Intersexual difference in early natal dispersal: abrupt departure by females and gradual emigration by males in Tengmalm’s Owl Aegolius funereus

Abstract

The decision to emigrate from the natal area can influence future fitness prospects, yet detailed data on sex-specific juvenile dispersal behaviour is still lacking for most bird species. We tracked 13 radio-tagged Tengmalm’s Owl Aegolius funereus juveniles from 13 different nests from fledging to independence and onwards. Six out of the seven female juveniles departed abruptly and disappeared from the natal area. In contrast, only one male juvenile departed abruptly, whereas the other five males and one female remained in the study area until tracking was terminated. We propose two alternative interpretations: (1) females initiated natal dispersal earlier than males, or (2) the manner of dispersal differed between the sexes, with females departing abruptly, and males moving gradually out of the natal area. We found no statistically significant influence of body condition or date of independence on dispersal behaviour. We suggest that early onset of dispersal and fast movements out of the natal area may increase a juvenile female’s chances of successful breeding in the following spring. In contrast to females, male Tengmalm’s Owls rarely breed as 1-year-olds, and the benefits of early/abrupt dispersal may be lower for juvenile males. We suggest that female-biased natal dispersal in Tengmalm’s Owl may come about through relatively higher lifetime reproductive success of early dispersing in females than in males.