Hedgerows and forest edges – valuable structures in farmland

The birds that inhabit hedgerows and forest edges are originally woodland species. Some live in the forest’s shrub layer, others inhabit large windthrow areas, while still others occupy areas where woodland growth is hampered by unfavourable conditions, giving way to semi-open scrubland. Red-backed Shrike, common Whitethroat, Tree Pipit and Yellowhammer fall into these categories.

35 bird species regularly occupy hedgerows. While numerous publications exist on «common hedgerow birds» such as Garden Warbler, common Whitethroat, Red-backed Shrike or Yellowhammer, surprisingly little has been published on the composition of breeding-bird communities in hedgerows and forest edges. In particular, the composition of bird communities in typical hedgerow landscapes in different regions and altitude zones in Switzerland is not well understood. One of the few studies to give a comprehensive description of breeding birds in a hedgerow landscape in Switzerland comes from the inner-Alpine Albula Valley GR. On 400 ha of land between 880 and 1180 m, the most common hedge-nesting birds were, in order of abundance, Eurasian Blackcap, Yellowhammer, Red-backed Shrike, Eurasian Blackbird, Garden Warbler, Eurasian Magpie and Eurasian Green Woodpecker. In 2009–2011, the project «Mit Vielfalt punkten/Scoring with biodiversity», initiated by the Swiss Ornithological Institute and the Research Institute of Organic Agriculture, studied the bird communities on 133 farms between Bern and Zurich. The species most attracted to hedgerows were Garden Warbler, Red-backed Shrike, Yellowhammer, Eurasian Magpie, European Goldfinch and Short-toed Treecreeper.

According to the territory mapping surveys in kilometre squares (1 × 1 km) in 2013–2016, 40 out of 50 woodland species with sufficient data favour forest edges. The preference is most pronounced in Common Nightingale, Lesser Whitethroat, Redpoll, Ring Ouzel, Black Grouse, Citril Finch and Western Bonelli’s Warbler (in order of decreasing abundance). By contrast, only ten woodland birds were more abundant than expected in the forest interior. The species showing the strongest preference for the forest interior were (in this order): Northern Goshawk, Middle Spotted Woodpecker, Hawfinch, Stock Dove, Tawny Owl, Black Woodpecker and Common Woodpigeon.

Eurasian Blackcap, Garden Warbler, Greater Whitethroat, Red-backed Shrike and Yellowhammer, all typical hedge-nesting birds, have very different population trends. The trends of Red-backed Shrike and Garden Warbler were initially positive, but populations have collapsed since the late 1990s. The Yellowhammer shows small fluctuations over the long term. Following an initial decline, the Greater Whitethroat population is showing signs of recovery. The Eurasian Blackcap, on the other hand, a species that also often nests in woodland, is increasing significantly. Apart from the quality or quantity of hedge habitat, other factors such as conditions in the wintering grounds and stopover sites, the changing food supply (especially insects) and the population trend of the woodland population appear to influence the «hedge nesters».

Hedgerows and forest edges can differ widely in terms of quality. Long, broad hedgerows and forest edges with a high proportion of thornbushes, a dense shrub layer, the presence of several woody species and plenty of old growth and deadwood are especially attractive for birds. Old hedgerows, where these structures are more common, are more frequently occupied by birds than young hedges. The presence of a broad fringe managed at low intensity and additional hedges or other near-natural structures has a positive impact on breeding birds. Some birds (e.g. Greater Whitethroat, Red-backed Shrike) favour low-growing shrub hedges, but the presence of trees increases species richness.

Unfortunately, the quality of hedgerows in many areas of Switzerland is unsatisfactory. It would take relatively little effort to enhance the ecological value of hedgerows and forest edges, as demonstrated by a hedge-improvement project («Aktion Dornröschen») initiated by BirdLife Lucerne and supported by the Canton of Lucerne. Within just a few years, the quality of 112 km of hedges was significantly improved.

Hedgerows and forest edges are among the most important habitat features for breeding birds in farmland. We need to focus on improving the ecological quality of hedges and increasing the stock by replanting hedges where they have been removed.

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