An evaluation of territory mapping to estimate fisher density

Abstract

We evaluated winter-territory mapping as a method for estimating fisher (Martes pennanti) density in a 210-km2 survey area in north-central Massachusetts in 1994 and 1995 by comparing estimates with simultaneous camera mark–resight estimates. Assuming intrasexual territoriality and accounting for all occupied habitat, territories of resident radio-marked fishers were mapped (mean = 54% of all territories in the study area), and those of unmarked resident fishers were identified from tracks and photographs. The total number indicated a population of 40 (19/100 km2) and 49 (23/100 km2) residents for 1994 and 1995, respectively. Results from replicated automatic-camera capture–mark–resight surveys suggested slightly higher total numbers and densities of fishers in 1994 (44.5; 21/100 km2) and 1995 (52.9; 25/100 km2), but these estimates likely also included nonresident juveniles. Territory mapping and automatic-camera mark–resight methods resulted in very similar population estimates, but both require large numbers of radio-marked fishers to effectively detect small population changes (e.g., such as the 20% observed in this study). Individually marking animals would enhance mark–recapture estimates.