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Field-edge habitat is important for enhancing biodiversity and associated ecosystem services on farms for long term agricultural sustainability. However, there is some concern that this habitat will increase wildlife activity and damage to adjacent crops. Wildlife incursion into production areas may also pose food safety risks. A two-year study in walnut orchards and processing tomato fields in the Sacramento Valley, California, documented variable use of farm fields by mammalian wildlife. This depended on field-edge habitat (restored hedgerows versus conventionally managed field edges where vegetation was mostly controlled), wildlife species present, season, and crop monitored. In walnut orchards, deer mice (Peromyscus maniculatus Wagner, 1845) were found throughout the orchard, while house mice (Mus musculus Linnaeus, 1758) exclusively used hedgerows. In tomato fields, deer mice were more common in field interiors during spring, but used field-edge habitats more during summer; the opposite was true for house mice. In general, deer mice preferred more open sites, while house mice were most numerous in areas with thick cover. Both desert cottontails (Sylvilagus audubonii Baird, 1858) and black-tailed jackrabbits (Lepus californicus Gray, 1837) showed affinity to hedgerow portions of fields, although this association was stronger for cottontails. Overall, we documented greater mammalian species richness and abundance associated with hedgerows. However, this increase in diversity did not generally lead to greater wildlife incursion into adjacent crops. In walnut orchards, Salmonella and non-O157 STEC were detected from 2 (1%) and 4 (2%) individual rodents, respectively (n = 218); no detections occurred in tomato fields. A subset of fecal samples (n = 87) from rodents captured in walnut orchards were positive for Giardia (25%) and Cryptosporidium (24%) but prevalence was not associated with field-edge habitat type. Overall, there does not appear to be a substantially greater risk of crop loss or contamination of foodborne pathogens in crops bordered by hedgerows in our study in the Sacramento Valley, although potential damage could vary by the stage and type of crop and wildlife species present.

Feral swine were targeted for and successfully eradicated from Saint Vincent Island (SVI), a National Wildlife Refuge (NWR) along the coast of Florida's panhandle to protect its habitats and uncharacteristically high diversity of wildlife species for barrier islands in the region, including federal and state-listed threatened and endangered species. The eradication effort was initiated in early 2015 and concluded in 2019. A total of 438 feral swine were removed from the Island, 417 by federal control experts and 21 by recreational hunters. In general, the amount of effort needed to eradicate each feral swine slowly increased as the eradication effort progressed; however, effort increased by an order of magnitude in the final six months. The last three feral swine took 77 days of effort to remove. The eradication effort provided an opportunity for evaluating and comparing methods for indexing feral swine population abundance and their abilities to describe population trends and to detect animals at low population abundance. The feral swine population was monitored from 2015–2019 using a passive tracking index (PTI) twice each year and using camera traps. Camera and track plot data were used to calculate abundance indices based on a well-documented indexing paradigm applied to feral swine populations. In addition, we simultaneously monitored relative abundance of other mammalian species crucial to management for the Island. The PTI and camera index both well-tracked population abundance simultaneously for the large ungulates inhabiting the Island (feral swine, white-tailed deer, sambar deer). However, the sensitivity for the PTI to capture animal observations was much greater than for the camera stations. This held true even over 5-day observation sessions by cameras versus 3-day observation sessions for track plots. Additionally, the PTI was sensitive for simultaneously capturing data for smaller animals, raccoons and armadillos, whereas the camera stations were ineffective for the smaller species, likely due to camera positions being optimised to capture feral swine. Our 100-m track plots outperformed the camera stations in many regards, but the camera stations required less labour in the field and were less fragile in the field, especially from weather or access issues. In 2018, Hurricane Michael, a category 5 hurricane, struck SVI. Its habitat damage may have adversely impacted white-tailed deer and sambar deer populations, but not armadillos or raccoons. Both the swine eradication and hurricane impacts provided valuable means for validating indexing procedures. [ABSTRACT FROM AUTHOR]

