Hedgerows and forest edges – valuable structures in farmland
In otherwise open country, hedges provide shelter, nest sites and hunting perches. Forest edges, like all transition zones between different habitats, are especially rich in species. But most hedgerows and forest edges do not offer the habitat quality that breeding birds require. The need for ecological restoration is great.
Hedges and copses increase habitat connectivity and have a positive effect on species richness in farmland, including breeding birds. Tapered forest edges with dense shrubs and a species-rich herb fringe have a similar function.
Until about 1950, the landscapes of the Central Plateau were dominated by a mosaic of small, hedged plots. Following large-scale land consolidation, many hedges were cleared, a process that continued until about 1990. Since then, the number of hedges has increased again due to shrub encroachment on embankments (e.g. in terraced fields) and intentional replanting. Between 1989 and 2003, hedges in Switzerland increased by 62 km annually, reaching a total length of 10 334 km in 2003.
Woodland species are typical inhabitants of hedgerows and forest edges
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.
Population trends of birds in hedgerows and forest edges
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».
Urgent need for more thorny hedges
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.
Berg, Å. & T. Pärt (1994): Abundance of breeding farmland birds on arable and set-aside fields at forest edges. Ecography 17: 147–152.
Birrer, S. & F. X. Kaufmann (2014): Dornröschen, wach auf! Ornis 2014/4: 15–17.
Bundesamt für Umwelt (2007): Länge linearer Landschaftselemente. Stand: April 2007. Basisdaten aus dem Biodiversitäts-Monitoring Schweiz BDM E4. Bundesamt für Umwelt, Bern.
Christen, W. (1988): Brutvögel zweier Hecken in der Aareebene. Vögel der Heimat 59: 36–38.
Ewald, K. C. & G. Klaus (2009): Die ausgewechselte Landschaft. Vom Umgang der Schweiz mit ihrer wichtigsten natürlichen Ressource. Haupt, Bern.
Flückiger, P. F., H. Bienz, R. Glünkin, K. Iseli & P. Duelli (2002): Vom Krautsaum bis ins Kronendach - Erforschung und Aufwertung der Waldränder im Kanton Solothurn. Mitt. Nat.forsch. Ges. Kanton Solothurn 39: 9–39.
Glutz von Blotzheim, U. N. & K. M. Bauer (1966–1997): Handbuch der Vögel Mitteleuropas. Bd. 1–3 von K. M. Bauer & U. N. Glutz von Blotzheim bearbeitet, Bd. 4–7 von U. N. Glutz von Blotzheim, K. M. Bauer & E. Bezzel sowie Bd. 8–14 von U. N. Glutz von Blotzheim & K. M. Bauer. Mehrere Bände seither in der 2., durchges. Aufl. Akademische Verlagsgesellschaft, Wiesbaden (bis 1982) bzw. Aula, Wiesbaden.
Hinsley, S. A. & P. E. Bellamy (2001): The influence of hedge structure, management and landscape context on the value of hedgerows to birds: a review. J. Environ. Manage. 60: 33–49.
Horch, P. & O. Holzgang (2006): Hecken für Heckenbrüter: Erkenntnisse aus den drei Inventaren 1979, 1988 und 1999 im Kanton Thurgau. Ornithol. Beob. 103: 39–56.
Kohli, L. & S. Birrer (2003a): Diversité envolée dans la zone agricole - état des habitats de notre avifaune. Avifauna Report Sempach 2. Station ornithologique suisse, Sempach.
Kohli, L. & S. Birrer (2003b): Verflogene Vielfalt im Kulturland - Zustand der Lebensräume unserer Vögel. Avifauna Report Sempach 2. Schweizerische Vogelwarte, Sempach.
Korner, P., R. Graf & L. Jenni (2017): Large changes in the avifauna in an extant hotspot of farmland biodiversity in the Alps. Bird Conserv. Int. 6: 1–15.
Krüsi, B. O., M. Schütz & S. Tidow (1997): Waldränder in der Schweiz. Ökologischer Zustand, botanische Vielfalt und Aufwertungspotential. Schweiz. Wald 97: 5–19.
Laiolo, P. & A. Rolando (2005): Forest bird diversity and ski-runs: a case of negative edge effect. Anim. Conserv. 7: 9–16.
Müller, M. (1996): Das Engadin: Lebensraum für Brutvögel der offenen und halboffenen Kulturlandschaft. Jahresber. Nat.forsch. Ges. Graubünden 108: 39–119.
Ott, R. & R. Graf (2010): Die Vogelwelt in der Heckenlandschaft Albulatal - Brutvogelkartierung 2009. Parc Ela Region Albula-Bergün, Savognin-Bivio.
Pfister, H. P., B. Naef-Daenzer & H. Blum (1986): Qualitative und quantitative Beziehungen zwischen Heckenvorkommen im Kanton Thurgau und ausgewählten Heckenbrütern: Neuntöter, Goldammer, Dorngrasmücke, Mönchsgrasmücke und Gartengrasmücke. Ornithol. Beob. 83: 7–34.
Zellweger-Fischer, J., J. Hoffmann, P. Korner-Nievergelt, L. Pfiffner, S. Stoeckli & S. Birrer (2018): Identifying factors that influence bird richness and abundance on farms. Bird Study 65, doi: 10.1080/00063657.2018.1446903.