Crepuscular foraging by a pursuit-diving seabird: tactics of common murres in response to the diel vertical migration of capelin

The spatial and temporal distribution of prey directly influences the foraging and feeding behaviour of predators. To investigate predator–prey interactions through the diel cycle, we examined continuous records of diving activity by a pursuit-diving seabird, the common murreUria aalge, in conjunction with fine-scale data on the vertical distribution of their main prey, capelinMallotus villosus, off the northeast Newfoundland coast, Canada. Diurnal patterns in the diving activities of murres closely reflected changes in the vertical distribution and movements of capelin. During daylight hours, 43% of murre dives were deep (≥50 m), bringing murres into sub-0°C water in the Cold Intermediate Layer (CIL; ~40 to 240 m), when 82% of capelin biomass was located within or below the CIL. At night, murres concentrated diving activity at shallower depths (94% of dives were