Breeding Biology, Diet and Morphometrics of the King Shag, Phalacrocorax Albiventer Purpurascens, at Macquarie Island.

Abstract

Nineteen colonies of the king shag, Phalacrocorax albiventer purpurascens, occur on Macquarie I. varying in size from 3 to 320 breeding pairs. The total population was estimated at 660 breeding pairs in 1975-79. Breeding varied annually, but most eggs were laid in the last half of October with an average clutch size over two seasons of 2.7 eggs. Most chicks hatched by late December and fledged from late January onwards. Minimum age at first breeding was 2 years but most shags did not breed until the age of 4 years or more. Faithful breeding pairs tended to be more successful than those that changed mates although most remained together for only one or two seasons. Male shags had a stronger tendency to retain their nest-site than did females, and it was the female that was responsible for the breakdown of the pair-bond. This breakdown and annual variation in breeding success was thought to be mainly due to shortage of food, which consisted solely of benthic fish.