Action: Plant grass buffer strips/margins around arable or pasture fields for birds
- One replicated controlled study from the USA found that there were more species in fields bordered by margins than unbordered fields. Two replicated studies from the UK, one with paired sites, found no effect of field margins on species richness. A replicated, controlled study from the UK found that more birds and more species used sown strips in fields than the fields themselves, but even more used field margins.
- Nine studies from the UK and USA, seven replicated, two controlled, found more positive population trends, higher populations or strong habitat associations for some or all species for sites with grass margins to fields. One study investigated multiple interventions. Three replicated studies from the UK found that grass field margins did not have a positive effect on populations of some or all bird species investigated.
- Both studies that examined habitat use (one replicated, both from the UK) found that species used margins more than other habitats. A randomised, replicated and controlled study from the UK found that birds used cut margins more than uncut margins during winter but less than other management regimes during summer. The authors argue that management type is more important than the seed mix used to sow the margins.
- A replicated study from the UK found that grey partridge Perdix perdix had smaller broods in grass margins than other habitat types.
This intervention involves planting field margins with a grass-rich seed mixture. It includes ‘floristically-enhanced' grass margins available under the English Higher Level Stewardship scheme. The margins are not fertilised and only spot-treated with herbicides if necessary.
Supporting evidence from individual studies
A replicated, controlled study in summer and autumn of 1995 and 1996 on 15 sown set-aside strips on a farm in Cambridgeshire, UK (Clarke et al. 1997) found that more bird individuals (average 20%) and species (average 56%) used the strips than the adjacent crop area (average 7% individuals and 33% species) in both years. However, the highest proportions of both individuals and species were recorded in the field boundaries (average 68% ind. and 80% spp.). The highest species richness was found in the most diverse grass mix. The seed mixture ‘Tübinger Mischung’ with only wildflowers attracted most individuals, but the lowest species numbers. Note that no statistical analyses were performed on these data. Five seed mixtures were sown on set-aside areas (minimum 20 m wide and 100 m long) in the autumns of 1993 and 1994. Seed mixtures contained either only grass species (three mixes including three to six species, cost £15-£70/ha), a mix of grasses and herbs (six grass and eight herb species, cost £300/ha) or only herbs 11 species, £35/ha). Birds were recorded during 15 min point counts on 10 occasions between June and September 1995 and July and October 1996. Each bird’s location was recorded in three categories: field boundary, set-aside strip and crop. After each count, the strips were walked to flush any birds present but not visible during the count.
A 2000 literature review (Aebischer et al. 2000) found that the UK population of cirl buntings 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-environment scheme increased by 70%, compared with a 2% increase elsewhere.
A 2001 replicated paired site comparison study in south Devon (Peach et al. 2001) found that fields with 6 m grass margin were associated with increases in cirl bunting Emberiza cirlus numbers. Six of 7 Countryside Stewardship Scheme plots that had 6 m grass margins and were within 2.5 km of former bunting territories gained birds, whereas more generally there were declines of 20% in bunting numbers on land not-participating within the CSS. Forty-one 2x2 km² squares containing both land within Countryside Stewardship Scheme and non-Countryside Stewardship Schemeland were surveyed in 1992, 1998 and 1999. In each year each square was surveyed at least twice, the first time during mid-April to late May, and the second time between early June and the end of August.
A replicated, controlled study in winter 1999/2000 and summer 2000 on 23 pastoral farms in the West Midlands, UK (Buckingham et al. 2002), found 16 times higher winter densities of seed-eating birds within 6 m of boundaries on fields with Countryside Stewardship Scheme grass margins than on fields without (1.1 vs. 0.1 birds/ha), and twice as many Eurasian blackbirds Turdus merula near the boundaries on fields without Countryside Stewardship Scheme grass margins than with (1.8 vs. 0.9 birds/ha). A total of 388 grass fields were surveyed four times each in winter and in summer. No statistical analysis was performed.
A controlled study from May-August in 1995-7 and 1999 on a mixed arable and pastoral farm in Oxfordshire, UK (Perkins et al. 2002), found that yellowhammers Emberiza citronella spent significantly greater time foraging in grass margins and field boundaries than in other habitats. There was no difference between margins and boundaries, or between cut and uncut grass margins. However, greater use was made of both cut and uncut grass margins combined than field boundaries. Habitats surveyed were cut (1.8 km) or uncut (1.6 km) grass margins (2 or 10 m wide, at edges of arable field), field boundaries, arable fields (winter-sown cereals) and grass fields (pasture, silage and hay) found. Total area surveyed was 143 ha in 1995-7 and 107 ha in 1999.
