Field immobilization and use of radiocollars on long-tailed weasels

Using radiocollars to conduct relatively long-term studies of weasels (Mustela spp.) is problematic because individuals shed collars frequently and because collars may induce behavioral changes. During 1998-1999, we immobilized 16 free-ranging long-tailed weasels (Mustela frenata) using 25-mg/kg ketamine hydrochloride and 2-mg/kg xylazine hydrochloride. Mean induction time was 2 minutes and time to first arousal averaged 26 minutes. We fitted 9 male and 6 female weasels with 6.5-g and 3.2-g tuned-loop radiocollars, respectively. Of these, we observed 5 males and 2 females in captivity under semi-natural conditions. Radiocollars did not appear to influence weasel use of burrows and coarse woody debris or compromise their ability to kill prey. In the field, 8 of 9 males and all females retained collars more than one week. Males were tracked for a mean of 62 days (range= 5-158 days), whereas females were tracked for a mean of 51 days (range=8-108 days). Radiocollars did not appear to adversely affect foraging or reproduction of tagged weasels.