Voles – little giants @ Grimsö

23 October 2020

All regular wildlife surveys run as planned, where the most noticeable this fall is the strong peak in the vole populations (small rodents, e.g. Microtus spp.) with the 3rd highest numbers since this monitoring started at Grimsö 1973. To follow the vole dynamics is a classic aspect of wildlife ecology, since these ups and downs are key factors for some processes among also other species, for example that small game species like grouse and hares suffer less predation in good vole years. One of the common explanations for when vole peaks arise includes that the previous winter should have been snowy, with long periods of snow coverage, which allows for vole reproduction more or less throughout the year (in winter in the sub nival space where predation is relatively lower than on bare ground). However, the winter 2019-20 offered a rather poor and short termed snow coverage around Grimsö. So, there seems to be room for additional explanations!

Besides the grouse species that also show high numbers this year, the research area got a minor invasion of Great grey owls (Strix nebulosa) which otherwise is a rare guest in the region. Within Grimsö research area (13 000 ha) at least 10 reproductions were recorded (although not within any monitoring scheme).

The present strong peak in the vole population around Grimsö benefits many species, for example both generalist and specialist predators on small game. This Summer at least 10 pairs of Great grey owls reproduced within the research area, and the picture shows one of the parents feeding the young with a vole. Photographer: Rick Heeres