Preliminary investigation of the costs of incubation in the Australasian Gannet (Morus serrator) breeding in Port Phillip Bay, Victoria
A. D. Ewing A , F. I. Norman B , S. J. Ward A and A. Bunce CA Department of Zoology, University of Melbourne, Parkville, Vic. 3052, Australia.
B Arthur Rylah Institute for Environmental Research, Department of Sustainability and Environment, PO Box 137, Heidelberg, Vic. 3084, Australia.
C School of Ecology and Environment, Deakin University, 221 Burwood Highway, Burwood, Vic. 3125, Australia.
D Corresponding author. Email: a.ewing@zoology.unimelb.edu.au
Emu 105(2) 137-144 https://doi.org/10.1071/MU03061
Submitted: 18 December 2003 Accepted: 4 April 2005 Published: 30 June 2005
Abstract
To optimise lifetime reproductive success, individuals must balance current reproductive effort against future reproductive prospects. In birds, incubation and chick-rearing must involve costs, and manipulation of the length of incubation offers an insight into some costs affecting adults. An experiment was conducted at a colony of Australasian Gannets in Port Phillip Bay, Victoria, in which length of incubation was manipulated so that some adults experienced short (10–20 days duration), long (70–80 days) or normal (~45 days) incubation periods. Adults with a manipulated incubation period did not show significant differences in weight change (taken here to reflect cost) during incubation or chick-rearing compared with controls. Manipulation of length of incubation did not significantly affect the hatching success or the growth rate of chicks involved and is not, therefore considered to impose an increased reproductive cost. This suggests that the Australasian Gannet has the capacity to maintain body condition and successfully rear young despite modified duration of incubation.
Acknowledgments
We thank Kath Handasyde and Graham Coulson (Department of Zoology, University of Melbourne) for their quite varied and unique assistance during this study. Boat transport to and from the study site was provided routinely by Rod Watson of Queenscliff Marine Station, although staff of Parks Victoria, Queenscliff, also helped out on occasion. Christopher Robertson (Wellington, New Zealand) provided enthusiasm and a novel weighing technique, and a host of volunteers assisted in various ways throughout the project. Rob Day, Mick Keough (Department of Zoology, University of Melbourne) and Michael Scroggie (Arthur Rylah Institute) assisted with statistical analyses. This investigation on Australasian Gannets at Popes Eye Marine Reserve was conducted under permits issued by the University of Melbourne Animal Experimentation Ethics Sub-Committee (Register number 01064) and the Department of Natural Resources and Environment (Permit number 10001510).
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