Sex determination of Iberian Azure‐winged MagpiesCyanopica cyanus cookiby discriminant analysis of external measurements

Abstract

Like all corvids, the Azure-winged Magpie Cyanopica cyanus is sexually monomorphic in plumage, making it difficult to distinguish between males and females in the field. We examined sexual size dimorphism in a population of Iberian Azure-winged Magpies C.c. cooki and used a discriminant function analysis based on five morphological characters to determine the sex of first-year and adult individuals. Females were significantly smaller than males for all tested variables within each age class except for keel length of first-year individuals. In both sexes, wing length of adults was greater than that of yearlings, but only males showed significant differences in tail length between age classes (longer in first-year birds). Stepwise discriminant analysis indicated that tail length and head plus bill length were the most accurate variables in a discriminant function model, predicting the sex of yearlings with about 90% accuracy. Adding wing length to the model yielded the same level of accuracy for adults. We propose a simple system to sex Iberian Azure-winged Magpies, using only two or three variables easily measured in the field, which provides classification with a high level of accuracy.

Sexing Black‐legged Kittiwakes by measurement

“…In many studies of birds where multiple measurements have been used to produce a discriminant function, virtually no advantage is gained by including a third value and often the second added little to the accuracy of sexing from one biometric measurement. Unfortunately, many studies have uncritically applied discriminant functions to sex birds and, for example, have not reported the gain in accuracy obtained by adding each additional parameter, eg Green (1982), Green & Theobald (1989), Brown et al (2003) and Alarcos et al (2007), amongst many. Including an additional factor always increases (by chance or otherwise) the proportion correctly sexed in the study sample.…”

Cohort effect on discriminant rate: the case of greater flamingo (<i>Phœnicopterus roseus</i>) chicks sexed with morphological characters

“…Our results demonstrate that the sex of greater flamingo chicks can be determined based on individual morphology using DFA and a subsample of individuals molecularly sexed. This method was also used for adult greater flamingos (Richter and Bourne, 1990) and other birds, where morphometric criteria may discriminate between males and females (Childress et al, 2005;Alarcos et al, 2007;Hurley et al, 2007;Ackerman et al, 2008;Herring et al, 2008;Lislevand et al, 2009;Herring et al, 2010).…”

“…The ability to correctly sex marked birds is crucial to most behavioral or ecological studies (Greenwood, 1980;Andersson, 1994;Short and Balaban, 1994;Childress and Bennun, 2002; Barbraud et al, 2003) and for the management and conservation of species (Zavalaga and Paredes, 1997;Fernandez-Juricic, et al, 2009). However, sex determination in immature and adult individuals where the plumage is similar in both sexes based only on external morphological characters is often difficult (Cuthill et al, 1999).…”

Use of external biometrics to sex Carrion CrowCorvus corone, RookC. frugilegusand Western JackdawC. monedulain Northern England

“…Previous studies have explored sexing members of the Corvidae family using a range of biometrics such as mass, wing length, head-plus-bill length, skull length, tarsus length, bill length and bill depth (Green 1982, Reese & Kadlec 1982, Kavanagh 1988, Clark et al 1991, Kenward et al 2004, Alarcos et al 2007, Lee et al 2007 with high levels of accuracy (90-100%). The wing and minimum tarsus length of Western Jackdaws have been previously used to sex 65% of 141 birds with 96.7% accuracy (Henderson 1991) and wing and bill length of Rooks have been used to calculate a discriminant function with 98.7% accuracy (Green 1982).…”