common muskrat (Odontra zibethicus), and the North American river otter (Lontra canadensis). The re-emergence of nutria in the California Central Valley, nearly 50 years post eradication, necessitates further investigation into the impacts of this species. In this study, we investigated whether nutria in California serve as hosts for infectious agents that present spillover risk to susceptible host populations including native wildlife, domestic animals, and humans. We used histopathology, PCR, immunoassays, and morphologic identification of ectoparasites to evaluate the presence of pathogens or arthropod vectors in a subset of sixty-five nutria dispatched as part of a statewide eradication effort. Most nutria with lung tissue submitted for histopathology in this survey had evidence of interstitial pneumonia. The etiology was undetermined based on microscopic evaluation, and few were severe enough to have clinical significance. Further study to identify the etiology in these cases and better understand the implications of pneumonia in nutria may include culture, PCR, or metagenomic techniques. Some nutria had histopathologic evidence of hepatitis with intralesional cestodes. Molecular identification is needed to identify the species in these cases, although they morphologically resembled Taenia sp. Other infrequent findings included myocarditis, nephrosis, renal fibrosis, and dermatitis and orthokeratotic hyperkeratosis with pediculosis. PCR amplification and DNA sequencing of a region of the small subunit ribosomal RNA gene positively identified Giardia intestinalis from one nutria fecal sample. The sequence was aligned to previously described 18S rRNA sequences from the NCBI GenBank database for each assemblage (A-G), and was determined to be most closely related to assemblage B. Assemblages A and B are found in humans and are reported to be zoonotic (Thompson 2004). Further testing is warranted to determine the role of nutria in California as potential reservoirs for zoonotic G. intestinalis transmission. Three nutria were seropositive for L. interrogans, serovars Canicola and Pomona. We did not detect pathogenic Leptospira spp. by RT-PCR. Leptospirosis is common in California wildlife (Straub and Foley 2020) and the current role of nutria in the epidemiology of this disease is unclear. As the nutria population expands into new waterways with susceptible species including humans and native wildlife, continued monitoring is recommended to investigate nutria as a potential reservoir for Leptospirosis. Nutria had few ectoparasites overall. Ticks were identified as Dermacentor variabilis, a widely distributed North American tick species that been implicated in transmission of several bacterial pathogens, including Rickettsia spp. and F. tularensis (Eisen et al. 2017, Hecht et al. 2019). Fleas were identified as Pulex sp. and Orchopeas sp. Pulex sp. are a cosmopolitan species that may be a source of zoonotic pathogens, such as Bartonella spp. (Gabriel et al. 2009). Orchopeas sp. are common rodent fleas found in squirrels and woodrats and may be vectors for pathogens including Bartonella spp., Rickettsia spp. (Reeves et al. 2005), and Yersinia pestis (Davis et al. 2002) . This surveillance effort highlights the potential for nutria in California to serve as hosts for pathogens that can result in disease in humans and other animals and the importance of monitoring pathogens and parasites of invasive species within management or eradication programs. Future efforts to evaluate the role of nutria in disease transmission might include investigating additional pathogens, seasonal variations in disease prevalence, larger sample sizes, and surveys of native species sharing habitats with nutria.

