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RESEARCH ARTICLE
Contents Vol 107(3)

Using biometric measurements to determine gender of Flesh-footed Shearwaters, and their application as a tool in long-line by-catch management and ecological field studies

Sam Thalmann A E , G. Barry Baker B , Mark Hindell A , Michael C. Double C and Rosemary Gales D
+ Author Affiliations
- Author Affiliations

A Antarctic Wildlife Research Unit, School of Zoology, University of Tasmania, GPO Box 252-05, Hobart, Tas. 7001, Australia.

B Australian Government Antarctic Division, Channel Highway, Kingston, Tas. 7050, Australia. Present address: Institute of Antarctic Southern Ocean Studies, University of Tasmania, Private Bag 77, Hobart, Tas. 7007, Australia.

C Australian Centre for Applied Marine Mammal Science, Southern Ocean Ecosystems, Australian Government Antarctic Division, 203 Channel Highway, Kingston, Tas. 7050, Australia.

D Department of Primary Industries and Water, Box 44, Hobart, Tas. 7000, Australia.

E Corresponding author. Email: sam.thalmann@dpiw.tas.gov.au

Emu 107(3) 231-238 https://doi.org/10.1071/MU07002
Submitted: 10 January 2007  Accepted: 27 July 2007   Published: 7 September 2007

Abstract

We examined sexual dimorphism in 11 morphological characters of the Flesh-footed Shearwater (Puffinus carneipes) and used these characters in a discriminant function analysis (DFA) to enable sexual classification in the field. We also used molecular techniques to determine gender in live birds. Sexual dimorphism was present in all characters tested, with males (n = 50) significantly larger than females (n = 52) in all cases. A stepwise DFA of the 11 morphological characters resulted in gender being correctly assigned in 91% of birds using head–bill length (HBL), minimum bill-depth (MBD), and superior unguicorn-width (SUW), using the generalised function –48.360 + (0.661 × SUW) + (0.931 × MBD) + (0.334 × HBL). Of the nine misclassifications, seven were a result of females being incorrectly assigned as males, indicating an overlap between the upper cut off value for females with the lower threshold value for males. We applied the DFA to an existing morphometric dataset (n = 219) of Flesh-footed Shearwaters caught as incidental by-catch from long-line fishing in the Eastern Tuna and Billfish Fishery. The generalised discriminant function derived from live birds performed poorly when applied to the by-catch sample (only 68.5% correctly sexed), and the issues of data consistency and the application of discriminant functions between populations are discussed. A two-character DFA constructed from the by-catch dataset (–30.128 + 0.206 × HBL + 0.848 × MBD) resulted in 86% of by-catch birds being correctly sexed. The findings suggest that a combination of the morphological traits HBL, MBD and SUW are sufficiently robust to use in the field to determine the gender of live birds. The merits and application of this technique are discussed in relation to seabird conservation and management.


Acknowledgements

This study was supported through funding from the Australian Department of Environment and Heritage. Special thanks go to Mary-Anne Lea for valuable assistance in the field. David Priddel and Nicholas Carlile from New South Wales National Parks and Wildlife provided valuable input, direction and field assistance. Project support from the Lord Howe Island Board facilitated fieldwork at the study site. Animal ethics approval for the study was given by the University of Tasmania, and the study was conducted under permit from the NSW National Parks and Wildlife Service. Tasmanian DPIW staffs are gratefully acknowledged for assistance in morphometric data collection from the by-catch birds. Two anonymous reviewers provided valuable comments on a previous version of this manuscript.


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