Provenance and sex ratio of Black-browed Albatross, Thalassarche melanophrys, breeding on Campbell Island, New Zealand

Abstract

Small numbers of Black-browed Albatross, Thalassarche melanophrys, breed on Campbell Island, New Zealand. Their dark brown irises had previously been used to distinguish them from the more numerous Campbell Albatross, T. impavida, which has light irises. Blood samples were collected from dark-eyed birds and their partners on Campbell Island to determine their provenance and whether a sex imbalance caused them to breed with Campbell Albatrosses. Analysis of mitochondrial DNA revealed that dark-eyed birds were of three genetically distinct groups: T. melanophrys, Falkland Islands T. melanophrys and T. impavida. The majority of both types of T. melanophrys on Campbell Island were male, hence none was paired with the same taxon, but most of the more widespread form chose dark-eyed mates. Other individuals had a succession of light-eyed partners over several years. Dark-eyed T. impavida may have been hybrid progeny of female T. impavida x male T. melanophrys pairings. One of these birds was banded as a chick in 1970, suggesting that hybridisation has occurred on Campbell Island at least as early as that date. Their presence suggests a low rate of interchange between the island groups or recent immigration of T. melanophrys to Campbell Island and neighbouring island groups.