Responses of woodland birds to increasing numbers of deer: a review of evidence and mechanisms

Increases in grazing pressure within woodland can profoundly affect the spe cies composition of bird communities, but few studies have been conducted i n Europe and there is a lack of relevant experimental research. A principal mechanism by which deer can alter bird communities is through reduction of low foliage density. High deer densities may also be implicated in a varie ty of indirect effects on birds mainly by altering food resources and nest losses through predation. Breeding populations of migrant birds appear to b e especially vulnerable to increased deer densities in lowland British wood s because these species generally require dense understorey structures. Evi dence is presented that, possibly with the exception of nightingale (Luscin ia megarhynchos), populations of breeding migrants may persist in lowland w oods with increasing deer densities, provided that young regeneration is ad equately protected. However, a priority for research is to understand how b ird communities respond to different densities of deer.