The influence of hedge structure, management and landscape context on the value of hedgerows to birds: A review

In this review, we discuss the value of hedgerows as bird habitat in lowlan d-farming landscapes to provide a background against which decisions concer ning hedgerow management might be evaluated The two most important factors positively associated with species richness and abundance of breeding birds in hedgerows are hedge sire (height/width/volume) and the presence/abundan ce of trees. The provision of cover and the botanical and structural comple xity of the vegetation are also important. However, large hedges do not sui t all species; birds tend to prefer hedgerow types which most closely resem ble their usual non-hedgerow breeding habitat. The value of hedgerows to bi rds can be increased by combining them with other features such as headland s (for game birds), verges, wildflower strips, game and wild-bird cover and well-vegetated banks and ditches. The presence of well-grown, dead or deca ying trees is beneficial to many species, providing nest holes, foraging si tes and perches. Increasing the structural complexity of a hedgerow and its associated habitat may also reduce the incidence of predation. Hedgerows a lso provide physical shelter and roost sites and are an important source of winter food supplies, especially berries and other fruits. Some bird speci es, usually those whose primary habitat is woodland, live mainly within the hedgerow itself, whereas others are more dependent on the surrounding land scape to a greater or lesser extent. However, even the presence of woodland bird species is influenced by the availability and characteristics of alte rnative habitats in the surroundings and therefore hedgerows and their bird populations do not function as isolated patches. As linear landscape eleme nts, hedgerows also provide safe cover for both local and larger-scale move ments and may facilitate access to resources or habitat which might otherwi se be too risky or too remote for birds to use or colonise. A number of rec ommendations for improving hedgerow habitat for birds are reiterated from a n extensive literature and include combining hedgerows with other semi-natu ral habitat, providing a variety of structural types, maintaining good cove r in the hedge-base, e.g. by excluding stock and herbicide, and avoiding ex cessive cutting. However, good hedgerow management has costs and is unlikel y to be applied widely in the absence of national policy and funding. (C) 2 000 Academic Press.