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1 June 2008 Sex Determination for the Great Egret and White Ibis
Garth Herring, Dale E. Gawlik, James M. Beerens
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Most species of wading birds are monomorphic and present few or no external characteristics to allow for sex determination in the field. We used standard morphometric measurements and discriminant function analysis to determine the sex of Great Egrets (Ardea alba) and White Ibises (Eudocimus albus). The models were validated based on sex determination from DNA. Two functions were created for Great Egrets; mass reliably discriminated 88% of our samples, while wing chord separated 81% of our samples. We included mass in the discriminant function analysis for Great Egrets because mass did not vary between years or within our pre-breeding sampling period. Mass was not included in our analysis of White Ibis because it differed by year and within our pre-breeding sampling period. White Ibis samples were separated by a discriminant function using the length of curved bill and tarsus. This function correctly classified 78% of our samples. We provide simplified linear equations to calculate the sex of Great Egrets and White Ibises as well as cut off points where the probability of correctly sexing individuals drops below 75%. Our model can be used to reduce the costs of sex determination by allowing researchers to use expensive DNA analysis techniques only for those individuals that cannot be reliably classified using the simple statistical model.

Garth Herring, Dale E. Gawlik, and James M. Beerens "Sex Determination for the Great Egret and White Ibis," Waterbirds 31(2), 298-303, (1 June 2008).[298:SDFTGE]2.0.CO;2
Received: 16 July 2007; Accepted: 1 December 2007; Published: 1 June 2008
Ardea alba
discriminant function analysis
Eudocimus albus
Great Egret
sex determination
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