Foraging strategies of grey-headed albatrosses Thalassarche chrysostoma: integration of movements, activity and feeding events

Abstract

We identified a range of foraging strategies adopted by grey-headed albatrosses Thalassarche chrysostoma rearing chicks at Bird Island, South Georgia, by simultaneously using satellite telemetry, wet/dry activity recorders and stomach temperature loggers. The albatrosses foraged mostly over oceanic waters, probably associated with the Polar Front north of South Georgia, and also over shelf-slope waters around the Antarctic Peninsula. After leaving the colony, birds commuted to areas with predictable prey concentrations, where they remained for several days. During search periods, birds landed more often and had a higher intake rate, but spent the same proportion of time in flight as on commuting days. Although intake rates were particularly high in shelf-break waters around the Antarctic Peninsula (only one individual foraged in this area), prey were also consumed in reasonable quantities during commuting flights. While at sea, birds spent most (81%) of the day flying, and most (94%) of the night resting on the water. A considerable proportion (26% by mass) of prey was consumed during darkness. The majority of prey were detected and captured during search flights, but 35% were located while sitting on the sea surface. Many ingestion events (up to 27% of the overall food intake) showed temperature signatures characteristic of fluids, suggesting that albatrosses may feed on gelatinous and rapidly digested prey (e.g. salps and jellyfish) much more often than previously suspected. Diet samples delivered to the chicks comprised mostly squid (particularly Martialia hyadesi) and Antarctic krill Euphausia superba.

Tracking Cairns: Biologging Improves the Use of Seabirds as Sentinels of the Sea

“…Although several studies found correlations between the distribution of birds and prey (Catry et al, 2004;Weimerskirch et al, 2005;Fauchald and Tveraa, 2006), one study found no relationship between foraging effort and fish stocks (Croll et al, 2006), or only with primary productivity, rather than fish stocks (Grémillet et al, 2008). Thus, species may vary in their responses to food supply in both colonybased reproductive parameters, and biologger-derived foraging parameters.…”

Either taking it easy or feeling too tired: old Cory’s Shearwaters display reduced activity levels while at sea

“…1 Box-plots depicting the number of take-offs and landings (per day or night) of Old (N = 18) and Mid-aged (N = 17) Cory's Shearwaters Calonectris diomedea. Differences were tested on logtransformed data (see Table 1 for statistics) 7.5 9.0 M-W U = 100.5 Ornithol (2011) 152:549-555 553 active during the latter (Catry et al 2004;Phalan et al 2007; this study). The disproportionate reduction of activity among old Shearwaters during darkness might reflect a strategy to avoid demanding activities when they are less likely to yield a benefit, given that foraging at night seems to be less profitable for visual predators such as seabirds (Catry et al 2004).…”

“…Differences were tested on logtransformed data (see Table 1 for statistics) 7.5 9.0 M-W U = 100.5 Ornithol (2011) 152:549-555 553 active during the latter (Catry et al 2004;Phalan et al 2007; this study). The disproportionate reduction of activity among old Shearwaters during darkness might reflect a strategy to avoid demanding activities when they are less likely to yield a benefit, given that foraging at night seems to be less profitable for visual predators such as seabirds (Catry et al 2004). An experimental study with Cory's Shearwaters showed that handicapped birds (carrying extra mass) also reduced their activity levels (less time spent flying) during darkness (Passos et al 2010).…”

Are deep-sea cephalopods really common preys for oceanic seabirds?

“…Cephalopods are also known as the main prey item for several pelagic predators such as tunas, billfishes, oceanic sharks and cetaceans, which reflect the abundance of cephalopods in the epi and mesopelagic environments. However, how albatrosses locate and catch cephalopods is still subject of much debate (Croxall & Prince 1994, Catry et al 2004, Weimerskirch et al 2005). …”

“…Moreover, ommastrephids are abundant at the sea surface only at night (Roper & Young 1975). Grey-headed spent 86 -94% of their nighttime sitting on the sea, once diving is chiefly limited by their visual acuity (Huin & Prince 1997, Catry et al 2004.…”