Influence of snow cover on food hoarding in Pygmy Owls Glaucidium passerinum

Voles are the most preferred prey of Pygmy Owls (Glaucidium passerinum) in Northern Europe, where the extensive snow cover may decrease the availability of voles. Snow covermay thus cause changes in the diet fromwhat is expected on the basis of prey abundance alone. Food hoarding behaviour of Pygmy Owls was examined in relation to snow cover. Pygmy Owls hoard small birds and mammals in tree holes and nest boxes on their autumn andwinter territories.During fivewinters,we examined hoarded prey items from artificial hoarding boxes provided to Pygmy Owls in central Finland. Themost intensive food hoarding periods occurred before the fall of snow, during which 73% of prey items were hoarded. Presence or absence of snow cover did not affect the number of hoarded birds, but snow cover dramatically lowered the number of hoarded voles. Pygmy Owls began to exploit caches before the beginning of the snowy season and stopped exploitation in spring.According to the high utilization degree of the hoarded prey, especially during the period with permanent snow cover, we suggest that the Pygmy Owl’s food hoarding behaviour acts as a buffer for seasonal variation in food supply.

Halonen, T. Mappes, T. Meri & J. Suhonen, Ornis Fennica 84:105-111. 2007