A 2006 replicated site comparison study of 42 fields in the UK (Kleijn et al. 2006) found that installing 6 m-wide grass field margin strips along arable fields had no effect on the number of birds or bird species found to breed or forage on farmland. Under the Countryside Stewardship Scheme, these 6-m-wide grass field margin strips were grown through natural regeneration, the sowing of grass, or grass/forbs mixture. Pesticides applications were prohibited – except for the patch-wise control of problem weeds. The margin, which could not be used for regular access by farm vehicles, may havebe mown once a year after mid July, and dense cuttings must be removed. The study surveyed seven pairs of fields (one with field margins managed under the Countryside Stewardship Scheme, one conventionally farmed) and the 12.5 ha area surrounding each field, from three different regions of the UK four times during the breeding season.
A replicated, paired sites comparison in mid-summer 2003 on 42 arable fields in southern England (Marshall et al. 2006) found that there were no more farmland bird species and birds were no more abundant on fields with 6 m wide grassy margins, compared to control fields without margins (11-18 species/site for 21 fields with margins vs. 11-15 species/site for 21 without).
A replicated study in 1999 and 2003 on 256 arable and pastoral fields across 84 farms in East Anglia and the West Midlands, England (Stevens & Bradbury 2006), found that a combination of creating uncultivated (see ‘Create uncultivated margins around intensive arable or pasture fields’) and planted margins around fields was strongly positively associated with four out of 12 farmland bird species analysed. These were skylarks Alauda arvensis (a field-nesting species) and chaffinches Fringilla coelebs, whitethroats Sylvia communis and yellowhammers Emberiza citrinella (all boundary-nesting species). The study did not distinguish between uncultivated and planted margins. This study describes several other interventions, discussed in ‘Leave headlands in fields unsprayed (conservation headlands)’; ‘Create beetle banks’; ‘Leave uncropped, cultivated margins or plots, including lapwing and stone curlew plots’; ‘Leave overwinter stubbles’; ‘Plant wild bird seed or cover mixture’; ‘Provide or retain set-aside areas in farmland’; ‘Pay farmers to cover the costs of conservation measures’; ‘Reduce pesticide or herbicide use generally’.
A randomised, replicated, controlled trial of sown grassy field margins from 2002 to 2006 in eastern England (Henderson et al. 2007) found that the management of margins affect bird use more than the seed mix used. The number of birds using margins on two farms in summer increased by 29% between 2003 and 2006 and bird densities were higher on disturbed and plots treated with grass-killing herbicides (graminicides) than on cut plots (no actual bird densities given, only model results). Bird densities were linked to densities of diurnal ground beetles (Carabidae), especially in disturbed and graminicide-treated plots. In winter, there were twice as many birds on cut margins on 10 farms as on uncut margins, and twice as many birds in the second year than the first. Field margin plots (6 x 30 m) were established using one of three seed mixes: 1) Countryside Stewardship mix, 2) tussock grass mix and 3) a mixture of grasses and forbs designed for pollinating insects. The margins were managed in spring from 2003 to 2005 with one of three treatments: 1) cut to 15 cm, 2) soil disturbed by scarification until 60% of the area was bare ground, 3) treated with graminicide at half the recommended rate. There were five replicates of each treatment combination, at two farms - one in Boxworth, Cambridgeshire, England, and High Mowthorpe, Yorkshire, England. Birds were surveyed five to eight times between April and July from 2002 to 2006. In winters of 2004/5 and 2005/6, birds were also surveyed on 6 m margins on 10 farms in eastern England with two seed mixes (tussocky grass and fine grass). Margins were either cut in autumn or uncut. There were four replicates of each treatment combination per farm.
A 2007 literature review discussing research on a farm in Leicestershire, UK (Stoate & Moorcroft 2007), found that grass margins around fields contained high numbers of yellowhammer Emberiza citrinella and whitethroat Sylvia communis nests, the former of which had higher survival than in adjacent hedgerows. This study is also discussed in ‘Leave uncropped, cultivated margins or plots, including lapwing and stone curlew plots’, ‘Create skylark plots’ and ‘Create beetle banks’.
A replicated controlled study in May and June 2003-4 on six arable farms in Mississippi, USA (Conover et al. 2009), found that there were significantly more farmland bird species in bordered field margins, compared to unbordered margins (approximately 5 species/ha for 35 bordered margins vs. 0.5 species/ha for 21 unbordered margins). There were higher densities of farmland birds on margins and crops for fields with wide borders (35 birds/ha for 7-11 wide borders and 27-29 birds/ha for adjacent cropland), compared with narrow margins (18 birds/ha for 24-27 narrow borders and 13-15 birds/ha for cropland) or fields without borders (3 birds/ha for 21 unbordered margins and 1-9 birds/ha for cropland). Four species (red-winged blackbird Agelaius phoeniceus, dickcissel Spiza americana, northern cardinal Cardinalis cardinalis, indigo bunting Passerina cyanea) were significantly more abundant on bordered margins. Borders consisted of strips either 6-12 m (narrow) or 20-56 m (wide) around arable fields and planted in spring 2002 with grasses and legumes. If non-native species were dominant, the borders were also treated with selective herbicide.