This one-year study focused on the impact of hedgerows of native California plants on rodents and food safety in adjacent crops in the Sacramento Valley. Deer mice, house mice, California voles, and western harvest mice were live trapped in four different walnut orchards at zero, 10, 75, 175-m transects from hedgerows. The abundance and richness of rodents was compared to control sites with conventionally managed field edges that were mowed or sprayed for weed control. Unique rodent capture data showed two peaks in activity: 1) in the middle of the orchard regardless of field border type, and 2) in the hedgerow across all seasons with winter being the most active overall. Fewer captures were recorded in the conventional field border, likely because they lacked vegetative structure. Deer mice were the most prevalent species captured throughout the study (>96% of unique captures). House mice and California voles were almost always found in hedgerows and not in adjacent crops. Fecal samples from captured rodents showed a low prevalence of Escherichia coli (non-O157 STEC 1.4%, n = 438; O157 STEC 0%, n = 434) and Salmonella (0.92%, n = 434). Giardia (28.6%, n = 210) and Cryptosporidium (23.8%, n = 210) were more prevalent in captured rodents, but the distribution was not affected by field-edge habitat.

Roof rats and deer mice are occasional pests of orchard crops throughout the world. The application of rodenticides is an effective and practical method for controlling rodent pests and reducing damage. However, a paucity of information exists on the efficacy of rodenticides in orchards for these pest species. To address this gap in knowledge, we first developed an index to measure rodent activity in order to monitor efficacy of rodenticides. We then used this index to test the efficacy of 3 first-generation anticoagulant rodenticide baits to determine their utility for controlling roof rats and deer mice in agricultural orchards. Of the baits tested, the 0.005% diphacinone grain bait was the most effective option for controlling both roof rats and deer mice (average efficacy = 90% and 99%, respectively). The use of elevated bait stations proved effective at providing bait to target species and should substantially limit non-target access to rodenticides.

Lettuce is an important economic crop in California, with approximately 101,000 ha in production and a value of $1.3 billion in 2002. Bird damage to lettuce in the San Joaquin Valley, the central coast, and southern California is believed to amount to millions of dollars annually. We evaluated the effectiveness of Flight Control™ (50% anthraquinone applied at 10 L/ha) as a foliar spray for protecting emerging lettuce seedlings from depredation by horned larks. In field enclosure trials conducted near Huron, in the San Joaquin Valley of California, damage to treated lettuce seedlings was 8.5%, compared to 68% damage to untreated seedlings. In a field test, anthraquinone residues on the day of treatment averaged 570 ppm and at Day 50 after treatment were lower than the method of detection (0.063 ppm). However, horned lark numbers using test sites were too low to detect any differences in damage among treated and untreated sites. Anthraquinone offers promise for reducing bird depredations to sprouting lettuce, but additional testing should be conducted to evaluate this repellent in a large-scale field setting.

This paper presents a general summary of an economic assessment of the United States Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS), Wildlife Services (WS) Program in California (CA). Detailed analyses quantified WS economic benefits to each of the 38 counties that contributed cooperative funds in 2004, with an aggregate report of county results used to form an overall statewide estimate of the Program’s value. Four general categories of wildlife damage management activities were: Agriculture, Health and Human Safety, Natural Resources, and Property. Two general methods of determining economic valuation were employed to quantify benefits: replacement-cost method, and damage-avoided method. Results showed that the protection of livestock, particularly sheep, cattle, and goats, from predation was a main activity of WS–CA personnel in each of the cooperating counties. Annual estimated replacement costs for WS–CA operations for Year 1 and Year 2 of the analysis (i.e., approximately equivalent to fiscal years 2003 and 2004, respectively) totaled $6,605,234 and $8,602,590 for the combined counties, respectively. Mean replacement costs for WS operations in the cooperating counties in Year 1 and Year 2 equaled $173,821.95 and $226,373.13, respectively. Given that the counties paid an average $51,798.10 share to WS–CA in 2003, the counties would have incurred averaged net increased expenses of $122,023.85 and $174,575.03 for similar services offered by commercial wildlife damage management companies.

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.

