Obligate use of feeding territories by breeding New Zealand fairy terns (Sternula nereis davisae)

The use of defended feeding territories by New Zealand fairy terns (Sternula nereis davisae) during the breeding season was investigated using 11 years of observations of individually colour-banded birds on Mangawhai Harbour. Breeding birds occupied discrete, spatially fixed feeding territories that were actively defended and used exclusively. Birds without feeding territories did not breed. Territory establishment began about 4 months before laying and was closely integrated with courtship, extending the breeding season without increasing time available for nesting. Males often retained the same feeding territory from year to year, delaying the recruitment of younger males into the breeding population and slowing population growth despite high survival to adulthood. Fierce defence of feeding territories suggests that there is potential competition for food.