Sexual dimorphism and sexual determination by morphometric measurements in Blue-fronted Amazons (Amazona aestiva)

BERKUNSKY, I.; MAHLER, B.; REBOREDA, J. C.

Emu

Royal Australasian Ornithologists Union

Lugar: Cardiff, Australia; Año: 2009 vol. 109 p. 192 - 197

0158-4197

Currently, the sex of Blue-fronted Amazons (Amazona aestiva) cannot be determined by in-hand methods as males and females are supposed not to differ in plumage colour and body size. We used discriminant function analysis to develop equations for determining the sex of Blue-fronted Amazons using in-hand measurements. We took seven morphological and one-plumage colour (percentage of yellow on the head) measurements from 202 birds in North-western Argentina. Sex of each individual was determined using DNA-based genetic techniques. For all morphometric measurements males averaged larger than females. Males also had a higher percentage of yellow plumage on the head than females. 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, tibia length, and head width) was more accurate and reliable for sex determination than single-measurements, classifying correctly 85% of the individuals. Our results show that Blue-fronted Amazons are sexually dimorphic for most body size characteristics and show sexual dichromatism in head plumage coloration, which allows to sex individuals by morphological variables that can be easily measured in the field.