Use of geolocators for investigating breeding ecology of a rock crevice-nesting seabird: method validation and impact assessment

1: Investigating ecology of marine animals, imposes a continuous challenge
due to their temporal and/or spatial unavailability. Light-based
geolocators (GLS) are animal-borne devices that provide relatively cheap
and efficient method to track seabird movement and are commonly used to
study migration. Here we explore the potential of GLS data to establish
individual behaviour during the breeding period in a rock crevice-nesting
seabird, the Little Auk, Alle alle. 2: By deploying GLS on 12 breeding
pairs, we developed a methodological workflow to extract birds’ behaviour
from GLS data (nest attendance, colony attendance and foraging activity),
and validated its accuracy using behaviour extracted from a
well-established method based on video recordings. We also compared
breeding outcome, as well as behavioural patterns of logged individuals
with a control group treated similarly in all aspects except for the
deployment of a logger, to assess short-term logger effects on fitness and
behaviour. 3: We found a high accuracy of GLS-established behavioural
patterns, especially during the incubation and early chick rearing period
(when birds spend relatively long time in the nest). We observed no
apparent effect of logger deployment on breeding outcome of logged pairs,
but recorded some behavioural changes in logged individuals (longer
incubation bouts and shorter foraging trips). 4: Our study provides a
useful framework for establishing behavioural patterns (nest attendance
and foraging) of a crevice-nesting seabird from GLS data (light and
conductivity), especially during incubation and early chick rearing
period. Given that GLS deployment does not seem to affect the breeding
outcome of logged individuals but does affect fine-scale behaviour, our
framework is likely to be applicable to a variety of crevice/burrow
nesting seabirds, even though precautions should be taken to reduce
deployment effect. Finally, because each species may have its own
behavioural and ecological specificity, we recommend performing a pilot
study before implementing the method in a new study system.