Living at the limit: Ecology and behaviour of Tawny Owls Strix aluco in a northern edge population in central Norway.

Tawny Owl (Strix aluco) Science Article 6

abstract

The Tawny Owl Strix aluco was studied at the northernmost limit of its geographical range (63degree20’N) in order to investigate how this extremely residential species has adapted to the marginal conditions of its northern outpost. The presence of nemoral forest vegetation was crucial for the occurrence of the species. The mean annual home range size of radio tagged females was much larger than reported in any other study. The winter home ranges were, on average, 54% larger than those in summer. In the summer, range size was negatively correlated with the proportion of mixed deciduous/coniferous forest within 1km of the nest. This could be explained by the abundance of bird prey, which comprised 61% of the summer diet. In the winter, no significant correlation’s with home range sizes were found. During this season, mammals comprised 95% of the diet. In extreme cases, females left the nesting area for prolonged periods during the non-breeding season. We conclude that even a species known to be notoriously residential can express a high degree of plasticity in its ranging behaviour when population densities are low, at least among the females. However, the environmental and social factors leading to some females leaving their nest areas in the non-breeding season are more complex than the result of mere lack of food

Sunde P., Overskaug K., Bolstad J.P. & Oien IJ., ARDEA 89 (3): 495-508.

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