The relationship between bird distribution and the botanical and structural characteristics of hedges.
The relationship was examined between the botanical and structural characteristics of the hedgerows of five Oxfordshire farms, and the bird populations associated with them, in a study carried out in April-July 1979. Multiple regression analysis demonstrated that, for this sample, bird-rich hedges tended to be tall and to have more species of shrub growing in them than did hedgerows in which few bird species were recorded. The overall density of birds in the hedgerows (measured per unit length), and the density of several individual species, were also positively correlated with hedgerow height, with the rate of occurrence of mature trees in the hedgerows, and with the presence of garden habitat close to the hedgerow. The extent of gaps in hedgerows had a significant negative effect on the overall abundance of birds, and on the abundance of two common species, the blackbird and dunnock. These observations are considered in terms of practical management of conservation - neglect of hedgerows leading to the development of gaps and excessive management in the form of cutting, are both likely to have a negative effect on the local abundance of many species.