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RESEARCH ARTICLE
Contents Vol 109(1)

Biometrics, sexing criteria, age-structure and moult of Sooty Oystercatchers in south-eastern and north-western Australia

Birgita D. Hansen A E , Clive D. T. Minton B , Rosalind Jessop C and Peter Collins D
+ Author Affiliations
- Author Affiliations

A Australian Centre for Biodiversity, School of Biological Sciences, Monash University, Vic. 3800, Australia.

B 165 Dalgetty Road, Beaumaris, Vic. 3193, Australia.

C Phillip Island Nature Park, PO Box 97, Cowes, Vic. 3922, Australia.

D Broome Bird Observatory, PO Box 1313, Broome, WA 6725, Australia.

E Corresponding author. Email: birgita.hansen@sci.monash.edu.au

Emu 109(1) 25-33 https://doi.org/10.1071/MU07045
Submitted: 9 August 2007  Accepted: 11 September 2008   Published: 20 January 2009

Abstract

Since 1980, 856 Sooty Oystercatchers (Haematopus fuliginosus) have been caught and banded in Australia by the Victorian Wader Study Group (n = 801, from southern Australia) and the Australasian Wader Studies Group (n = 55 birds, all from north-western Australia). The biometric data collected were analysed for differences between sexes and ages and for geographical differences. Females were larger than males in all biometric dimensions, in all age-groups and in both geographical regions. For both subspecies – H. f. fuliginosus in south-eastern Australia and H. f. opthalmicus in north-western Australia – length of bill (exposed culmen) was the most discriminating parameter for determination of sex. Weights of adult females increased markedly towards the end of the moulting period. In south-eastern Australia, adult males considerably outnumber adult females in catches. Furthermore, adult males also outnumbered adult females in late autumn–early winter samples; at other times, and in other age-groups, the sex-ratio was more evenly balanced. Differential survival or spatial distribution of females and males are proposed as the mechanisms causing male-biased tertiary sex-ratios in catches. South-eastern Australian birds were larger and heavier than their northern counterparts. Furthermore, comparisons between Sooty Oystercatchers and the sympatric congener, the Australian Pied Oystercatcher (H. longirostris) showed the former to be significantly larger and heavier in both parts of the country.

Additional keywords: Haematopus longirostris, moult-duration, Pied Oystercatcher, sex-ratio.


Acknowledgements

We would like to thank all members of the VWSG and AWSG who volunteered so much effort and time to catching birds. We would like to thank Danny Rogers and two anonymous reviewers for many helpful comments that improved this manuscript. We would also like to thank Ken Rogers for assistance in using the software SHEBA2b, and Les Underhill for kindly providing feather-mass data from his African Black Oystercatcher database for use in the moult analyses. The Australian Bird and Bat Banding Schemes (ABBBS) is thanked for providing bands. We would also like to acknowledge the support provided by Parks Victoria, both with boats and boat drivers, without whom much of this fieldwork could not have occurred. In particular, thanks must go to the landowners for permission to access foreshores. All research with birds was approved by the ABBBS and research permits issued by Department of Sustainability and Environment (Victoria) and Department of Conservation and Land Management (Western Australia).


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