Moult and Morphometrics of the Pallid SwiftApus pallidusin Northwestern Italy

Abstract

We examined moult patterns and body morphometry of pallid swifts at two locations in NW Italy, by sampling 352 birds at their nests from July through October over a 20-year period. Birds were sexed by behaviour at the nest. We found no sexual dimorphism in 8th primary length, tail length, depth of the tail fork, rectrices T5–T4 tip delta length or body mass. We found a significant difference between the sexes in wing length (females mean: 174.7 mm, range 169–184; males: 177.0 mm, range 169–191), but because of extensive overlap it cannot be used to determine the sex of most individuals. Measurements of birds recaptured in following years did not differ with increasing age. Birds began the moult in July. Moult was estimated to last about five months, from July until November–December, and was not completed on our study sites. Females and males did not differ in the timing and progression of the moult during the season. About one-third of individuals did not replace the 9th or 10th (outermost) primary, with a complex pattern of retention and substitution in sequence year after year. The overlap of breeding season and moult in this population appears to be higher than that reported for two other Italian swifts and is similar to that found in tropical swift species.