Age and sex dimorphism in the Canary Blue Tit Cyanistes teneriffae teneriffae on the island of Tenerife, Canary Islands

Abstract

The Canary Blue Tit Cyanistes teneriffae has recently been split off from the Common Blue Tit Cyanistes caeruleus as a separate species. Live biometrics from across the entire distribution on the island of Tenerife (subspecies teneriffae teneriffae) are reported. Results suggest that first-year birds had similar bill shape to adults but differed in wing length, tarsus, tail and mass, being smaller on average. A high degree of sexual size dimorphism is reported, males being on average larger than females for wing length, bill length, bill depth and tarsus. A classification tree between the sexes showed that wing length and bill depth were the most important variables and correctly classified males in all occasions (i.e. male = wing length > 62.5 mm; bill depth > 3.7 mm, 100% correctly classified) but for practical sexing in the field it is recommended to use wing length as a reliable sexing criterion (wing length > 62.5 = male, 96% correctly classified). This high degree of sexual size dimorphism observed suggests a high sexual selection in the Canary Blue Tit.