An uneven sex ratio of migrant long‐eared Owls

Sex ratio of accidentally killed Long‐eared OwlsAsio otusin Norway

“…When the ratio of 28:8 F:M recorded by Harvey & Riddiford (1990) in Great Britain is compared with the Norwegian winter data, the difference in sex ratio is statistically highly significant (x 2 ,=10.57, P<0.0\).…”

“…1). This movement maybe extended further west towards the British Isles (Harvey & Riddiford 1990) where mostly females were found among migrating Long-eared Owls. Armitage (1968) and Lunn (1992) point out that immigrant Long-eared Owls supplement the British population during winter, and that these birds were possibly of continental origin.…”

“…It seems that individuals migrating over long distances mainly originate from Fennoscandic and Russian populations north of 50°N, and migration appears to take place in a southsouthwesterly direction. Harvey and Riddiford (1990) report a significantly uneven sex-ratio in favour of females among migrating Longeared Owls on Fair Isle, Shetland. They suggest that these birds originate from Fennoscandia, but lack information to back up their suggestion.…”

Age Structure of the Long-Eared Owl (Asio otus) Migration at Bukowo-Kopań Station (Southern Baltic Coast) in Autumns 1996-2003

“…We also cannot say that this owl represents typical migratory species because it is known that especially adult males show tendency to breeding site fidelity. So if adult males do not leave breeding grounds as was shown in Norway (Harvey and Riddiford 1990) then adults should make only a 25% of birds caught during autumn migration. From our experiences we know that some adult males do migrate as we caught them several times at the Polish coast of the Baltic Sea.…”

“…It is possible that adults, which show stronger breeding site fidelity than young ones (Cramp andSimmons 1985, Glue andNilsson 1997), migrate in higher numbers only when food resources are too scarce to survive. Number of late adult migrants could be correlated with sex structure of migrating birds males have stronger site fidelity (Harvey and Riddiford 1990) so probably they leave breeding territory only in extremely bad conditions.…”