Aspects of the breeding biology of the Black shag (Phalacrocorax carbo, novaehollandiae) at Pencarrow, Wellington, with special reference to diet : a thesis in partial fulfilment of the requirements for the degree of Masters of Science in Zoology at Massey University
Aspects of the breeding biology, diet and movements of Black shags (Phalacrocorax carbo novaehollandiae) were studied at Pencarrow Colony. Lake Kohangatera. Wellington. The breeding behaviour of adult birds did not differ from that described in overseas research. Both parents were involved in all aspects of incubation and rearing young, but males collected material for the nest, and females remained at the nest site to build the nest, often with the assistance of the males. Agonistic behaviour was most often shown in the defense of the nest site and mostly involved warning than direct attack. Inter-bird competition within the colony most often involved the displacement of roosting birds by birds returning to the colony. Eighteen pairs were successful in laying eggs and a total of 39 chicks hatched. For the broods that survived to Hedge one had 1 chick, nine had 2. and one had three young. Breeding success, as measured by the number (2.1 ±0.1) of fledged young per nest, was higher than that recorded (Powlesland & Reese 1999) between 1993-98. However the rate of nest failure was twice as high. The variation in breeding success observed at the Pencarrow colony also occurs in Black shag populations in other counties. Black shags at Pencarrow colony are primarily marine foragers. Only one instance of freshwater foraging was identified in 1999. Half of the diet identified in regurgitated pellets comprised one fish species. Wrasse (spotty). Twenty-two different prey items were found in the 121 pellets recovered from the ground underneath the colony. Fish are the predominant prey with 17 different specics confirmed. There was no significant difference (p > 0.1) in the number of prey items per pellet over the eight months they were collected. Movements of adults and fledged young appear to be partially dispersive. The continued presence and return of birds banded since 1990 also suggests a sedentary core population at the colony. The daily presence of adults engaged in foraging activities along the eastern side of Wellington harbour suggests that this area is the preferred foraging area during the breeding season. The number of adult Black shags seen throughout the year in marine areas was significantly higher than in freshwater areas. Young birds did not permanently disperse away from the colony immediately after fledging but returned to the colony to roost overnight. Their most preferred daytime roost in the first few months after fledging was the Mai Mai on Lake Kohangatera 1 km from the colony. The first fledged bird seen roosting overnight away from the colony was on 1 January 2000 (c. 7 months and 2 weeks old).