A comparison of methods for estimating raccoon abundance: Implications for disease vaccination programs

Abstract

Accurate estimates of demographic parameters are critical to the management of wildlife populations, including management programs focused on controlling the spread of zoonotic diseases. Rabies managers in the United States Department of Agriculture (USDA) have applied a simple raccoon (Procyon lotor) abundance index (RAI) based on cumulative catch of unique raccoons per unit area to determine vaccine‐bait distribution densities. This approach was designed to allow for both the collection of biological samples and to index raccoon abundance to determine bait densities for oral rabies programs. However, post‐baiting surveillance data indicate that, on average, only 30% of raccoons sampled have vaccine induced rabies antibody titers, suggesting that bait densities may not be well calibrated to raccoon densities. We trapped raccoons using both capture‐mark‐recapture (CMR) and the standard RAI to evaluate the accuracy of the current index‐based methodology for estimating raccoon density. We then developed a resource selection function from spatial data collected from radio‐collared raccoons to standardize trap placement within the existing RAI protocol, and evaluated the performance of this modified RAI approach relative to CMR for estimating raccoon population size. Both abundance and density estimates derived using the RAI consistently underestimated raccoon population sizes compared with CMR methods. Similarly, although the use of resource selection models to inform trap placement appeared to improve the accuracy of the RAI, the effectiveness of this method was inconsistent because of an inability to account for variance in detection probabilities. Despite the logistical advantages of using indices to estimate population parameters to determine vaccine bait distribution densities, our results suggest that adjustments may be necessary to more accurately quantify raccoon abundance, which should improve the effectiveness of rabies management in the United States. In particular, estimates of detection probabilities are needed to more precisely quantify abundance estimates and ensure appropriate vaccine coverage rates. © 2012 The Wildlife Society.

Local People’s Perceptions of Crop Damage by Common Langurs (Semnopithecus entellus) and Human-langur Conflict in Keshabpur of Bangladesh

“…Fruits such as, mango, jackfruit, guava, black berry, and litchi were mostly damaged during the fruiting season, whereas other types of fruit (e.g., banana, papaya, sapodilla, hog plum, and immature coconut) were damaged throughout the year. This suggests that the crop-raiding patterns by langurs in Keshabpur might be determined by seasonal aspects of the available human-edible fruits, rather than by the scarcity of foods, as observed in several previous studies (e.g., (Beasley & Rhodes, 2008;Chiyo, Cochrane, Naughton, & Basuta, 2005;Sukumar, 1989).…”

Rabies Management Implications Based on Raccoon Population Density Indexes

“…The disparity between RDIs and Huggins estimates generally increased at higher raccoon abundance. In a comparison study exploring calibration of RDIs, Beasley et al (2012) reported that on average RDIs used by Wildlife Services were 48% lower than mark‐recapture estimates in fragmented agricultural areas in north‐central Indiana, USA. However, from a rabies management perspective, 20 of our 26 density groups aligned with bait densities suggested by both mark‐recapture estimates.…”

Spatiotemporal dynamics of mesocarnivore populations

“…It is large, mature trees, as a critical habitat attribute, that provide raccoons with sufficiently large tree cavities for reproduction and denning (Chamberlain et al 2002, Henner et al 2004. Abundance of female raccoons was positively related to den tree density in the agricultural landscape of north central Indiana, USA (Beasley et al 2012). Raccoons are the effective predators of avian nests and small mammals, and also scavenge for food from human residence in the rural areas.…”

“…It is reasonable to expect raccoon populations increase in the landscape disturbed by human residential establishment and agriculture owing to enhanced food availability (Beasley et al 2011, Troyer et al 2014b. With increasing raccoon population size and limited number of mature trees for maternal denning, raccoon populations may become density dependently regulated and become stabilized at the carrying capacity (Beasley et al 2012). Raccoon populations reached an equilibrium with the finite rate of increase being stabilized at 1.0 in a protected area in Florida, USA (Troyer et al 2014b).…”

“…Long-term relative abundance indices, such as spot light survey count, harvest indices (often without harvest effort), and capture per unit effort from hunting bags and hunter's efforts like those used in this study, provide a useful source of multiple long-term time series of relative abundance (Rolley and Lehman 1992, Beasley et al 2012, Hagen et al 2014. However, we caution that relative abundance indices may underestimate population abundance (Beasley et al 2012, Leclerc et al 2016. Capture per unit effort is assumed to be positively related to true population abundance.…”