We studied the habitat requirements of a vulnerable butterfly, Erebia aethiops, in a grassland-forest mosaic within a nature reserve. This species inhabits seemingly abundant habitats such as forest edges, but it is declining in many parts of Europe.
We analysed mark-recapture data, focusing on the effects of distinct vegetation structures, nectar sources and management regimes on population density and mobility.
Adult E. aethiops preferred abandoned grasslands and small open enclaves surrounded by forest; i.e. highly heterogeneous habitats. Male densities were higher in sparse woodlots, female densities at grassland patches. These intersexual differences in habitat use emphasise the need for heterogeneous vegetation.
Like other inhabitants of traditional woodlands, E. aethiops suffers from canopy closure, leading to its retreat to transitional structures such as forest edges or abandoned grasslands. Such preferences are in conflict with regular grassland management, necessary for conserving many other grassland organisms. Therefore, sparse woodlands containing forest free enclaves should be restored to protect this and other woodland organisms.