Effects of collar‐attached transmitters on behaviour, pair bond and breeding success of snow geese Anser caerulescens atlanticus

There is growing evidence that harnesses may not be an effective technique to attach radio‐transmitters on geese. The use of neck collars is an alternative, but studies on the effect of collars with or without radios on geese have reached divergent conclusions. As our objective was to determine if radio neck collars affect behaviour, pair bonds and breeding success of greater snow geese Anser caerulescens atlanticus , we fitted 230 females with radio neck collars during the 1995–1998 moulting periods on Bylot Island, Nunavut. Data were subsequently obtained for 159 birds on the staging and breeding grounds. Radios represented 2.5 ± 0.1 % (± SE) of the birds' body mass. Unmarked geese and those fitted with conventional plastic collars served as controls. The behaviour of radiocollared geese was affected during the first fall after marking, but negative effects disappeared thereafter. Geese with conventional collars had similar behaviour as unmarked birds. Divorce rates were low for birds with conventional collars (0–4%), but were as great as 30% for radio‐collared geese. We suggest that the modified behaviour of the radio‐collared females promoted separation from the male. Apparent breeding propensity, nest initiation date, clutch size and nesting success of radio‐marked birds were also negatively affected. Until better alternatives are developed, we recommend minimizing the mass of radio collars to < 2.5% of the birds' body mass and reducing the antenna length. This implies a trade‐off between effects on birds and performance of the transmitters in terms of battery mass (longevity) and antenna length (range).