Sex determination in glossy ibis chicks based on morphological characters

Authors: Jordi FIGUEROLA, Luís GARCIA, Andy J. GREEN, Fernando IBAÑEZ, Manuel MAÑEZ, José Luís DEL VALLE, Héctor GARRIDO, José Luís ARROYO and Rubén RODRÍGUEZ

E-mail: jordi@ebd.csic.es

Published: Volume 53(2), December 2006. Pages 229-235.

Language: English

Keywords: discriminant function, genetic analyses, glossy ibis, leg morphology, sex determination, sexual size dimorphism and Plegadis falcinellus

Summary:

Aims: We derived two discriminant equations to sex glossy ibis Plegadis falcinellus chicks (2 - 5 weeks old) based on morphological characters.

Location: Doñana, South-West Spain.

Methods: Wing length and tarsus length and width of 198 individuals were measured in the 2002 and 2003 breeding seasons.

Results: Tarsus width was the most discriminant character and in combination with wing length allowed us to sex 86.9% of individuals correctly. A formula based on wing and tarsus length also sexed 84.9% of individuals correctly. The reliability of this second equation was also tested with an independent sample of 209 individuals measured in 2004, with error rates similar to those of the original data. Intervals for discriminant scores reducing errors in sexing to 10% or 5% were derived, at the cost of reducing the proportion of individuals that can be sexed. These equations should not be applied in other localities without validation, but our analyses suggest they can be used on different cohorts. We also describe a visual sexing technique found to have 95% accuracy for an experienced observer.

Conclusions: Sex can be reliably determined for many glossy ibis chicks. Given the considerable sexual size dimorphism found in many species of the family Threskionidae, tarsus width is likely to be a good variable to include in future analyses of sexual dimorphism in spoonbills and ibises.

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