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.

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.

Trimethacarb (2,3,5-trimethylphenyl methycarbonate) was evaluated as a mouse repellent in no-till corn plantings. Two studies were conducted. One involved an early spring planting and included 5 treated and 5 control plots. The second involved a late spring planting and included 3 treated and 3 control plots. Species composition and relative abundance of small mammals were determined for each plot by trap and release before treatment. On the 10 early spring plots, species composition was 85% prairie voles (Microtus ochrogaster), 14% deer mice (Peromyscus spp.), and 1% house mice (Mus musculus). On the 6 Iate spring plots, species composition was 66% prairie voles, 28% deer mice, and 6% house mice. Trimethacarb (15% by weight) was applied in a 15-20 cm band on the ground surface over the planted corn seed at a maximum rate of 9.2 kg/ha. Corn seeds consumed by small mammals and intact corn sprouts were counted when the corn was approximately 10 cm tall, or about 17 days after planting. At harvest, the numbers of corn stalks and yield in kg per ha were estimated. In the early spring planting, mice consumed a total of 657 and 755 seeds on the 200 sampling sites (treated and control plots, respectively). In the late spring planting, mice consumed a total of 122 and 87 seeds on the 120 sampling sites (treated and control plots, respectively). Differences between the mean numbers of seeds consumed by mice on the treated and control plots were not statistically significant in either planting. In the early spring plantings, a total of 1,784 and 1,641 intact sprouts were present on the 160 sampling sites {treated and control plots, respectively). In the late spring plantings, a total of 1,267 and 1,114 intact sprouts were present on the 120 sampling sites (treated and control plots, respectively). Differences between the mean numbers of intact sprouts on the treated and control plots were not statistically significant in either planting. The average numbers of stalks per ha at harvest for the early spring planting were 42,230 and 31,604 (treated and control plots, respectively); estimates for the late spring planting were at 42,929 and 40,597 (treated and control plots, respectively). Differences between the numbers of stalks on the treated and control plots were not statistically significant for either planting. Average yield for the early spring planting was 8492 kg/ha and 6267 kg/ha (treated and control plots, respectively); and for the late spring planting was 6618 kg/ha and 6831 kg/ha (treated and control, respectively). There was no statistically significant difference in kg/ha between treated and control plots for either planting. These results indicate that trimethacarb is not an effective mouse repellent in no-till corn plantings.

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.

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.

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.

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.

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.

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.

A field study of unpadded and padded foothold coyote traps was undertaken in six western states in 1986-1987. Tests were designed to determine the capture efficiency and extent of foot injury caused by different trap modifications. Results were similar to an earlier study undertaken in 1984-85 that showed padded traps reduced foot injury but captured and held fewer animals than did unpadded traps. Both studies showed that unpadded long-spring traps used operationally by Federal Animal Damage Control specialists were the most effective (75-78% capture rate) but caused more foot injury. Padded long-spring traps were intermediate in efficacy (52-57%) and foot injury, while padded "Soft Catch''™ traps were the least effective (30-58%) but caused the least injury to captured coyotes.