Effects of back‐mounted biologgers on condition, diving and flight performance in a breeding seabird

Biologging devices are providing detailed insights into the behaviour and movement of animals in their natural environments. It is usually assumed that this method of gathering data does not impact on the behaviour observed. However, potential negative effects on birds have rarely been investigated before field‐based studies are initiated. Seabirds which both fly and use pursuit diving may be particularly sensitive to increases in drag and load resulting from carrying biologging devices. We studied chick‐rearing adult common guillemots (Uria aalge) equipped with and without back‐mounted GPS tags over short deployments of a few days. Concurrently guillemots carried small leg‐mounted TDR devices (time‐depth recorders) providing activity data throughout. Changes in body mass and breeding success were followed for device equipped and control guillemots. At the colony level guillemots lost body mass throughout the chick‐rearing period. When‐equipped with the additional GPS tag, the guillemot...