Ardea
Official journal of the Netherlands Ornithologists' Union

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Post P. & Götmark F. (2006) Seasonal changes in Sparrowhawk Accipiter nisus predation: prey vulnerability in relation to visibility in hunting habitats and prey behaviour. ARDEA 94 (1): 77-86
Studies of Sparrowhawk Accipiter nisus predation have revealed a seasonal change in the predation risk of many prey species during spring and summer. Several species nesting in forest experienced decreasing risk of predation, while species in semi-open habitats (farmland, edge habitats and villages) faced increasing risk. The reason for this change could be that leafing and growth of ground vegetation during spring hamper detection and catching of prey in forest compared to villages and edge habitats, thus forcing Sparrowhawks to hunt in semi-open habitats with better visibility. We examined this possibility by measuring visibility of artificial prey in four different habitats, deciduous and coniferous forest, urban areas and edge habitats, from April to July. Although visibility decreased more in deciduous habitats than in urban or coniferous habitats from April (before leafing) to June (most vegetation developed), visibility was not lower in deciduous forest than in urban or edge habitats in the summer. However, birds observed in urban habitats were on average more exposed than birds in forest in April, and this difference increased in May. In May, urban birds were also found significantly closer to the ground than forest birds. These results suggest that prey behaviour, rather than vegetational change, determine seasonal changes in predation risk of the prey species.


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