GPS tracks and behaviour detection of chick-rearing streaked shearwaters at Funakoshi Oshima Island, Japan, 2018 & 2019

The study of seabird behaviour has largely relied on animal-borne tags to
gather information, requiring interpretation to estimate at-sea
behaviours. Details of shallow-diving birds’ foraging are less known than
deep-diving species due to difficulty in identifying shallow dives from
biologging devices. Development of smaller video loggers allow a direct
view of these birds’ behaviours, at the cost of short battery life.
However, recordings from video loggers combined with relatively low power
usage accelerometers give a means to develop a reliable foraging detection
method. Combined video and acceleration loggers were attached to streaked
shearwaters in Funakoshi-Ohshima Island
(39'N,141'59''E) during the breeding season in 2018.
Video recordings were classified into behaviours and a detection
method was generated from the acceleration signals. Two foraging
behaviours, surface seizing and foraging dives, are reported with video
recordings. Surface seizing was comprised of successive take-offs and
landings (mean duration 0.6 and 1.5s, respectively), while foraging dives
were shallow subsurface dives (1.9s mean duration) from the air and water
surface. Birds were observed foraging close to marine predators, including
dolphins and large fish. Foraging detections were validated against video
recordings (surface seizing true positive 78%, false positive 5%, foraging
dive true positive 66%, false positive <1%). The detection method
was implemented to data from longer duration acceleration and GPS datasets
collected during the 2018 and 2019 breeding seasons. Foraging trips lasted
between 1-8 days, with birds performing on average 16 surface seizing
events and 43 foraging dives per day, comprising <1% of daily
activity, while transit and rest took up 55% and 39%, respectively. This
foraging detection method can address the difficulties of recording
shallow-diving foraging behaviour and provides a means to measure activity
budgets across shallow diving seabird species.