Underwater behaviour of common murres foraging on capelin: influences of prey density and antipredator behaviour

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 arearestricted 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.

Dynamic habitat corridors for marine predators; intensive use of a coastal channel by harbour seals is modulated by tidal currents

“…Concentrating foraging efforts at times and locations of increased prey vulnerability has been shown to significantly enhance foraging success of a range of terrestrial and marine predators (Quinn and Cresswell 2004; Hopcraft et al 2005; Crook and Davoren 2014). Narrow channels such as the one in the current study are tidally energetic; strong turbulence provides a potential mechanism to disorient prey and imposes a metabolic cost as prey try to maintain orientation (Zamon 2002; Liao 2007).…”

Riding the tide: use of a moving tidal-stream habitat by harbour porpoises

“…Opportunities for predators may therefore arise from fish being involuntarily displaced or disoriented. Concentrating foraging efforts at times and locations of increased prey vulnerability can significantly enhance predator foraging success (Quinn & Cresswell 2004, Hopcraft et al 2005, Crook & Davoren 2014, and similar mechanisms may operate in tidal-stream habitats. Porpoise presence in tidal streams is likely driven by sitespecific circumstances at small spatiotemporal scales that should be considered when investigating potential interactions with human activities such as marine renewable energy extraction (Inger et al 2009, Shields et al 2011, Jones et al 2014, Scott et al 2014.…”

Relative importance of local enhancement as a search strategy for breeding seabirds: an experimental approach

“…Although pursuit-divers are considered 'initiators' of mixed-species feeding assemblages in other regions (Hoffman et al, 1981), this is unlikely in our study area. Capelin are associated with the sea bed (Davoren et al, 2006), and murres typically attack solitary capelin from above at capelin spawning sites (Crook & Davoren, 2014), thereby likely driving prey deeper in the water column. Gannet diets also include larger pelagic fish (e.g.…”

“…Mixed-species feeding assemblages occur within the region (Davoren, 2007(Davoren, , 2013b, typically as large, stable foraging aggregations of seabirds and whales targeting capelin shoals near the seabed. Unlike other regions, common murres target individual capelin separate from or on the periphery of large shoals and do not drive fish schools to the surface (Crook & Davoren, 2014). Thus, mixed-species feeding assemblages associated with concentrations of near-surface fish in this region are rare.…”