Moult and body condition in Long-tailed Tits Aegithalos caudatus

Abstract

Moult is a key life-cycle event associated with reduced flight performance and high energetic demands. Juvenile Long-tailed Tits Aegithalos caudatus have a complete post-juvenile moult so that both adults and juveniles will be undergoing a full moult at similar times of year. Given lower foraging experience and developmental immaturity of juveniles, we might predict differences between adults and juveniles in moult parameters and the effect of moult progression on body mass. The aim of this study was to test these predictions by analysing moult data for Long-tailed Tits in the northeast of England. Juveniles started moult 12 days later than adults but the duration of moult was similar. The timing of moult varied between years; correlations between year-to-year change in moult timing and spring temperatures suggest that the timing of moult and breeding are linked. Raggedness scores, a measure of moult speed, remained relatively constant during the central phase of moult and were independent of moult score. Although wing length made the greatest contribution to body mass, the best statistical model included raggedness as a factor contributing to variation in body mass, suggesting that faster moulting may be associated with lower body mass. The analysis did not support the prediction that age is a significant factor affecting body mass during moult.