Diving Ability of Blue Petrels and Thin-Billed Prions

Abstract

Capillary depth recorders (Burger and Wilson 1988) are useful tools for studying the foraging ecology of seabirds, and have been used successfully on penguins, alcids, shags and gannets (Burger 1991, Wanless et al. 1991, Adams and Walter 1993, Croxall et al. 1993). Recent studies of Procellariiformes have revealed that diving petrels (Pelecanoides georgicus and P. urinatrix) are able to dive routinely down to 25-40 m (Prince and Jones 1992, Chastel 1994). Furthermore, investigations on albatrosses (Prince et al. 1994), and on the White-chinned Petrel Procellaria aequinoctialis (Huin 1994), have shown that these seabirds can reach a depth of several meters, giving a new insight on the foraging techniques of albatrosses and petrels, which are generally regarded as surface-seizers (Harper 1987, Prince and Morgan 1987). The Blue Petrel Halobaena caerulea and the Thinbilled Prion Pachyptila belcheri are small burrow-nesting petrels (190 and 150 g, respectively). At Kerguelen Islands these two seabirds breed in very large numbers (up to 1 million pairs, Weimerskirch et al. 1989); the prions particularly are believed to have a significant impact on subantarctic resources (Ridoux 1994). During the chick-rearing period (50 days, Weimerskirch et al. 1994), both species alternate long and short foraging trips over pelagic and neritic waters (Weimerskirch et al. 1994) and prey mainly on small crustaceans (Harper 1972, Prince 1980, Ridoux 1994), principally by surface-seizing (Harper 1987, Prince and Morgan 1987). This paper reports the first study on maximum dive depths attained by Blue Petrels and Thin-billed Prions, during the chick-rearing period at Kerguelen Islands.