Toxoplasma gondii is a zoonotic apicomplexan parasite that can cause severe morbidity and mortality in warm-blooded animals, including marine mammals like the southern sea otter (Enhydra lutris nereis). Felids, including free-ranging domestic cats (Felis catus), can shed environmentally resistant T. gondii oocysts in their feces. Contamination of nearshore waters can occur following surface runoff that mobilizes oocysts from contaminated soil to water bodies. These oocysts can concentrate in invertebrates like sea urchins, oysters, and marine snails, which are common prey for otters. Certain genotypes of T. gondii (Type X and X variants) are associated with a higher likelihood of fatal infection in sea otters, and some of these genotypes have previously been isolated from felid tissues in the greater Monterey Bay region. However, T. gondii genotypes identified in tissues may differ from parasite genotypes in feces due to the possibility of mixed T. gondii infection in free-ranging cats and variable propensity of different strains to induce substantial oocyst shedding in domestic cats. An estimated 1% of domestic cats may shed oocysts at any point in time, but studies of shedding frequency have historically focused among owned cats and in controlled (e.g., laboratory) settings. Free-ranging cats (cats that are unowned and live outdoors) have many behavioral characteristics that would make them more likely to shed compared to pet cats. There is limited knowledge on the frequency of oocyst shedding and genotypes of oocysts shed by free-ranging cats in their feces despite their large population sizes and ability to contribute to environmental oocyst contamination. Identification of specific categories of cats as sources of atypical genotypes of T. gondii associated with mortality in sea otters can help guide management actions to reduce contamination and risk of infection to endangered marine mammal populations. Therefore, we established a field study of free-ranging cats in central coastal California to understand 1) how oocyst shedding prevalence varies over time, and 2) to characterize genotypes of T. gondii shed in free-ranging cat feces. Utilizing a longitudinal field study design at four free-ranging cat colonies, we are determining oocyst shedding prevalence over a two-year period using microscopy and PCR. Samples confirmed as T. gondii using sequence analysis are genotyped using multi-locus sequence typing (MLST) at 13 polymorphic loci. Monthly fecal sampling took place between July 2020 and August 2022. Toxoplasma gondii DNA was confirmed in several samples at ~10% prevalence. Several genotypes of T. gondii have thus far been identified in the sampled feral cat feces, including atypical genotypes of T. gondii previously associated with fatal infections in sea otters (Type X and X variants). Our study helps to fill in key gaps about the contribution of free-ranging cats to environmental contamination with T. gondii and provides additional evidence of these cats as a source of atypical genotypes associated with otter deaths. Free-ranging feral cats can contribute to biological pollution of the marine environment, and proper management of these animals could play an important role in reducing environmental contamination of oocysts and subsequent T. gondii infection in endangered marine mammals.

Axis deer on the Hawaiian Islands of Maui, Lāna‘i, and Moloka‘i simultaneously experienced one of the most dramatic population crashes on record in 2020-2021, which coincided with extended drought conditions and prompted an emergency declaration for these islands. This phenomenon has been anecdotally documented during previous drought events in 2011-2012, but never formally studied. Newspaper articles document abundant deer becoming a nuisance to agriculture and natural resources, and then experiencing high mortality during droughts. This phenomenon fits Caughley’s (1970) operational definition of eruptive (sic) fluctuation “…as an increase in numbers over at least two generations, followed by a marked decline.” We examined available deer population and rainfall records over the time period of interest. Deer may have increased rapidly during favorable years with high survival and recruitment. During moderate drought, young of the year may experience high mortality, with little recruitment to populations. During severe drought, adults may experience noticeably high mortality. When populations are suppressed by large numbers of removals, fluctuations in mortality may be modulated. Abandonment of large-scale intensive agriculture in recent decades may complicate interpretation but understanding these population processes may lead to better management strategies for axis deer in Hawai‘i.

California Assembly Bill 1788 and establishment of the California Ecosystems Protection Act indicates the evolution of public opinion regarding rodent management products is moving away from the use of poison. Similar actions have taken place in the province of British Columbia and the state of Massachusetts, with initiatives in the states of Washington and Connecticut. These events signal a trend in pest management that requires attention. There are many aspects of California’s law that will require further refinements such as enforcement, best practices, and the economics of the action. The FYXX foundation 501c(3) non-profit organization has undertaken to assess these elements of alternate rodent IPM programs including any offsetting benefits of public and employee perceptions. Data was collected from three sites: two animal sanctuaries and a large commercial business district. Strategies were as follows; site #1, an IPM program including exclusion, fertility control, repellents, station monitoring with relocation and reduction (98% population reduction); site #2 IPM including fertility control, monitoring and station relocation, (80% population reduction) and site #3, IPM including station lure baiting followed by targeted fertility control, and monitoring (91% population reduction). All data were analyzed with review by professional pest managers, facility management personnel, municipal agencies, and FYXX staff. Employee interviews and surveys indicated that there was a skepticism at initiation of the study, however, by month #3 a reversal to strong support for the new program and high satisfaction with a poison-free facility. These data indicate that collaborative work between product manufacturers, professional pest managers, and users can provide new alternatives to IPM programs that are economically sound, socially, and politically responsive to a new trend in pest management.

