Rabies Management Implications Based on Raccoon Population Density Indexes

Authors

Dennis Slate, USDA, APHIS & Chippewa Bay Wildlife Art and Science LLC
Brandi D. Saidy, USDA, APHIS
Ashlee Simmons, USDA, APHISFollow
Kathleen M. Nelson, USDA, APHIS
Amy Davis, USDA, APHIS
Timothy P. Algeo, USDA, APHIS
Stacey A. Elmore, USDA, APHIS & VCA Veterinary Specialist of Northern Colorado
Richard B. Chipman, USDA, APHIS

ORCID IDs

http://orcid.org/0000-0002-9682-3401

Document Type

Article

Date of this Version

2-16-2020

Citation

Slate, D., B.D. Saidy, A. Simmons, K.M. Nelson, A. Davis, T.P. Algeo, S.A. Elmore, and R.B. Chipman. 2020. Rabies management implications based on raccoon population density indexes. The Journal of Wildlife Management 84(5):877-890. doi: 10.1002/jwmg.21869

Abstract

An estimate or index of target species density is important in determining oral rabies vaccination (ORV) bait densities to control and eliminate specific rabies variants. From 1997–2011, we indexed raccoon (Procyon lotor) densities 253 times based on cumulative captures on 163 sites from Maine to Alabama, USA, near ORV zones created to prevent raccoon rabies from spreading to new areas. We conducted indexing under a common cage trapping protocol near the time of annual ORV to aid in bait density decisions. Unique raccoons (n = 8,415) accounted for 68.0% of captures (n = 12,367). We recaptured raccoons 2,669 times. We applied Schnabel and Huggins mark‐recapture models on sites with ≥3 years of capture data and ≥25% recaptures as context for raccoon density indexes (RDIs). Simple linear relationships between RDIs and mark‐recapture estimates supported application of our 2 index. Raccoon density indexes ranged from 0.0–56.9 raccoons/km . For bait density decisions, we evaluated RDIs in the following 4 raccoon density groups, which were statistically different: (0.0–5.0 [n = 70], 5.1–15.0 [n = 129], 15.1–25.0 [n = 31], and >25.0 raccoons/km2 [n = 23]). Mean RDI was positively associated with a higher percentage of developed land cover and a lower percentage of evergreen forest. Non‐target species composition (excluding recaptured raccoons) accounted for 32.0% of captures. Potential bait competitors accounted for 76.5% of non‐targets. The opossum (Didelphis virginiana) was the primary potential bait competitor from 27°N to 44°N latitude, north of which it was numerically replaced by the striped skunk (Mephitis mephitis). We selected the RDI approach over mark-recapture methods because of costs, geographic scope, staff availability, and the need for supplemental serologic samples. The 4 density groups provided adequate sensitivity to support bait density decisions for the current 2 bait density options. Future improvements to the method include providing random trapping locations to field personnel to prevent trap clustering and marking non‐targets to better characterize bait competitors.