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RESEARCH ARTICLE
Contents Vol 109(3)

Sexual dimorphism and determination of sex by morphometrics in Blue-fronted Amazons (Amazona aestiva)

Igor Berkunsky A B , Bettina Mahler A and Juan Carlos Reboreda A
+ Author Affiliations
- Author Affiliations

A Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón II Ciudad Universitaria, C1428EGA Buenos Aires, Argentina.

B Corresponding author. Email: igorberkunsky@ege.fcen.uba.ar

Emu 109(3) 192-197 https://doi.org/10.1071/MU08072
Submitted: 19 December 2008  Accepted: 4 May 2009   Published: 13 August 2009

Abstract

On current knowledge, it has not been possible to determine the sex of Blue-fronted Amazons (Amazona aestiva) in the hand, as males and females were thought not to differ in the colour of plumage or size. We used discriminant function analysis to develop equations for determining the sex of Blue-fronted Amazons using in-hand measurements. We took seven measurements of size and one measure of plumage colour (percentage of yellow on the head) from 202 birds in north-western Argentina. The sex of each individual was determined using DNA-based genetic techniques. For all size measurements, males averaged larger than females. Males also had a higher percentage of yellow plumage on the head than females. The percentage of yellow plumage (64%) and body mass (12%) had the highest degree of dimorphism, but also showed high within-sex coefficients of variation, correctly classifying 73% and 72% of the individuals respectively. Although bill-depth had a low degree of dimorphism (7%), it had the lowest coefficient of variation (4%) resulting in the most accurate single-measurement for sexing this species (80% of the individuals). A cross validation process revealed that a discriminant function including three measurements (bill-depth, tibial length and head-width) was more accurate and reliable for determination of sex than single measurements, classifying correctly 85% of the individuals. Our results show that Blue-fronted Amazons are sexually dimorphic for most characteristics of body size and show sexual dichromatism in the colour of the plumage of the head, which allows determination of sex of individuals by morphological variables that can be easily measured in the field.

Additional keywords: Amazona aestiva xanthopteryx, discriminant analysis, sexual dichromatism.


Acknowledgements

We are grateful to R. Ruggera and L. Pagano for partnership and collaboration during fieldwork. Two anonymous reviewers and one member of the editorial board made valuable comments that improved a previous version of this manuscript. I. Berkunsky was supported by fellowships from the Comisión de Investigaciones Científicas de la Provincia de Buenos Aires and Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina (CONICET). J. C. Reboreda and B. Mahler are Research Fellows of CONICET. Our study was partially financed by Parrot People Fundación. This research complies with the current laws of the Argentinean government.


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