Roof rats and other rodents are a common pest in agriculture, causing extensive amounts of damage and losses. Poultry farms provide an abundance of resources that attract rodents but our ability to control them in these locations is limited. Bait stations can become sources of nesting or go unused if the target species only travels in aerial locations. Any uncontrolled rats will quickly overpopulate agricultural buildings due to their high reproductive rates. We tested alternative baiting devices at a large poultry farm to develop a station that was easily utilized in aerial locations and well accepted by roof rats. We deployed ContraPest®, a contraceptive liquid bait, in the devices and tracked consumption monthly. We monitored the rat populations for 16 months with remote cameras to measure changes in activity before and during ContraPest baiting using a general index approach. Linear regression showed a significant relationship between ContraPest consumption and the general index. As rats continuously consumed ContraPest from the new baiting devices, activity steadily declined. Within one year of using ContraPest, rat activity reduced by 94%, showing a significant difference from starting activity levels. These results demonstrate the impact an antifertility agent can have on rat populations when used successfully within an integrated pest management program.

The Wild Free-Roaming Horses and Burros Act of 1971 provides federal oversight and protection for feral horses (wild free-roaming; WFR horses) that inhabit designated areas on public lands in the western United States. The Bureau of Land Management (BLM) estimated in 2019 that over 80,000 free-roaming equids inhabited 29 million hectares on 177 designated herd management areas. This population estimate exceeds the designated appropriate management level of 26,785. To provide BLM managers with insights regarding the U.S. public knowledge and perceptions about the management of WFR horses in the U.S., we surveyed the public using an online survey process. We hypothesized that respondents from the western U.S. would be more knowledgeable of the ecology and management of WFR horses, because of their proximity to most of the WFR horses managed in the U.S. We stratified the U.S. into five regions, with the intent to acquire at least 400 responses from each; we met this quota in four of the five regions (n of southwest = 376). Overall, the U.S. public was unknowledgeable about the ecology of WFR horses and legal management options to control their populations. While there were some associations between region, sex, age, income, and each of our questions, the strength of these associations was very weak. Therefore, demographics may not be useful in predicting the level of knowledge of the U.S. public concerning WFR horses. Our results highlight the need for improved outreach and communication efforts regarding the issues and consequences of free-roaming equid management approaches.

A robust population of endangered San Joaquin kit foxes occurs in the city of Bakersfield, CA. In March 2013, sarcoptic mange was detected in this population and the disease quickly spread. In January 2019, mange also appeared in a smaller kit fox population in the neighboring town of Taft, CA. To date there have been more than 430 confirmed cases in and 100 confirmed deaths of kit foxes. An additional 118 unrecovered individuals are presumed deceased because there is no indication that kit foxes survive without medical intervention. These numbers are also presumed underestimations of the actual number of kit foxes that have contracted and died from mange. In addition to capturing and treating kit foxes, the Endangered Species Recovery Program has conducted a yearly citywide camera survey in Bakersfield since 2015 and Taft since 2019 to assess the occurrence of mange among kit foxes and the spatial pattern of spread. Based on the Bakersfield survey, the urban kit fox population has declined by 67% since 2015. This annual camera survey also provides information on co-occurring species that could contract or transmit mange. Of the total number of cameras that have detected kit foxes with mange, 88% of those also detected at least one secondary species including raccoons, opossums, striped skunks, California ground squirrels, and domestic cats and dogs. The annual camera surveys have also detected coyotes, red foxes, gray foxes, and opossums with active mange infestations. Transmission routes for all of these species remain uncertain and the potential for transmitting mites to new areas or new individuals of multiple species is possible. Overall, mange presents a risk to multiple species in the urban environment, including domestics, for as long as it continues to circulate.

