Natural Movements of Beavers in Southeastern Idaho

Abstract

One hundred and ninety-two beavers (Castor canadensis) were livetrapped and tagged in order to determine the origin of troublesome beavers on private lands. Data from 87 retrapped animals showed that 19 had moved at least 1 mile in 7to 28-month periods and the 19 moves averaged 5.3 airline miles. An adult male moved 11.3 miles, the longest recorded. Of the limited sample, the yearling age-class, and the males of all age groups, showed the greatest migration tendencies. Evidence from one colony indicated that some beavers have an innate tendency to leave their home colony when about 2 years old, rather than being driven off by their parents. The common migration pattern was from high elevation public land to private holdings downstream where beaver structures caused flooding of crops, pastures, and roads, and the interruption of irrigation and stock-watering systems. Beavers perennially cause problems for ranchers, farmers, and highway crews in Bear Lake and Caribou counties in southeastern Idaho. Long trapping seasons and vigilant conservation officers assure that the majority of beavers in complaint areas are annually eliminated. However, beavers soon move in to fill the vacancies. In 1962 a study was initiated to determine the productivity and origin of these migrants (Leege 1964). The productivity data have already been reported (Leege and Williams 1967). Thanks are extended to Dr. Paul D. Dalke, Idaho Cooperative Wildlife Research Unit, and Roger M. Williams, Idaho Fish and Game Department, for their counsel throughout the study and for reviewing this manuscript. John Kindall assisted with the livetrapping and provided most of the tag returns through his fur trapping activities.