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.

Experiments were carried out on breeding streaked shearwaters (Calonectris leucomelas), mean body mass, 560 ± 52 g, (n = 25) at Funakoshi-Ohshima Island (39'N,141'E), Japan, during the chick-rearing periods of August-September 2018 and August 2019. A total of 27 birds were captured by hand at their burrows and one tag was attached to each bird. 11 individuals were tagged with GPS and acceleration (AxyTrek) tags (Axy-Trek Marine, Technosmart, Guidonia Montecelio, Italy) in 2018 and 9 in 2019. Tags were attached to the back feathers using waterproof tape (Tesa, Hamburg, Germany) and instant glue (Loctite, Dusseldorf, Germany).

Behaviour detections were generated using the method described in the related study. Behaviours were classed as FL (flight), Takeoff, Dive (foraging dives), Take-off bout (surface seizing - see article), and Unknown. Two files are present for each day of AxyTrek recording and are named in the format TagID-YYYYMMDDForageGPS or TagID-YYYYMMDDEthoTransitions. *ForageGPS files contain 4 columns, the datetime values, latitude, longitude, and forage (whether foraging behaviour was detected within 30 seconds of the GPS fix). *EthoTransitions files contain 2 columns, Var1 is the start times of the behaviours identified in column tBeh.

Data were split by day to ease computing of the behaviour detection method, therefore each tag has multiple files that make up the total recording duration.