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 lowland-farming landscapes to provide a background against which decisions concerning 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/abundance of trees. The provision of cover and the botanical and structural complexity of the vegetation are also important. However, large hedges do not suit all species; birds tend to prefer hedgerow types which most closely resemble their usual non-hedgerow breeding habitat. The value of hedgerows to birds can be increased by combining them with other features such as headlands (for game birds), verges, wildflower strips, game and wild-bird cover and well-vegetated banks and ditches. The presence of well-grown, dead or decaying trees is beneficial to many species, providing nest holes, foraging sites and perches. Increasing the structural complexity of a hedgerow and its associated habitat may also reduce the incidence of predation. Hedgerows also provide physical shelter and roost sites and are an important source of winter food supplies, especially berries and other fruits. Some bird species, usually those whose primary habitat is woodland, live mainly within the hedgerow itself, whereas others are more dependent on the surrounding landscape to a greater or lesser extent. However, even the presence of woodland bird species is influenced by the availability and characteristics of alternative habitats in the surroundings and therefore hedgerows and their bird populations do not function as isolated patches. As linear landscape elements, hedgerows also provide safe cover for both local and larger-scale movements and may facilitate access to resources or habitat which might otherwise be too risky or too remote for birds to use or colonise. A number of recommendations for improving hedgerow habitat for birds are reiterated from an extensive literature and include combining hedgerows with other semi-natural habitat, providing a variety of structural types, maintaining good cover in the hedge-base, e.g. by excluding stock and herbicide, and avoiding excessive cutting. However, good hedgerow management has costs and is unlikely to be applied widely in the absence of national policy and funding. (C) 2000 Academic Press.