Assessment of habitat-specific competition for oral rabies vaccine baits between raccoons and opossums

Throughout the eastern United States, the National Rabies Management Program (NRMP) distributes oral rabies vaccine (ORV) baits to manage rabies virus circulation in raccoon (Procyon lotor) populations. The consumption of vaccine baits by non-target species including Virginia opossums (Didelphis virginiana) may reduce the effectiveness of ORV programs, but competition for baits remains poorly quantified in many areas of the southeastern United States. We distributed placebo ORV baits injected with a biomarker across 4 land cover types (bottomland hardwood, upland pine, riparian, isolated wetland) on the Savannah River Site in South Carolina, USA, 2017-2019. We then trapped and collected whiskers from 247 raccoons and 78 opossums to assess biomarker presence using fluorescent microscopy. Our data revealed greater bait uptake probability by raccoons (estimated x(-) = 0.30, 95% CI = 0.19-0.44) compared to opossums (estimated x(-) = 0.11, 95% CI = 0.05-0.23) across all cover types surveyed. Probability of bait consumption was not affected by cover type or the abundance of raccoons or opossums. Among raccoons, males were more likely to consume baits than females (estimated x(-) = 0.28, 95% CI = 0.17-0.44 for males and 0.14, 95% CI = 0.05-0.31 for females) and probability of consumption increased by 0.08 with each additional day trapped during the 10-day trapping session. Uptake rates for raccoons were relatively low compared to other studies and not influenced by competition with opossums. These low consumption rates indicate that additional research addressing the roles of baiting season, bait density, and resource selection will be important to maximize ORV bait uptake by target species in these southeastern landscapes.