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.