Search Strategies of a Pursuit-Diving Marine Bird and the Persistence of Prey Patches

Abstract

Abstract. We explored foraging strategies used by marine animals to search for prey by examining the relative importance of information exchange and memory in a cold ocean environment from 1998 to 2000. Recent technological advances have increased our knowledge of the foraging patterns of marine predators, but few of these studies have concurrently measured prey distribution and behavior. We quantified the arrival and departure behavior of a pursuit-diving, colonial seabird, the Common Murre, Uria aalge, at two colonies on the eastern Newfoundland Shelf through observational techniques. We also measured the distribution, abundance, and behavior of the capelin, Mallotus villosus, the main prey species of murres, within foraging ranges of each colony, using hydroacoustic, vessel-based techniques. Return and departure flight directions of murres did not match at either colony during the same period. This indicated that murres departing colonies did not use information on prey distributions outside of visual range of the colony provided by the flight paths of returning flocks of birds to the colony carrying fish. High-abundance aggregations of capelin were reliably found within specific 2.25-km areas (''hot spots'') for up to two weeks within the foraging ranges of murres from both colonies (ϳ100 km). This circumstance suggests that murres could use memory to locate hot spots on the coarse scale (1-100 km) of foraging ranges from both colonies. Specific commuting routes (regular flight paths) of murres toward and away from hot spots were obvious at sea, and feeding murres consistently marked the location of capelin schools within hot spots. These distributions provided excellent conditions for murres to locate capelin schools on both coarse and fine (1-1000 m) scales by cueing to the activities of conspecifics, known as local enhancement. While central-place foraging from breeding colonies, murres likely use a mixture of memory and local enhancement to locate prey, depending on the spatial and temporal resolution of search and current prey conditions. Uncovering such behavioral mechanisms responsible for predator-prey interactions increases our understanding of linkages among trophic levels and, ultimately, ecosystem dynamics.

Long‐term individual foraging site fidelity—why some gannets don't change their spots

“…This assumption 545 appears valid in some low latitude breeders which forage in oceanic waters (Weimerskirch 2007, 546 Weimerskirch et al 2010). However, in temperate, polar and neritic habitats prey patches may be 547 less variable, perhaps persisting across years (Davoren et al 2003). In accordance with the 548 WSLS hypothesis, we found that spatial consistency in gannets was not absolute (population 549 mean < 0.6; Fig.…”

Ocean control of the breeding regime of the sooty tern in the southwest Indian Ocean

“…In the case of Lys Island, where the availability of prey may be hard to predict, colonialism may increase the breeding success of individuals. However, recent results do not support the information centre hypothesis (Davoren et al 2003). It has even been demonstrated that the size of the colony is negatively correlated to the foraging activity of individuals (Lewis et al 2001, Ainley et al 2003.…”

Temporal shifts in seabird populations and spatial coherence with prey in the southeastern Bering Sea

“…Other factors that affect the coherence of predators and prey include prey abundance (Skov et al 2000, Davoren & Montevecchi 2003, Vlietstra 2005) and the spatial resolution of predator−prey integration (Schneider & Piatt 1986, Mehlum et al 1999, Fauchald et al 2000. Seabirds and prey can be more tightly coupled when prey and seabird abundance is relatively high (Mehlum et al 1999, Fauchald et al 2000, although exceptions do exist, i.e.…”