Feather traits and ptilochronology as indicators of stress in Iberian Blackcaps Sylvia atricapilla

Abstract

This paper compares feather traits to explain diferences in stress between three Blackcap Sylvia atricapilla populations distributed along a N–S gradient of increasing drought in the Iberian Peninsula. Indices based on the width of growth bars, length, mass and fluctuating asymmetry (FA) of rectrices were examined for age efects and variation between populations along the gradient. The growth bars of juveniles (but not adults), feather mass, mass/length ratio and FA varied between populations (narrower bars, lighter feathers and increasing FA in the southern populations), providing evidence of increasing stress of moult in Blackcaps of drier Iberian regions.