Diving behaviour of benthic feeding Black Guillemots
Shoji A., Elliott KH., Greenwood JG., McClean L., Leonard K., Perrins CM., Fayet A., Guilford T.
© 2015 British Trust for Ornithology. Capsule: Dive behaviour in Black Guillemots Cepphus grylle was close to that predicted for a benthic forager by allometry based on body mass. Aims: To report the diving behaviour of Black Guillemots in Northern Ireland. Methods: A time-depth-recorders and GPS logger were deployed on four chick-rearing breeding Black Guillemots. Results: Dive shape implied most dives were benthic with a small number at the start of each bout associated with searching. Diving only occurred during daylight hours, but dive depth was unrelated to light availability outside of the twilight periods. Dive durations (max = 90s; mean = 54s) were shorter and dive depths (max = 15m; mean = 9m) were shallower than recorded for guillemots elsewhere. The birds dived a maximum of 1.8km from the colony. Conclusions: Black Guillemots' dive duration was similar to the value predicted from allometry, and is therefore likely representative of this species. Bathymetry likely influences the dive behaviour of this benthic-feeding species because most dives were U-shaped and dive depths were shallow, which is typical for the relatively shallow water where the birds were observed foraging.