Breeding biology and food of the great grey owl, Strix nebulosa, in northeastern Finnish Forest Lapland

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In 1969, one, and in 1974, six nests of the Great Grey Owl, Strix nebulosa, were found in the central (67°N, 29°E) and southern (66°30'N: 29°10'E) parts of Salla, NE Finnish Forest Lapland. In 1974, pellets were collected at four nests and 504 hours of observation were carried out at one nest. Five of the seven nests were situated on fresh heaths covered by spruce dominated mixed forests. All the nests were near a bog or a clear-cut area. Five of the nests were in old nests of birds of prey, one in an old nest of a Magpie and one on a stump. The Great Grey Owls did not bring any nest- building material to their nests. They totally lacked nest-building movements. Only the female incubated. It left its nest unattended only 0.63 % of the time. At the same time only the male hunted. It fed the female at the nest with from three to four vole-sized animals per day. During the incubation period activities at the nest were concentrated in the darker half of the diel cycle. On the contrary, during the nestling period feeding and other activities occurred throughout the day. According to pellet analyses Microtus species (M. agrestis and M. oeconomus) formed 87.6 % of the prey. The proportion of Clethrionomys glareolus was 9.9 % and that of Sorex spp. 2.5 %. At the end of the nestling period a young hare (Lepus timidus) was brought to the nest and eaten there. During the nestling period as many as 14 vole-sized animals were brought (mainly by the male) daily to the nest. In addition to man, large and hawk- shaped birds flying in the vicinity of the nest were regarded by the Great Grey Owls as a threat to it. It is concluded that the sexual dimorphism of the Great Grey Owl has an important biological meaning. The relatively large body size of the female is needed for thermoregularion during the incubation period and the relatively small body size of the male for quickness in hunting.

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Reference Code: A77PUL01IDUS

Full Citation: Pulliainen, E., and K. Loisa. 1977. Breeding biology and food of the great grey owl, Strix nebulosa, in northeastern Finnish Forest Lapland. Aquilo Series Zoologica 17: 23-33.

Location: ANIMAL EF: STRIX NEBULOSA