Recovery of the endangered Mount Graham red squirrel (MGRS) will likely be long and challenging. Its limited habitat, isolation to Pinaleño Mountain range, and demographic characteristics restrict its ability to rebound quickly from threats that impact both the squirrel and its habitat. Currently, threats to the MGRS include habitat degradation and loss through high-severity wildfire, fire suppression activities, insect outbreaks, climate change, and human development, and predation, as well as competition with Abert’s squirrels. The most recent wildfire in 2017 impacted over 48,000 acres of already reduced habitat. A critical first step is to protect and manage the remaining population of the MGRS and its habitat. Management includes but is not limited to maintaining and improving the spruce-fir and mixed conifer biomes, while balancing the need to reduce risk of catastrophic wildfire with the needs of the squirrel. The U.S. Department of Agriculture, Animal and Plant Health Inspection Service Wildlife Services is conducting an Abert’s Squirrel Removal Project at the request of the Arizona Game and Fish Department and the U.S. Fish and Wildlife Service (USFWS), in collaboration with a team of Mount Graham red squirrel experts and managers, to reduce the number of Abert’s squirrels in historical MGRS habitat throughout the Pinaleño Mountains to assist in meeting the needs of the USFWS’ 2011 MGRS draft recovery plan. Abert’s squirrel removals are conducted monthly to minimize competition with MGRS.

In Japan, the jungle crow (Corvus macrorhynchos) is a common problematic bird, causing significant economic damage. Previous attempts to mitigate conflict between crows and humans have generally been unsuccessful. Furthermore, it is not clear whether successful mitigation outcomes can be attributed to the effectiveness of control techniques. To directly examine the sensitivity of wild-caught jungle crows to a control technique, we observed their foraging behavior when auditory stimuli were applied to a single feeding patch (no-choice trial) or to one feeding patch but not the other (two-choice trial) in an outdoor cage. The auditory stimulus consisted of a low tone in the crow’s audible range (1 to 10 kHz), based on pink noise. In the no-choice trial, one feeding site was set up in a U-shaped experimental cage, and experiments were conducted under two conditions: 1) experimental sound presented at an 80 dB sound pressure level and 2) silence (i.e., control). In the two-choice trial, feeding sites were set up at both ends of the cage, and the auditory stimulus was presented at a sound pressure of 80 dB at only one of the feeding sites. All experiments were conducted with one individual at a time. The results of the no-choice trial showed that in the sound condition, as well as in the silent condition, all individuals started foraging in the presence of the sound, and there was no clear difference in foraging behavior between the two conditions presented. However, in the two-choice trial, the amount of food foraged in the feeding area under the silent condition was significantly higher than that in the feeding area under low-tone stimulus conditions. Our results suggest that jungle crows have relatively high noise tolerance; however, auditory stimulus is effective when an alternative foraging site is available. Further development of more complex experiments in captivity will elucidate the effectiveness of bird control techniques

Prairie dogs are an accessible and enjoyed wildlife species in Colorado that require occasional surveys because populations can change abruptly due to plague outbreaks or human-induced control. We evaluated the use of small copter drones at four prairie dog colonies on Open Space and Mountain Parks lands, City of Boulder, to determine if this methodology improves efficiency over ground-based survey methods. We counted prairie dogs and burrows using two types of drones (DJI Matric 210 and Autel Evo II) at altitudes 100', 150', and 400' (burrows only). We recorded video and merged still images into orthomosaics prior to having USDA staff analyze this imagery. We then compared the drone imagery counts to those of our simultaneous ground-based counts of prairie dogs. We determined that 100' altitude mosaics produced using DJI Matric 210 drone were most accurate (closest to true, ground-based counts) for burrow abundance. We were not able to identify the best drone and altitude combination for drone-based prairie dog abundance. Overall video and mosaics both had similar accuracy in most prairie dog counts, however 150' video was more accurate than 100' video. One staff member counted burrows more closely to true than did the other. Both staff members required about the same amount of time to count and analyze imagery; videos could be evaluated slightly faster than mosaics (average of 3.8 hours vs. 5.5 hours per imagery) when counting prairie dogs, and burrow counts (of mosaics) generally took 2-3 times longer to analyze (averaging 8.1 hours per imagery; range: 3-13 hours) than did prairie dog counts. The labor requirement of using drones for burrow and prairie dog counts is far more time consuming (3-4 times longer per hectare) than having field staff conduct the traditional on-the-ground counts that include repeated prairie dog counts in a day. Until drone technology improves to allow targeting larger colonies (>2 km2) and automated detection and counting of wildlife become more commonplace, drone surveys are unlikely to be a more efficient technique than ground-based surveys for evaluating prairie dog abundances.

