Black-tailed Gull GPS foraging trip data and acceleration raw data

Areas at which seabirds forage intensively can be discriminated by
tracking the individuals’ at-sea movements. However, such tracking data
may not accurately reflect the birds’ exact foraging locations. In
addition to tracking data, gathering information on the dynamic body
acceleration of individual birds may refine inferences on their foraging
activity. Our aim was to classify the foraging behaviors of
surface-feeding seabirds using data on their body acceleration and use
this signal to discriminate areas where they forage intensively.
Accordingly, we recorded the foraging movements and body acceleration data
from seven and ten black-tailed gulls (Larus crassirostris) in 2017 and
2018, respectively, using GPS loggers and accelerometers. By referring to
video footage of flying and foraging individuals, we were able to classify
flying (flapping flight, gliding, and hovering), foraging (surface
plunging, hop plunging, and swimming), and maintenance (drifting,
preening, etc.) behaviors using the speed, body angle, and cycle and
amplitude of body acceleration of the birds. Foraging areas determined
from acceleration data corresponded roughly with sections of low speed and
area-restricted searching (ARS) identified from the GPS tracks. However,
this study suggests that the occurrence of foraging behaviors may be
overestimated based on low-speed trip sections, because birds may exhibit
long periods of reduced movement devoted to maintenance. Opposite, the
ARS-based approach may underestimate foraging behaviors since birds can
forage without conducting an ARS. Therefore, our results show that the
combined use of accelerometers and GPS tracking helps to adequately
determine the important foraging areas of black-tailed gulls. Our approach
may contribute to better discriminate ecologically or biologically
significant areas in marine environments.