U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version

January 2003


Proceedings from the 10th Wildlife Damage Management Conference. (K.A. Fagerstone, G.W. Witmer, Eds). 2003.


Methods to better quantify beaver (Castor canadensis) population size need to be developed to assist in the direct control methods being implemented by Wildlife Services. Many state game and fish departments rely on lodge counts, cache counts, or fur harvest reports to estimate a station-wide or regional population of beaver. However, Wildlife Services is concerned with estimating population size on a per site basis to assist in estimating project costs and to minimize the number of non-target captures. Six sites in Mississippi were selected to test various methods of population estimation. Various methods included indexing population size based on the amount of sign and physical site characteristics, and spotlighting beaver to derive estimates based on actual counts, extrapolations, and the Lincoln-Petersen model. All derived estimates were compared to number of beaver captured during total harvest. Number of lodges, bank dens, and beaver dams were not significantly related to total harvest. Number of scent mounds was positively correlated with total harvest; however, number of scent mounds was not significant. Area and perimeter distance of each site was positively correlated with total harvest of beaver. Spotlight counts were conducted from the bank of each site and from a boat and only combined for data analysis. Research indicated that managers and wildlife biologists should use caution and expect differences when spotlighting beaver. A combination of actual numbers of beaver viewed during bank counts and boat counts was significantly correlated to total harvest. Overall, spotlighting beaver for population estimates was determined to be an ineffective technique.