Exploitation of distant Antarctic waters and close shelf-break waters by white-chinned petrels rearing chicks

Abstract

The foraging ecology of white-chinned petrels Procellaria aequinoctialis rearing chicks was examined at the Crozet Islands in the Southern Ocean, based on satellite tracking, diet and provisioning studies. White-chinned petrels from the Crozet Islands exploit a wide variety of marine environments ranging from sub-tropical waters to the limit of pack-ice at the edge of the Antarctic continent. This capability was made possible by the use of a 2-fold strategy whereby adults exploit alternatively distant oceanic waters and neritic slope waters in the vicinity of the breeding grounds. On average the birds conducted a long foraging trip followed by 2.2 short trips. During trips of long duration over oceanic waters, birds tended to commute mainly to cold, deep Antarctic waters where most foraging activity took place. They commuted from and returned to Crozet at high speeds (mean 31 and 34 km h -1 respectively) with a mean foraging range of 1868 km (maximum 2421 km). In Antarctic waters, the white-chinned petrel appears to feed mainly on pelagic fishes and on Antarctic krill Euphausia superba and concentrates its efforts in waters with sea-surface temperatures of 2°C. During short trips the birds commuted to the Crozet shelf break, where they fed mainly on fish. Diet samples delivered to chicks after short trips indicate that adults relied at least in part on food made available by longliners as baits and discards. Despite its small size compared to albatrosses, the white-chinned petrel from Crozet appears to be a particularly wide-ranging species and an opportunistic feeder in terms of the marine environment exploited, which explains its wide distribution in the Southern Ocean. This study highlights the particular importance of Antarctic waters for this sub-Antarctic species during the chick-rearing period, i.e. in summer when the retreat of the pack-ice makes abundant resources such as Antarctic krill available.