Predicting the sex of the Sedge Warbler (Acrocephalus schoenobaenus) by discriminant analysis

Abstract

Sexual size dimorphism was examined in 273 immature Sedge Warblers (Acrocephalus schoenobaenus) caught in northern Poland during autumn migration in 2008 and 2009. Each individual was measured (wing, tail, head to bill, bill length, bill width, bill height, two measurements of tarsus width and hind claw length) and a blood sample was taken for molecular sexing. A forward stepwise discriminant function analysis was used and three discriminant functions were proposed for sexing Sedge Warblers. The first function, applied to the nine measurements, identified wing and bill length as the best measurements for sexing and correctly classified 82% of individuals. The second and third functions, ap, plied to only wing length and tail length, identified the former as the best single measurement, and these two correctly classified 83% and 82% individuals, respectively. These functions may be used as a tool for sexing Sedge Warblers when blood sampling is impossible, such as in historical ringing records. However, the functions may be valid only for young birds in north and central Europe measured by experienced ringers.