Mule deer were first introduced to Santa Catalina Island, California, in the early 1930s and persist today. Other feral, non-native ungulates have been eradicated (goats, pigs) or significantly reduced in numbers (bison) over the past two decades. Effective management of the deer population is necessary to protect the island’s biodiversity but is dependent upon reliable estimates of population density and demography. We used annual summer spotlight counts, conducted in eight of the past ten years, to estimate deer densities in the island interior. In 2021, we also surveyed transects in the area around Avalon, the largest town on the island. Distance sampling (Program DISTANCE) was used to model density based on line transect data. Island-wide densities varied from 6.3 to 16.9 deer per km2, with an average of 10.2 per km2, and were positively correlated with July-June rainfall during the preceding year. Most (77-96%) of the identifiable deer were adults and most adults were does (58-75%). Deer were spotted most frequently in island chaparral and coastal sage scrub vegetation, the most common vegetation cover types along transects, whereas the use of grasslands and man-made and non-native habitats varied among years. The estimated deer density in Avalon (65.7 per km2) was six to nine times higher than estimates for the interior transects in 2021. The high density of deer near Avalon suggests that gardens, landscaping, golf courses, and intentional feeding subsidize deer numbers in town that have the potential to spill over into the more natural areas of the island.

When a large animal dies on a farm or ranch, there are often few options for disposal. In California, there are limited legal options especially as rendering facilities have closed, and both regulatory burden and the number of predators on the landscape have increased. Livestock Mortality Composting could be a viable solution to address these challenges. Composting of mammalian tissue is legal in most states and recommended for on-farm disposal of livestock mortalities but is currently illegal in California. Instead, many ranches have opted to use “bone piles” to dispose of livestock mortalities. This option has been shown to attract large predators such as wolves, mountain lions, bears and others making it a hazard for livestock operations by increasing the likelihood of livestock-predator interactions. Removing these bone piles is the number one predator attractant removal recommended by Oregon Department of Fish and Wildlife. Mammalian tissue composting is also a viable option for waste from on-farm animal processing especially as this practice has become more popular in the last few years. After navigating the regulatory oversight of multiple local and state agencies, a livestock mortality composting site was approved for research at the Intermountain Research and Extension Center in Tulelake, California. This site has composted four adult cows and demonstrated the effectiveness and safety of this process. Pile temperature was taken at 18 and 36 inches from August 2020 to January 2022. After each additional mortality, the temperature reached over 131°F for at least 72 hours to kill potential pathogens. Trail cameras were deployed at the compost site and at three nearby bone piles to compare wildlife interactions. The bone piles received on average 390 and 292 visits from predators in year one and year two respectively compared to eight visits to the compost pile. A best management practices document has been written to provide an on-farm livestock mortality composting exemption that falls within current California composting laws. This exemption could be carried out at the local, regional, or state level, although permanent changes to this policy will most likely need a legislative change.

In recent years, there has been increasing interest in the use of carbon monoxide-generating devices to control burrowing rodents. A pilot study was performed to determine how long a black-tailed prairie dog burrow needed to be fumigated with a BurrowRx® machine to obtain control. This pilot study obtained 92% efficacy with a four-minute injection, 86.7% with a 3:45-minute injection and 90% efficacy with a three-minute injection. Out of 59 burrows, 85% had only a single entrance. Of the nine that had two or more openings, six had only two, one had three openings, and two had five openings. Surface measurements from the treated opening to the furthest connected opening ranged from 10 feet to 43 feet with the average being 23.33 feet. The paper also discusses suggestions for further research and suggestions for practical use of the device.

