Dispersion, Migration, and Movements

Dispersion, Migration, and Movements of the Boreal Owl (Aegolius funereus)

Northern populations are described as nomadic—that is, wandering and unsettled. Males exhibit greater site fidelity to breeding grounds than females (Korpimäki 1986), although in Central Europe, breeding site fidelity has been documented in both sexes (Schwerdtfeger 1984). Nomadic females disperse annually from western Finland over distances of 500–600 km. Differences in dispersal between males and females are often linked to periodic fluctuations in prey abundance and winter food availability. Food shortages stimulate females to disperse, whereas males experience an increased need to defend their nest cavity, which reinforces their site fidelity (Korpimäki et al. 1987).
In Central Europe, adult birds are sedentary or nomadic over short distances (up to 20 km), whereas young birds tend to disperse into surrounding areas, sometimes over greater distances. However, some ringing recovery records deviate from this pattern: for example, an adult owl ringed in late August in eastern Slovakia was recaptured in October of the same year on the Baltic coast (720 km); an owl ringed in Russia in March as an adult was found in December of the same year in northern Slovakia (year of ringing and recovery not specified, author's note). By the end of 2002, a total of 26 ringing recovery records were known in the Czech Republic and Slovakia; however, all recaptures pertain to females controlled in nest boxes (Cepák et al. 2008).

Author: Karel Poprach