Working the day or the night shift? Foraging schedules of Cory’s shearwaters vary according to marine habitat

Abstract

The diel vertical migration of zooplankton and many other organisms is likely to affect the foraging behaviour of marine predators. Among these, shallow divers, such as many seabirds, are particularly constrained by the surface availability of prey items. We analysed the atsea activity of a surface predator of epipelagic and mesopelagic prey, Cory's shearwater Calonectris diomedea, on its several wintering areas (spread throughout the temperate Atlantic Ocean and the Agulhas Current). Individual shearwaters were mainly diurnal when wintering in warmer and shallower waters of the Benguela, Agulhas and Brazilian Currents, and comparatively more nocturnal in colder and deeper waters of the Central South Atlantic and the Northwest Atlantic. Nocturnality also correlated positively with bathymetry and negatively with sea-surface temperature within a single wintering area. This is possibly related to the relative availability of epipelagic and mesopelagic prey in different oceanic sectors, and constitutes the first evidence of such flexibility in the daily routines of a top marine predator across broad spatial scales, with clear expression at population and individual levels.

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

“…Mackley et al 2010), Murphy's petrels increase their flight activity at dawn, suggesting that they are predominantly crepuscular and diurnal rather than nocturnal foragers (contra Imber et al 1995). The tracked birds consistently began to fly more in the hour or 2 before sunrise (except during incubation when their flight activity was always high), consistent with the hypothesis that they and other subtropical and tropical species rely heavily on nocturnally migrating prey, such as mesopelagic fish and squid (Ashmole 1971, Imber et al 1995, Dias et al 2012. Foraging by petrels is likely to be restricted by darkness, and morning twilight provides an optimal window when prey are still accessible and there is sufficient light for their visual detection.…”

Seabirds and demersal longliners in the northwestern Mediterranean: factors driving their interactions and bycatch rates

“…Belda & Sánchez 2001, Laneri et al 2010. This is because seabird species in the Mediterranean are mainly diurnal and are particularly active at dawn and dusk (Passos et al 2010, Dias et al 2012, Meier et al 2015. Concordantly, incidental catches were most frequent at dawn, although catches can also be high during daytime.…”

Individual variability in the migratory path and stopovers of a long-distance pelagic migrant

“…In fact, their behavioural flexibility (also expressed in other traits of the migratory behaviour; Dias et al 2011Dias et al , 2012b can be regarded as an adaptive advantage in the context of humaninduced changes in marine ecosystems (Grémillet & Boulinier 2009). However, the variability in the location of their stopovers and paths, at least in some parts of the routes and at a medium scale (tens to a few hundreds of kilometres), poses relevant challenges in the definitions of marine protected areas or of conservation corridors for marine migrants (Block et al 2011;Camphuysen et al 2012).…”