Norbormide is a uniquely selective rat toxicant for Rattus species, with rats being 100- to 150-fold more sensitive to norbormide toxicity than most other mammals and birds. Previously we reported that on completion of a 10-year program of targeted fundamental and applied synthetic chemistry and toxicology, taste aversion associated with this compound had been overcome. In 2020-2022, trials have been successfully completed on poultry farms with Norway rats and larger scale field trials were undertaken targeting ship rats using 1% norbormide paste baits. Firstly, the efficacy of norbormide-containing paste baits targeting rat infestations on poultry farms was proven with a 100% reduction of Norway rat populations on three different farms. Secondly, 100% reduction in ship rat abundance was achieved at two large field test sites; and no reduction was achieved at the untreated control site. These larger field trials are described in depth in this publication. Plans are progressing to complete product development and registration.

Controlling small mammal pests and their damage has always been a challenge for farmers. Farmers and researchers worldwide have been experimenting with deploying nest boxes to attract barn owls to their fields to remove rodent pests. While much research has focused on the potential for nest boxes and barn owls to benefit agriculture, comparatively little work has examined the impact of the practice on owls. In this study, we used a life table analysis and estimates of barn owl reproduction measured in winegrape vineyards in Napa Valley, California coupled with published estimates of survival from long-term studies in Europe to produce a demographic model of a population of barn owls using nest boxes. We then examined how manual perturbations of survival and reproductive rates affect whether the modeled population is stable, increasing, or decreasing. Based on our empirical estimate of reproductive success and literature-sourced estimates of survival, the population appears to be growing. Across all scenarios in which we adjusted survival, there were only five that resulted in the population declining. All scenarios that resulted in population decline occurred when survival was reduced for all ages simultaneously or for adult survival independently. There were no scenarios in which lambda dropped below 1 when modifying reproductive success independent of survival. These results are important for practical pest-management reasons, as nest boxes cannot be part of a successful long-term integrated pest management (IPM) plan if they are reliant on continual immigration of adult owls from other source populations to offset mortality. A thorough examination of ecological traps should be conducted using additional information on habitat selection and reproduction in natural nest sites.

Attracting natural enemies to farms to reduce pests has long been a part of integrated pest management for insects, but knowledge of the impact of raptors on rodent and other vertebrate pests is comparatively sparse. Using wooden nest boxes to attract rodent-eating barn owls (Tyto alba and Tyto furcata) to farms has been practiced in many regions for decades, but to date there have only been a handful of studies comparing rodent numbers in the presence and absence of barn owl nest boxes, and none done within the Western United States. In this study, we surveyed rodents on winegrape vineyards in Napa California with and without occupied barn owl nest boxes by live-trapping for rodents and using the open-hole method for gophers. We collected data before the owl breeding season, when hunting pressure should be light, and again when adult owls were hunting actively to feed their chicks. We found that gopher activity declined from before to peak hunting pressure on the vineyard with barn owl nest boxes, whereas it slightly increased on the vineyard without nest boxes. Live trapping revealed that the abundance of mice declined from before to peak hunting pressure, but this decline was not significantly affected by the presence of nest boxes. Results were inconclusive for voles because they not well-sampled by our live trapping method, even though analysis of owl pellets confirmed they are an important source of prey for barn owls.

