Factors Influencing the Post-Release Movements of Translocated Fishers: Implications for Translocation Success

Abstract

Long distance, post-release movements of translocated wildlife can be a key factor limiting translocation success.  Yet, for many species, we have little or no understanding of factors that influence post-release movements.  Translocations have been important for recovering fisher Pekania pennanti populations across the southern portion of their North American range.  However, little is known about the post-release movements of translocated fishers and how these movements may be influenced by demographic or translocation-process factors.  To restore fishers in Washington State, we moved 90 fishers from central British Columbia and released them at nine sites in the Olympic Fisher Recovery Area on the Olympic Peninsula of Washington from 2008 to 2010. We evaluated post-release movements of 48 fishers to determine both the distance and duration of movements prior to home range establishment.  Fishers moved extensively following their release.  Multi-model selection indicated a high level of support for the hypothesis that post-release movements differed by fisher sex and age; whereas, year of release had no apparent effect on movements, and release date had only a marginal influence on male movements.  Mean distance (± 95% CI) from a release site to a home range was greater for adult males (62.0 ± 19.6 km) than for juvenile males (31.4 ± 16.0 km), adult females (30.9 ± 21.1 km), and juvenile females (29.0 ± 13.5 km).  Mean number of days from release until home range establishment was similar for the sexes, however the variance in movement duration was greater for females.  Twenty-six of 27 females established home ranges over an 11-month period (December-October), while 19 of 21 males did so within a 4-month period (April-July).  Mean home range sizes differed between males (128.3 ± 21.1 km2) and females (63.5 ± 9.0 km2) and were among the largest reported for the species.  A greater proportion of females (18 of 27; 67%) than males (8 of 21; 38%) established home ranges within or partially within the recovery area.  Six females left a previously established home range during the breeding season, presumably to find breeding males.  Given the large distances that fishers can move following release, translocation success could be furthered by releasing individuals at fewer sites in the interior of large reintroduction areas to facilitate greater exposure to a recovery area and greater opportunity to interact with conspecifics and potential mates.