Errors associated with moose-hunter counts of occupied beaver Castor fiber lodges in Norway

Abstract

In Norway, Sweden and Finland moose Alces alces hunting teams are often employed to survey occupied beaver (Castor fiber and C. canadensis) lodges while hunting. Results may be used to estimate population density or trend, or for issuing harvest permits. Despite the method’s increasing popularity, the errors involved have never been identified. In this study we 1) compare hunting-team counts of occupied lodges with total counts, 2) identify the sources of error between counts and 3) evaluate the method’s management potential. The study was conducted in Bø Township (266 km²), Telemark County, Norway during 1995. Hunters reported the number of occupied lodges seen daily while hunting moose (25 September - 31 October). Teams (n = 12) under-counted occupied lodges in the township by 62% because 1) the probability of observing an occupied lodge within areas actually hunted on was 0.77, 2) 37% of the moosehunting units were not hunted on and 3) 21% of the occupied lodges occurred in cultivated landscapes outside of moose-hunting units. Hunters had difficulty distinguishing between occupied and unoccupied lodges. Measures of precision and bias should be determined before using the method for practical management. Moose-hunting team surveys may be better suited for obtaining indexes of population change than estimates of occupied lodge number.