Year-long deployments of small geolocators increase corticosterone levels in murres

Abstract

Geolocators provide information on the year-round movements of birds. The effect of the year-round deployment of such devices has, however, largely been examined via measures that are relatively insensitive to small changes in nutritional condition, such as return body mass, return rate and reproductive success. To address this issue, we equipped 34 common murres Uria aalge and 35 thick-billed murres U. lomvia at 6 colonies in the eastern Canadian Arctic and sub- Arctic with geolocators for 1 yr and measured baseline corticosterone levels (4 colonies) and body mass (6 colonies) upon device retrieval. Across all colonies, birds equipped with geolocators averaged higher levels of corticosterone and lower body mass than controls, although there were substantial differences among colonies. De spite effects of the devices on corticosterone and body mass, survival (90%) in equipped birds was no different than in control birds at the one colony where long-term resighting data were available, and chick feeding rates were also similar between equipped and un - equipped birds. We suggest that even very small devices can cause chronic stress when applied over long periods, at least for a diving bird with a very high wing loading, but effects on birds in the present study were not sufficiently pronounced to influence adult survival or chick provisioning rates.