Alphachloralose sedation for capture of Canada geese (Branta canadensis) : a dissertation submitted in partial fulfilment of the requirements for the Postgraduate Diploma in Applied Science at Lincoln University

Abstract

Chemical control using the sedative alphachloralose (AC) could be a useful technique for managing Canada geese (Branta canadensis) where they are overabundant on New Zealand farmland. In North American trials, Canada goose control using AC appears promising. However, recent New Zealand field trials where flocks of geese have been baited with AC have been relatively unsuccessful due to geese leaving the trial site before being adequately sedated.

A pen trail was undertaken using 83 moulting Canada geese captured from Lake Ellesmere, Canterbury. The aim of this trial was to establish if the AC dose found effective in the American studies (30 mg AC/kg body weight) was adequate under New Zealand conditions. Four groups of 20 geese were exposed to grain containing AC at concentrations ranging from 0.20% to 1.06%. Mean consumption of drugged bait ranged from 16.1 g to 38.1 g per goose, resulting in mean doses of 22.2 to 48.8 mg AC/kg body weight. The proportion of geese effectively sedated ranged from 25% to 86%. However, individual geese within each group varied markedly in their bait consumption. Possible reasons for failure of the previous New Zealand field trials include: • geese may have been leaving the baiting site in search of drinking water; • AC loading was not high enough, and/or bait consumption was too variable, for most geese to receive an effective dose; • feeding bait out in lines (cf. separate piles in North America) may have caused increased social interaction between geese which disturbed lightly sedated individuals and caused them to take flight before receiving an effective dose.

It was concluded that further field trials with alphachloralose are warranted to try and improve the efficacy of the method in New Zealand. A series of recommendations for the conduct of these field trials are provided.