Factors influencing the breeding success of Cape Gannets Morus capensis at Malgas Island in 2002/2003

Abstract

In the 2002/2003 breeding season at Malgas Island, South Africa, 125 nests of Cape Gannets Morus capensis, of which at least one partner was of known age, were monitored. The age of birds at these nests ranged from five to 22 years. At five nests, the ages of both partners were known; ages were similar for birds younger than 10 years but dissimilar for older birds, suggesting Cape Gannets initially choose partners of a similar age but may replace lost partners with younger birds. First clutches, all consisting of one egg, were mainly laid in late September (estimated laying dates 15 August to 1 November). Of first clutches, 61% failed. Relaying took place at 11% of failed nests. Overall, pairs successfully fledged chicks at 43% of nests; no pair fledged two chicks. Breeding success was positively related to the distance of the nest from the edge of the colony, but tended to decrease as age increased. Height of nest and date of laying did not influence breeding success. Older birds bred earlier and further from the edge of the colony than did younger birds.

Ostrich 2008, 79(1): 67–72