A replicated study in Aberdeenshire, Scotland, in May-August 2004-6 (Douglas et al. 2009), investigated the impact of cutting sown and naturally regenerated field margins, with yellowhammers Emberiza citrinella appearing to use cut patches of margins for 3% (of 172) in early summer, compared to 34% (of 77) foraging flights in late summer. This study is discussed in ‘Create uncultivated margins around intensive arable or pasture fields’.
A replicated study in February 2008 across 97 1 km2 plots in East Anglia, England (Davey et al. 2010), found that 19 of 24 farmland bird species responded positively to field margins managed under agri-environment schemes, but only yellowhammer Emberiza citrinella and possibly blackcaps Sylvia altricapilla showed strong responses. Great tits Parus major and common starlings Sturnus vulgaris showed weak positive responses. Field margins were categorised as grassy/weedy, bare/fallow or wild-bird cover (although very few fields had wild bird cover) and most were managed under the Entry Level Stewardship scheme. This study also investigated the effects of field boundary management; see ‘Manage hedges to benefit wildlife’.
A replicated site comparison study on 1,031 agricultural sites across England in 2004-8 (Ewald et al. 2010) found that grey partridge Perdix perdix brood size was negatively associated with the proportion of a site under planted grass buffer strips, with a significant relationship in 2008. The ratio of young partridges to old was negatively related to the proportion of grass strips in 2005 and 2008. However, year-on-year changes in partridge density and overwinter survival were positively correlated with the proportion of grass buffer strips on a site in some years - 2006 to 2007 (year-on-year changes) and 2005-6 (overwinter survival). This study describes the effects of several other interventions, discussed in the relevant sections.
A replicated site comparison study on farms in three English regions (Field et al. 2010) found that hedges alongside grass field margins ‘floristically enhanced’ under Higher Level Stewardship had more yellowhammers (estimate of 0.4 birds/m) compared to hedges without a grass margin (estimated 0.2 birds/m). Hedges alongside unenhanced grass margins, either conventionally managed or managed under Entry Level Stewardship, did not have more yellowhammers. Surveys were carried out on 69 farms with Higher Level Stewardship in East Anglia, the West Midlands or the Cotswolds and on 31 farms across all three regions with no environmental stewardship.
- Clarke J.H., Jones N.E., Hill D.A. & Tucker G.M. (1997) The management of set-aside within a farm and its impact on birds. Proceedings - Brighton Crop Protection Conference, Brighton, 1, 1179-1184.
- 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.
- Peach W., Lovett L., Wotton S. & Jeffs C. (2001) Countryside stewardship delivers cirl buntings (Emberiza cirlus) in Devon, UK. Biological Conservation, 101, 361-373
- Buckingham D.L., Peach W.J. & Fox D. (2002) Factors influencing bird use in different pastoral systems. Proceedings of the British Grassland Society/British Ecological Society Conference, University of Lancaster, 15-17 April, 2002, 55-58.
- Perkins A.J., Whittingham M.J., Morris A.J. & Bradbury R.B. (2002) Use of field margins by foraging yellowhammers Emberiza citrinella. Agriculture, Ecosystems & Environment, 93, 413-420
- Kleijn D., Baquero R.A., Clough Y., Diaz M., De Esteban J., Fernandez F., Gabriel D., Herzog F., Holzschuh A., Johl R., Knop E., Kruess A., Marshall E.J.P., Steffan-Dewenter I., Tscharntke T., Verhulst J., West T.M. & Yela J.L. (2006) Mixed biodiversity benefits of agri-environment schemes in five European countries. Ecology Letters, 9, 243-254
- Marshall E.J.P., West T.M. & Kleijn D. (2006) Impacts of an agri-environment field margin prescription on the flora and fauna of arable farmland in different landscapes. Agriculture, Ecosystems & Environment, 113, 36-44
- Stevens D.K. & Bradbury R.B. (2006) Effects of the Arable Stewardship Pilot Scheme on breeding birds at field and farm-scales. Agriculture, Ecosystems & Environment, 112, 283-290
- Henderson I.G., Morris A.J., Westbury D.B., Woodcock B.A., Potts S.G., Ramsay A. & Coombes R. (2007) Effects of field margin management on bird distributions around cereal fields. Aspects of Applied Biology, 81, 53-60
- Stoate C. & Moorcroft D. (2007) Research-based conservation at the farm scale: development and assessment of agri-environment scheme options. Aspects of Applied Biology, 81, 161-168
- Conover R.R., Burger L.W. Jr. & Linder E.T. (2009) Breeding bird response to field border presence and width. Wilson Journal of Ornithology, 121, 548-555
- Douglas D.J.T., Vickery J.A. & Benton T.G. (2009) Improving the value of field margins as foraging habitat for farmland birds. Journal of Applied Ecology, 46, 353-362
- 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
- Ewald J.A., Aebischer N.J., Richardson S.M., Grice P.V. & Cooke A.I. (2010) The effect of agri-environment schemes on grey partridges at the farm level in England. Agriculture, Ecosystems & Environment, 138, 55-63
- 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