Resights, recaptures and recoveries of Australasian Gannets Morus serrator breeding in Port Phillip Bay, Victoria
Colonies of Australiasian Gannet Morus serrator
in Port Phillip Bay, Victoria, started with three nests at Wedge Light in 1966/67, and have now expanded both in size and number; there are now about 1000 Gannets breeding at eight artificial sites in the Bay. Between 1967 and 2000, 1116 gannet chicks were banded at sites in Port Phillip Bay, mostly at Pope's Eye (759) and Wedge Light (354), off Queenscliff. During subsequent studies, mainly at Pope's Eye and from 1988 onwards, band numbers were obtained from adults present at breeding sites as practicable. Resightings (or recaptures) of birds (172) banded as chicks are reviewed in relation to source, age and movement between sites in Port Phillip Bay. Recoveries (birds found dead) of 41 birds banded as chicks (3.7% of those banded) in Port Phillip Bay are discussed with respect to age post banding and location; the occurrence of live birds in rehabilitation centres is also noted. Resights and recaptures at breeding sites in Port Phillip Bay have, essentially, been of birds banded there. Few birds have been resighted from Lawrence Rocks, the major Victorian breeding site, which has itself also expanded (and a new site established on the nearby mainland). Although some may visit nesting colonies earlier, Australasian Gannets in Port Phillip Bay begin breeding at about four years of age and increasingly thereafter. Recoveries to date have been mainly in Port Phillip Bay (56%), often shortly after banding(e.g. 29% within 5 months), but occasional birds have been reported from coastal Tasmania, South Australia and New South Wales. Once recorded as a breeder, usually at natal colonies, birds seldom nested elsewhere; movement between sites generally involved younger, presumably non-breeding gannets. However, although philopatry may be strong, it is affected locally by available space on the artificial platforms. In consequence, as sites are filled, opportunities for younger birds to breed are reduced and the breeding population ages. Annual mortality of breeding adults (of mixed age) is about 6 per cent and, using locally determined breeding success, suggests that the species is capable of producing surplus birds which have expanded some colonies and initiated others. There is little evidence that immigration from distant sites has been responsible for colony growth in Port Phillip Bay, and it appears that local expansion has been internally driven.
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