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

Abstract

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 murre Uria aalge, in conjunction with fine-scale data on the vertical distribution of their main prey, capelin Mallotus 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 < 50 m) when 86% of capelin biomass was in the upper water column. Capelin migrated through the water column during twilight periods, moving up at dusk and down at dawn. In response, murres' diving frequency increased and diving depths were graduated, becoming shallower through dusk and deeper through dawn. Crepuscular habits indicate that capelin are more accessible during twilight periods. In summary, though murres are constrained by commuting costs, they show exceptional behavioural flexibility in their efforts to access capelin throughout their diel vertical migration (DVM). The various trade-offs involved in such predator-prey interactions are discussed, as are the ecological consequences of the DVM pattern across trophic levels.

Telomere length is a strong predictor of foraging behavior in a long‐lived seabird

“…Male murres attend the colony more at night so as to be available to accompany the chick to sea at fledging, which occurs at dusk. Night diving is usually shallower (Regular et al 2010), and females dove more shallowly in our study, yet this difference was not driven by body size. Despite their longer commutes and more nights away from the colony, females did not perform fewer trips than males (Young et al, unpublished manuscript), so their parental investment is quite high.…”

“…For example, days are shorter at lower latitudes in the summer, and at lower latitude colonies we found birds allocating more of their time to diving after sunset. Night diving takes advantage of the diel migration of zooplankton (Regular et al 2010). Night diving may also have been higher on colonies where a night spent at sea provided access to productive prey sources.…”

Escaping the oligotrophic gyre? The year-round movements, foraging behaviour and habitat preferences of Murphy’s petrels

“…The eastern region of the South Pacific Gyre is also used extensively by leatherback turtles Dermochelys coriacea targeting zooplankton such as jellyfish (Saba et al 2008, Shillinger et al 2011. Mesopelagic prey, thought to be a dominant component of food webs in deep, oceanic waters (Ashmole 1971), often perform diel vertical migrations (DVMs) to the sea surface at night (Hays 2003), making them available to air-breathing predators such as turtles and seabirds (Regular et al 2010, Shillinger et al 2011. Analysis of Murphy's petrel diets during chick-rearing has indicated they feed predominantly on bioluminescent squid, emphasizing their reliance on DVM prey (Imber et al 1995).…”

Predictable hydrodynamic conditions explain temporal variations in the density of benthic foraging seabirds in a tidal stream environment

“…Diurnal patterns of foraging activities are typically linked with the behaviour of mobile prey (e.g. diel-vertical migration: Regular et al, 2010), changes in light-levels effecting the detection of prey (Regular et al, 2011), or commuting distances between breeding colonies and foraging areas. However, black guillemots breed locally and probably exploit sessile benthic prey items, whereas light levels would not differ greatly between morning and afternoon periods.…”