TECHNICAL NOTE Wildl. Biol. Pract., 2013 June 9(1): 7-13 doi:10.2461/wbp.2013.9.2 Copyright © 2013 L. Gorini, S.J. Wedul, J.M. Arnemo, J.D.C. Linnell, L. Boitani, E.B. Nilsen. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distri- bution, and reproduction in any medium, provided the original work is properly cited. Published by: Portuguese Wildlife Society. Field Anesthesia of Least Weasels (Mustela nivalis nivalis) with Isoflurane L. Gorini 1,2,* , S.J. Wedul 1 , J.M. Arnemo 1,3 , J.D.C. Linnell 2 , L. Boitani 4 , E.B. Nilsen 2 1 Department of Forestry and Wildlife Management, Faculty of Applied Ecology and Agricultural Sciences, Hedmark University College, Campus Evenstad, NO-2418 Elverum. 2 Norwegian Institute for Nature Research, NO-7485 Trondheim, Norway. 3 Department of Wildlife, Fish and Environmental Studies, Faculty of Forest Sciences, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden. 4 University of Rome “La Sapienza”, Department of Environmental Biology, V.le dell`Università 32, 00185 Rome, Italy. * Corresponding author address: Department of Forestry and Wildlife Management, Faculty of Applied Ecology and Agricultural Sciences, Hedmark University College, Campus Evenstad, NO-2418 Elverum; e-mail: lucrezia.gorini@hihm.no. Keywords Anesthesia; Least Weasel; Nest Box; Portable Anesthesia Unit. Abstract The aggressive and agile nature of weasels makes the use of inhalant anesthetics preferable to injectable agents because inhalant anesthetics generally reduce handling time, cause less stress and present no risk of delivering the drug into an unintended area. Here we report on the use of the inhalant anesthetic isolurane in free ranging least weasels. We used a battery powered portable anesthesia unit (Uninventor 400 Anesthesia Unit, AgnTho’s AB, Sweden) to immobilize the animals in the ield. The isolurane liquid was illed in a syringe connected to a vaporizer where it mixed with air coming from an air pump. The animals inhaled the anesthetic irst in a wooden chamber and then through a modiied facial mask. Mean induction time in the anesthetic chamber was 4.8 minutes (± 0.3 SE) with a setting of 4% isolurane. The anesthesia was maintained with the facial mask and a setting of 2% isolurane. Mean recovery time was 16.4 minutes (± 2.1 SE) and mean recumbency time 40.7 minutes (± 2.9 SE). We anesthesized 9 animals, had no fatalities during anesthesia and all animals recovered quickly. One animal was found dead 11 days post-capture of undetermined cause. Isolurane is safe and easy to use with the tested setting. However we were unsuccessful in monitoring the animals following their release and we therefore recommend further evaluation of the anesthetic. In addition, we recommend the use of a wooden anesthetic chamber with bedding to avoid the risk of hypothermia. Introduction Predation by stoats (Mustela erminea) and weasels (M. nivalis) may have a strong impact on the population dynamics of their prey [1, 2]. Habitat use and hunting behavior of these species have however, mostly been studied using capture-mark-recapture methods, hair-traps, tracking tunnels (two-openings tunnels with paper and ink on the bottom where weasels´ tracks are left after the passage of the animals) or snow- tracking [3, 4]. Few studies have been based on radio-telemetry [but see for example 5], a research method that is often more effective [3] but which requires the anesthesia of captured individuals. A large number of anesthetics have been used in studies on small mustelids: e.g. ether [6, 7], phencyclidine hydrochloride and promazine [8] and ketamine [9]. Some of them are no longer in use or no longer produced (e.g. ether and phencyclidine). Others, such as ketamine, have the disadvantage of causing