Contrasting strategies of provisioning and chick growth in two sympatrically breeding albatrosses at Campbell Island, New zealand

The provisioning strategies of two closely related species of albatross bre eding sympatrically were studied at Campbell island, New Zealand. Black-bro wed Albatrosses (Diomedea melanophrys) had a higher provisioning rate of ch icks than Grey-headed Albatrosses (D. chrysostoma) as a result of a higher feeding frequency. Provisioning and satellite-tracking data suggest that Bl ack-browed Albatrosses forage over neritic waters in trips of up to 5 days, in combination with longer trips over oceanic waters. In contrast, it was not possible to separate clearly short and long trips in Grey-headed Albatr osses, but they probably forage mostly over oceanic waters, combined with r afting or feeding near the colony during stays of short duration at sea. No inter-annual differences in foraging trip duration were apparent between y ears for either species. Chicks were fed larger meals at older ages and whe n in poorer condition, probably due to a limitation on the rate of assimila tion of food. For both species, chick condition after feeding did not influ ence the duration of foraging trips. Black-browed Albatrosses from Campbell Island feed locally in neritic waters and up to 2,000 km from the colony, in contrast to conspecifics from other sites which feed principally over ne ritic waters. Grey-headed Albatrosses were largely dependent on oceanic res ources as for conspecifics studied elsewhere. This study shows that foragin g and provisioning strategies are flexible within species, allowing them to exploit more or less distant resources.