The effects of deer browsing on woodland structure and songbirds in lowland Britain
Version of Record online: 23 NOV 2007
Volume 149, Issue Supplement s2, pages 119–127, November 2007
How to Cite
GILL, R. M. A. and FULLER, R. J. (2007), The effects of deer browsing on woodland structure and songbirds in lowland Britain. Ibis, 149: 119–127. doi: 10.1111/j.1474-919X.2007.00731.x
- Issue online: 23 NOV 2007
- Version of Record online: 23 NOV 2007
- Received 5 April 2007; revision accepted 20 April 2007.
The effects of deer in woodlands are known to result in habitat changes which can be detrimental to songbirds. In the first part of the paper we review the effects that deer may have on critical resources for woodland birds. The principal mechanism by which deer may affect habitat quality is through the reduction of low woody vegetation, which forms a key element of the preferred habitat of several species – this may be associated with loss of nest-sites, increased exposure to predators and reduction of food. The second part of the paper presents new evidence for the impacts of deer on vegetation structure, and how they may be contributing to the declines of some woodland songbirds in Britain. Results from extensive studies of deer at 13 woodland sites in England and Wales reveal that understorey foliage density decreases significantly with increasing deer density. Reduction of foliage was greatest at below 1.5 m above ground. We also report preliminary results of an experimental comparison of songbird densities between deer-fenced and unfenced areas of young coppice woodland in eastern England. In this study, deer browsing caused extensive impacts on vegetation structure in young coppice, though there was considerable variation between plots. Deer browsing resulted in reduction of canopy cover, reduction in density and cover of understorey vegetation, and an increase in grass cover. Abundance of bird species using the understorey, including all migrants, was significantly higher in coppice where deer were excluded. These results lend support to the hypothesis that deer are at least partly responsible for causing declines in some British bird populations, but they do not eliminate the possibility that increased shading is also responsible for changes in woodland structure. At present there is much spatial variation in deer densities in Britain so that impacts on low vegetation and habitat quality for birds are not expected to be the same in all regions. However, with continuing increases in deer numbers it is to be expected that such impacts will become more widespread.