Kleptoparasitism by Brown Skuas on Albatrosses and Giant-Petrels in the Indian Ocean

Abstract

The behavior of skuas and jaegers (subfamily Stercorarinae) when kleptoparasitizing other seabirds has been studied in detail at breeding colonies (Furness 1987a, b; Maxson and Bernstein 1982; Le Corre and Jouventin 1997), at a coastal estuary along a migration route in Britain (Taylor 1979), in boundary currents off Peru and south Africa (Duffy 1982), and in pelagic waters of the Eastern Tropical Pacific (Spear and Ainley 1993). The size of the host is usually smaller than that of the kleptoparasite. Indeed, only 9 of the 40 host species recorded had a mean body mass greater than that of the parasite (mean body mass of the host was 1.1 to 2.4 times greater than that of the kleptoparasite; Table 1). Attacks by skuas on giant-petrels and albatrosses have not been described. Therefore, we were surprised to see attempted kleptoparasitism by Brown Skuas (form from the Crozet and Kerguelen archipelagoes = Catharacta antarctica lonnbergi sensu Devillers 1978, Malling-Olsen and Larsson 1997; but see Peter et al. 1994) on a Wandering Albatross (Diomedea exulans) and a Northern Giant-Petrel (Macronectes halli), because these hosts are 5.9 and 2.6 times larger, respectively, than the skuas (Table 1). We also report an attempted kleptoparasitism by a Brown Skua on a Light-mantled Albatross (Phoebetria palpebrata) in the Kerguelen Archipelago, and four attempts by Brown Skuas (the Amsterdam Island [Indian Ocean] form, which is similar in size to the Tristan Brown Skua [C. a. hamiltoni]) on Yellow-nosed Albatrosses (Thalassarche chlororhynchos bassi) adjacent to the primary breeding colony of the latter at Amsterdam Island. The kleptoparasitism attempts on the Wandering Albatross and Northern Giant-Petrel were observed while we surveyed seabirds from the R / V Marion Dufrense in the southwestern Indian Ocean. The incident involving the albatross happened on 9 November 1997 at 44?09'S, 51?26'E (238 km from the Crozet Islands), and that involving the giant-petrel occurred on 14 November 1997 at 49?21'S, 66?43'E (147 km from the Kerguelen Islands). LBS, CSO, and SNGH saw both attempts from the flying bridge; DL saw the first attempt from the bridge. The Brown Skua that attacked the albatross was in