Rodenticides such as brodifacoum are more potent than first-generation anticoagulants. However, their field, farm, and outdoor use in urban settings have been linked to bioaccumulation and non-target impacts for more than three decades. Product development strategies focused on baits that yield good control of pests without residue risks to wildlife are few. To fill this gap, a bait containing a combination of diphacinone at 0.005% and cholecalciferol at 0.06% (D+C bait) has been developed as a multispecies bait for NZ use, that is effective at killing rodents and also possums (Trichosurus vulpecula), which are resistant to the toxin effects of first-generation anticoagulants. This bait was approved by the NZ Environmental Protection Agency and the product registered by the NZ Ministry of Primary Industries in 2019. A new bait is being considered with a lower dose of cholecalciferol. A bait containing half or a quarter of the loading concentration of cholecalciferol would have an even better safety profile for rodent control alone. Cage trials indicate that cholecalciferol at 0.03% with diphacinone 0.005% is as effective as brodifacoum as a single exposure bait. Amounts of cholecalciferol as low as 0.015% significantly improve the effectiveness of diphacinone.

Roof rats (Rattus rattus) are a common invasive species within the Unites States. They are very destructive in nature and are a commonly known pest within tree fruit and nut orchards in California. Tools that are used to manage roof rats in agricultural fields include rodenticides, fumigants, traps, and habitat management. However, to manage for roof rats, monitoring techniques are needed to understand the effectiveness of these management tools. Monitoring techniques that are currently used include chewing indices, snap and live trapping, remote-triggered cameras, and tracking tunnels. All of these monitoring techniques require an attractant, but uncertainty exists as to which attractants are most effective. Thus, we established a study to compare commercially available soft bait (Liphatech Rat and Mouse Attractant™) and wax block (Liphatech NoTox™) attractants to creamy peanut butter to determine their attractiveness to roof rats in citrus orchards of the southern San Joaquin Valley, California. Attractants were placed within tracking tunnels and were compared to non-baited tracking tunnels to determine potential preferences. This study was conducted across six sites in Tulare and Kern Counties, California. We generally created a 385-m × 385-m plot that contained a 10 × 10 grid structure of sampling locations at each separate orchard (n = 100 tracking tunnels at each site), although for one site we only included 96 tracking tunnels because the plot overlapped a parking area within the orchard. We used a stratified random sampling approach to determine which attractant was applied to each tracking tunnel, with an equal number of each attractant used per study site. Visitations to tracking tunnels were determined by recording the presence or absence of roof rat footprints on tracking cards located within each tracking tunnel, and we used a Fisher’s exact test to determine if visitations varied across each attractant. We determined that all three attractants increased visitation to tracking tunnels when compared to those with no attractant (visitation rate: soft bait = 54%, wax block = 57%, peanut butter = 56%, no bait = 44%; Fisher’s exact test p ≤ 0.0998). We did not observe a difference in attractiveness between any of the attractants (Fisher’s exact test p ≥ 0.721), indicating that any of the tested attractants could be used effectively. Interestingly, control tunnels without any attractant were visited at surprisingly high rates suggesting that tracking tunnels by themselves were attractive to roof rats, likely given the shelter they provide. Our findings should help citrus producers and pest control professionals more effectively monitor for roof rats in citrus orchards. Furthermore, all three tested attractants would serve as effective tools for tracking changes in roof rat numbers. Such monitoring tools are needed for testing the efficacy of management approaches. Lastly, the attractiveness of tracking tunnels even when no attractant was used suggests that this monitoring tool may result in greater detectability of roof rats when compared to approaches that do not provide shelter for rats (e.g., remote-triggered cameras), although this needs to be verified. Please see Wales et al. (2021) for additional details on this study.

Sodium fluoroacetate (1080) is a vertebrate pesticide principally used to control unwanted introduced mammals in New Zealand and Australia. For 1080, over 260 publications during the last ten years supplement a body of scientific information regarding its mode of action, natural occurrence, toxicology, antidotes, metabolism, and fate in the environment. Multi-year studies have explored long-term outcomes for multiple native bird species. Numerous reviews on community attitudes stimulated by the Predator Free New Zealand (PFNZ) 2050 campaign conclude that 1080 use for conservation remains controversial. Further effort is needed to increase target specificity, avoid game species, and employ approaches with the highest public acceptance, including hunting, trapping, and species-specific toxins. Greater acceptance of the large-scale use of any pest control is likely when long-term goals and strategies for ecosystem recovery employ toxins as one-off treatments for eradicating pests versus continued applications.