Sex determination of Dupont's lark Chersophilus duponti using molecular sexing and discriminant functions

Authors: Matthias VÖGELI, David SERRANO, José L. TELLA, María MÉNDEZ and José A. GODOY

E-mail: matthias@ebd.csic.es

Published: Volume 54(1), June 2007. Pages 69-79.

Language: English

Keywords: sexual size dimorphism, biometry, discriminant function analysis, molecular sexing, Dupont´s lark and Chersophilus duponti

Summary:

Aims: To test for sexual size dimorphism in external measurements of the Dupont's lark Chersophilus duponti, using a sample of live birds previously sexed by molecular techniques, and to obtain discriminant functions to easily sex birds in hand.

Location: Birds were captured in different populations throughout Spain and Morocco. Most birds were trapped in the Ebro Valley (north-eastern Spain).

Methods: A total of 317 adult and 42 yearlings were captured, banded, weighted and measured. A drop of blood was extracted for molecular sexing. After testing for sex differences in body size, discriminant function analyses were performed to identify the best traits for sexing both juveniles and adults.

Results: All the measured parameters differed significantly between sexes in adult Dupont's larks. The best discriminant function accurately assigned sex to 99.0 % of the adults. The parameter which gave the best single factor correlation with sex was wing length, and the discriminant function with only this variable classified correctly 97.5 % of all the adults. An adult would be a male if wing length > 97 mm and a female if wing length < 97 mm. Sex had a significant effect on all parameters of juvenile individuals as well, except for bill depth. The best discriminant function, using wing length and cranium size, predicted correctly the sex of 97.6 % of the juveniles.

Conclusions: Dupont's lark showed clear size dimorphism, males being heavier and larger than females in nearly all measured traits. From an evolutionary perspective, this difference could be explained by processes of intra- and inter-sexual competition, and even by potential costs linked to song flight in males. In any case, the discriminant functions produced using morphometry of individuals previously sexed by molecular procedures provided a highly accurate, inexpensive and fast method for sexing this threatened species in hand, which can help to interpret and understand many questions about its behavioural and population ecology.

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