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 guillemots lost
mass at close to twice the rate they did when equipped with only the
smaller leg‐mounted TDR device. The elevated mass loss suggests an impact
on energy expenditure or foraging performance. When equipped with GPS tags
diving performance, time‐activity budgets, and daily patterns of activity
were unchanged, yet dive depth distributions differed. We review studies
of tag‐effects in guillemots (Uria spp.) finding elevated mass
loss and reduced chick‐provisioning to be the most commonly observed
effects. Less information is available for behavioural measures, and
results vary between studies. In general, small tags deployed over several
days appear to have small or no measurable effect on the behavioural
variables commonly observed in most guillemot tagging studies. However,
there may still be impacts on fitness via physiological effects and/or
reduced chick‐provisioning, while more detailed measures of behaviour
(e.g. using accelerometery) may reveal effects on diving and flight
performance.