AGE-RELATED EVOLUTION OF SEXUAL DIMORPHISM IN THE RED-NECKED NIGHTJARCAPRIMULGUS-RUFICOLLIS

Some morphological and sexual characters were measured in juvenile, fi rst-year and adult Red-necked Nightjars in SW Spain. We found signific ant age-related growth in wing, tail and body mass, first-year birds b eing heavier than adults. Adults showed sex differences in tail and wi ng lengths, and the size of tail and wing spots differed between males and females of all age classes. There was not any difference in the n umber of wing spots, and juvenile males had a lower number of tail spo ts than older males. An age-related increase in sexual dimorphism was found to exist by size increase of wing spots in males. Since wing and tail spots are exhibited in courtship displays, the elongation of the se secondary sexual characters could be related to mate choice mechani sms.