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

Trapping records from studies conducted in Hawaiian sugarcane fields were analyzed to determine the effects of rat captures on subsequent capture success of Rattus norvegicus, R. rattus, and R. exulans. Traps that captured rats were subsequently more likely to capture another rat of the same species. We detected no differences in trap responses of males and females, nor did we observe any evidence that capture success of Polynesian rats and roof rats was affected by previous captures of Norway rats. This increased trap success may have been due to residual trap odors, or to greater success of traps set in optimal locations. Researchers should exercise caution in interpreting trapping results, and take precautions to eliminate residual trap odors due to previous captures. A better understanding of the effects of congeneric odors on the trapability of rats could lead to the development of more attractive and selective bait formulations, improved trapping techniques, and better interpretation of research results.

The effectiveness of bait and the effectiveness of operational baiting were both evaluated for controlling forest pocket gophers (Thomomys spp.) with strychnine oat groat bait and diphacinone paraffin block bait. Radio-telemetry monitoring and recovery of pocket gophers showed that control of individual pocket gophers 1 month after baiting was 72% for strychnine bait and 62% for diphacinone bait. Reduction in pocket gopher activity from operational baiting was based on censusing activity in sample plots. After 1 month the reduction in activity was 61% for strychnine oats and 36% for diphacinone blocks. Bait blocks implanted with radio transmitters were extensively moved and fed on by pocket gophers. Pocket gopher activity was not significantly reduced by either treatment 6 months or 1 year after baiting.

Radio-telemetry evaluation of several concentrations of pelleted strychnine bait in earlier tests indicated moderate to good bait efficacy for control of mountain beavers. Evaluation of operational baiting with 0.0%, 0.15%, 0.50%, and 0.90% strychnine bait pellets was made in 1990 and 1991 on 24 reforestation units in Washington and Oregon. Results of baiting monitored with burrow activity indicators showed there was little difference in reduction of activity among treatments. Chemical assays and pen bioassays showed baits were lethal, but ingestion was often delayed or baits were discarded. Reexamination of test plots 1 year after baiting showed no detectable change in activity among treatments.

A laboratory study was conducted in which tissues from zinc phosphide-killed black-tailed prairie dogs (Cynomys ludovicianus) were fed to domestic ferrets (Mustela putorius). Prairie dogs were fed a 2.03% zinc phosphide bait and upon death, two tissue complexes were prepared: stomach, liver, and intestines, and the remaining carcass. Five male and five female ferrets were each fed one of the two treated tissue complexes. A similar number of ferrets were each fed one of the two control tissue complexes. No poisoning symptoms or emesis were observed and no ferret mortality occurred. Zinc phosphide residue was determined in 10 prairie dog carcasses; 99.9% was found in the stomachs and small intestines. Residues were also detected in the large intestine, caeca, kidneys, and gall bladder/liver, none were found in the lungs, heart, or muscle. The low amounts of zinc phosphide remaining in the carcasses, the absence of ferret mortality, poisoning symptoms or emesis, despite the emetic properties of zinc phosphide, confirm that the risk of secondary poisoning from zinc phosphide is unlikely.

Laboratory tests, field telemetry trials, and actual use field efficacy evaluations showed that a 0.5% strychnine alkaloid steam-rolled oat-groat hand-bait formulation (EPA Reg. No. 56228-20) with molasses, salt, glycerine, and soda was effective in controlling northern pocket gophers (Thomomys talpoides). Baits retaining at least 0.5% strychnine (w/w) were as effective (>95% control) as baits with 0.75% and 1.0% strychnine in field telemetry hand-baiting trials as well as operational hand-baiting and burrow-builder baiting field tests in forest habitat. Data indicated that the 0.5% strychnine hand bait (molasses formulation) should be reregistered and would be a good substitute for the 0.5% strychnine-Rhoplex bait (EPA Reg. No. 5622812) currently registered for burrow builder use for pocket gopher control. Both the retention of strychnine on bait and use of a highly palatable top quality bait carrier were two important factors affecting efficacy of the bait.

Seasonal responses of captive coyotes (Canis latrans) to 9 chemical attractants (W-U lure, TMAD, SFE, FAS, CFA, artificial smoked fish flavor, artificial beef liver flavor, yeast autolysate and decanoic acid) were evaluated. Twenty-six additional attractants were tested only during the summer. W-U lure and FAS produced the greatest total response times from coyotes during all seasons of the year. FAS and smoked fish flavor evoked the most lick-chew-bite and pulling behaviors during the summer and have potential for improving the performance of M-44 devices in warm weather.