Biometrics of Citril Finch Serinus citrinella in the west Pyrenees and the influence of feather abrasion on biometric data

Biometric data are an essential component of studies into the breeding biology of bird populations. Citril Finches Serinus citrinella in the Pyrenees mainly feed on pine seeds, and coniferous habitats in the west Pyrenees are of significant conservation importance. The aim of this study was to increase our understanding of morphological variation in Citril Finches breeding in the west Pyrenees, north Iberia, within a region of grasslands and woodlands of Scots pine Pinus sylvestris. Individuals (1,118) were mist netted, ringed and measured. Wing and tail length were influenced by feather abrasion, particularly in juvenile birds. Overall, male Citril Finches were larger than females for all structural and flight-feather measurements (wing, tail, tarsus and culmen length, bill depth and width and lower mandible length), and adults were larger than young birds (except for tail length, culmen length and bill depth). There was significant year-to-year variation for all measurements apart from tail length, but the reasons for this are unknown. Principal Components Analyses (PCA) were used to analyse wing and bill morphology. Adult birds had narrower, more pointed wings than young birds, and the wing shape in males was more pointed than in females. There were only sex-specific differences in bill morphology, with males having more robust bills. We obtained a discriminant function to classify the sex of birds before their post-juvenile moult.

Daniel Alonso and Juan Arizaga, Ringing & Migration (2006) 23, 116-124