The impacts of deer on woodland butterflies: The good, the bad and the complex

Feber RE, Brereton TM, Warren MS, Oates M

Deer grazing is an important feature of many key butterfly habitats in Britain, yet few data are available on its impacts. Butterfly populations can be affected in a number of ways, through effects on the local availability of larval food-plants or nectar sources, to larger-scale changes in habitat structure and management. Many woodland butterflies have historically relied on clearings in coppiced woodland, but current high numbers of roe deer (Capreolus capreolus), and to a lesser extent fallow deer (Dama dama), can severely reduce tree regrowth and are now a major disincentive to the maintenance of this traditional form of management. In contrast, deer grazing may be very beneficial in some woodland habitats. In Scotland, most colonies of the threatened pearl-bordered fritillary (Boloria euphrosyne) rely to some extent on grazing by deer, to slow down natural regeneration and maintain open bracken (Pteridium aquilinum) habitats in canopy gaps and along woodland edges. Such areas have recently been targeted by schemes to encourage native woodland, but the fencing out of deer and other grazing animals can lead to rapid loss of these crucial woodland habitats. Far more research is needed to determine the full extent of these impacts and implications for conservation programmes.