Action: Manage hedges to benefit birds
Key messagesRead our guidance on Key messages before continuing
- The one study of six that investigated species richness found no difference in species richness between a UK site with wildlife-friendly hedge management and three control sites.
- Seven studies from the UK and Switzerland, five replicated, found that some species studied increased in relation to managed hedges or were more likely to be found in managed hedges, compared to other habitats. Two investigated several interventions at once.
- One replicated study found that species that showed positive responses to hedge management in some regions showed weak or negative responses in other parts of the UK. Four studies from the UK found that some species declined or showed no response to wildlife-friendly management of hedges.
Hedges can be key habitats for farmland biodiversity, but they may need managing to maximise their value. Managing hedges to benefit wildlife involves one or more of the following management changes: reduce cutting frequency; reduce or avoid spraying; mowing vegetation beneath hedgerows or filling gaps in hedges.
Supporting evidence from individual studies
A 2000 literature review (Aebischer et al. 2000) found that the UK population of cirl buntings Emberiza cirlus increased from between 118 and 132 pairs in 1989 to 453 pairs in 1998 following a series of schemes designed to provide overwinter stubbles, grass margins, and beneficially managed hedges and set-aside. Numbers on fields under the specific agri-environmental scheme increased by 70%, compared with a 2% increase elsewhere.
A small replicated controlled study from May-June in 1992-8 in Leicestershire, England (Stoate 2002), found that the abundance of nationally declining songbirds and species of conservation concern significantly increased on a 3 km2 site where hedges were managed to benefit wildlife (alongside several other interventions), although there was no overall difference in bird abundance, species richness or diversity between the experimental and three control sites. Numbers of nationally declining species rose by 102% (except for Eurasian skylark Alauda arvensis and yellowhammer Emberiza citronella). Nationally stable species rose (insignificantly) by 47% (eight species increased, four decreased). The other interventions employed were: ‘Create beetle banks’, ‘Plant nectar flower mixture/wildflower strips’, ‘Plant wild bird seed cover strips’, ‘Provide supplementary food’, ‘Control predators’ and ‘Reduce pesticide or herbicide use generally’.
A replicated site comparison study across eleven areas in the Swiss plateau between 1998 and 2001 (Herzog et al. 2005) found that the centres of territories of hedgerow birds were significantly more frequent in or near Ecological Compensation Areas than expected by an even distribution across the landscape (293 territories found in ECA hedgerows), suggesting that hedgerow birds were attracted to or favoured by these areas. Territories of breeding birds were mapped in 23 study areas, based on three visits between mid-April and mid-June.
A replicated study in February 2008 across 97, 1 km2 plots in East Anglia, England (Davey et al. 2010), found that four farmland birds showed strong positive responses to field boundaries (hedges and ditches) managed under agri-environment schemes. These were blue tits Parus caeruleus (also called Cyanistes caeruleus), dunnock Prunella modularis, common whitethroat Sylvia communis and yellowhammer. A further five (Eurasian blackbird Turdus merula, song thrush T. philomelos, Eurasian bullfinch Pyrrhula pyrrhula, long-tailed tit Aegithalos caudatus and winter wren Troglodytes troglodytes) showed weak positive responses and Eurasian reed bunting Acrocephalus scirpaceus showed a weak negative response. The boundaries were classed as either hedges, ditches or hedges and ditches and most were managed under the Entry Level Stewardship scheme.
A replicated site comparison of 2,046, 1 km squares of agricultural land across England in 2005 and 2008 (Davey et al. 2010) found that management of hedges and ditches (see ‘Manage ditches to benefit wildlife’) under Entry Level Stewardship did not have clear impacts on farmland bird species. Management had significant positive impacts on five species in at least one region of England, but these effects were often very weak and four of the same species showed negative responses in other regions. The other five ‘hedgerow species’ investigated were never positively associated with boundary management. Generally, effects appeared to be more positive in the north of England.
A replicated 2010 site comparison study of 2,046 1 km² plots of lowland farmland in England (Davey et al. 2010) found that three years after the 2005 introduction of the Countryside Stewardship Scheme and Entry Level Stewardship schemes, there was no association between the length of hedgerow managed according to the agri-environment scheme and farmland bird numbers. Hedgerow specialist species, including the yellowhammer Emberiza citrinella and common whitethroat, showed no significant population response, whereas there were greater numbers of common starling Sturnus vulgaris on arable, pastoral and mixed farmland with hedgerow management. For example, in mixed farmland plots starling populations increased by 0.2 individuals for each 1 km of hedgerow. On the other hand, the grey partridge Perdix perdix appeared to be detrimentally affected, with an apparent decline of 0.3 individuals for every 1.1 km of hedgerow managed according to the agri-environment schemes. The 2,046 1 km² lowland plots were surveyed in both 2005 and 2008 and classified as arable, pastoral or mixed farmland. Eighty-four percent of plots included some area managed according to the schemes. In both survey years, two surveys were conducted along a 2 km pre-selected transect route through each 1 km² square.
A replicated site comparison study on farms in two English regions (Field et al. 2010) found that summer yellowhammer numbers were significantly higher in hedges under environmental stewardship management than in conventionally managed hedges. On East Anglian farms, this was true for both Entry Level Stewardship and Higher Level Stewardship hedge management options (estimated >1.5 yellowhammers/m in Higher Level Stewardship hedges compared to <0.5 yellowhammers/m in conventional hedges). On farms in the Cotswolds, UK, it was only true for hedges managed as ‘high environmental value hedges’ under Higher Level Stewardship (estimated 0.5 yellowhammers/m), while hedges managed under Entry Level Stewardship did not have more yellowhammers than conventional hedges (estimated <0.2 yellowhammers/m). Hedgerows managed under Entry Level Stewardship are cut every two or three years in winter only. Surveys were carried out in the summers of 2008 and 2009, on up to 30 Higher Level Stewardship farms and 15 non-stewardship farms in East Anglia, and up to 19 Higher Level Stewardship and 8 non-stewardship farms in the Cotswolds. This study also discusses several other interventions.
- Aebischer N.J., Green R.E. & Evans A.D. (2000) From science to recovery: four case studies of how research has been translated into conservation action in the UK. Pages 140-150 in: J.A. Vickery, P.V. Grice, A.D. Evans & N.J. Aebischer (eds.) The Ecology and Conservation of Lowland Farmland Birds. British Ornithologists' Union, Tring.
- Stoate C. (2002) Multifunctional use of a natural resource on farmland: wild pheasant (Phasianus colchicus) management and the conservation of farmland birds. Biodiversity and Conservation, 11, 561-573
- Herzog F., Dreier S. & Hofer G. (2005) Effect of ecological compensation areas on floristic and breeding bird diversity in Swiss agricultural landscapes. Agriculture, Ecosystems & Environment, 108, 189-204
- Davey C.M., Vickery J.A., Boatman N.D., Chamberlain D.E. & Siriwardena G.M. (2010) Entry Level Stewardship may enhance bird numbers in boundary habitats. Bird Study, 57, 415-420
- Davey C.M., Vickery J.A., Boatman N.D., Chamberlain D.E., Parry H.R. & Siriwardena G.M. (2010) Assessing the impact of Entry Level Stewardship on lowland farmland birds in England. Ibis, 152, 459-474
- Field R.H., Morris A.J., Grice P.V. & Cooke A.I. (2010) Evaluating the English Higher Level Stewardship scheme for farmland birds. Aspects of Applied Biology, 100, 59-68