RESIGHTS, RECAPTURES AND RECOVERIES OF AUSTRALASIAN GANNETS Morus serrator BREEDING IN PORT PHILLIP BAY, VICTORIA
| Posted: |
21/07/2021 |
| Author(s): |
F. I. Norman |
Colonies of Australasian Gannet
Morus serrator in Port Phillip Bay, Victoria, started with three nests at Wedge
Light in 1966/1967, and have now expanded both in size and number; there are now about 1 000 gannets breeding
at eight artificial sites in the Bay. Between 1967 and 2000, 1 116 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 five 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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