MEPS 501:279-290 (2014)  -  DOI: https://doi.org/10.3354/meps10696

ABSTRACT: Diving behaviour of seabirds has been studied using data logging devices, but little is known about underwater predator–prey interactions during dives. We used stationary video cameras to investigate how the underwater foraging behaviour of common murres Uria aalge was influenced by the density and behaviour of their main prey fish, capelin Mallotus villosus, at spawning sites on the northeast Newfoundland coast during July, 2009-2012. From ~720 h of video, we analyzed 99 events where capelin and murres were observed together, ranging from 1-20 s, and 952 events where murres were observed alone, ranging from 1-14 s. Although 91% of all video footage of capelin was in high density schools, 69% of active foraging behaviour of murres (i.e. attempted contacts, approaches) was exhibited on individual capelin, compared to 24% on low density shoals and 7% on high density schools. Similarly, more murres were observed turning, a proxy of area-restricted search behaviour, when solitary and low density capelin shoals persisted for longer durations relative to when schools persisted for longer. When murres made contact with capelin (n = 16), ~70% (n = 11) were deemed successful (i.e. resulted in ingestion or ascent with fish in bill). Unsuccessful contacts resulted from fish escaping during beak manipulations to orient the fish head-first. Capelin were 7-11 times more likely to accelerate when murres displayed active versus passive (i.e. search, travel) foraging behaviours and 5-6 times more likely to accelerate in response to murre presence when in schools relative to low density shoals or solitary individuals. Overall, these results suggest that murres may increase their foraging success within areas of high prey density by preferentially searching for and targeting solitary fish that are less responsive to predators.

KEY WORDS: Seabird · Common murre · Capelin · Foraging behaviour · Schooling · Antipredator · Predator–prey