Action: Leave headlands in fields unsprayed (conservation headlands)
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- Three studies from Europe, two replicated, found that conservation headlands were frequently used by some of all of the bird species studied, or were strongly associated with species. A review from the UK found that grey partridge Perdix perdix populations were far larger on farms with conservation headlands and other interventions in place than other farms. Two replicated studies from Europe found that species were not associated with, or were no more abundant on, conservation headlands, compared with control fields.
- All four studies, three replicated, that investigated survival found higher grey partridge Perdix perdix chick or adult survival on sites with conservation headlands than control sites. One found that this difference was not significant.
- Five studies from Europe, four replicated, found larger grey partridge broods on farms with conservation headlands, one study found that differences were not significant. One replicated study from the UK found that fewer broods were found in fields with conservation headlands. Another replicated study from the UK found no relationship between conservation headlands and partridge brood size or young to adult ratio.
Conservation headland management (under European agri-environment schemes) involves restricted fertiliser, herbicide and insecticide spraying in a 6 m margin of sown arable crop. The prescription allows selected herbicide applications to control certain weeds or invasive species.
Supporting evidence from individual studies
A replicated, controlled study of cereal headlands on an arable farm in north-east Hampshire, UK (Rands et al. 1984), found that grey partridge brood size was significantly larger on unsprayed compared to sprayed headlands (6.4 chicks/brood on unsprayed vs. 2.2 on sprayed headlands). Abundance of chick food species (‘true bugs’, caterpillars and sawfly larvae, leaf beetles and weevils) was significantly greater in unsprayed headlands compared to sprayed headlands (180 individuals/50 sweeps for unsprayed vs. 62 for sprayed). Three areas were split into two treatment plots: sprayed with conventional pesticides or 6 m headlands left unsprayed. Grey partridge brood size was recorded from August-September 1983. Insects were sampled using a sweep net (50 sweeps in June).
A replicated, controlled study in 1980-3 in arable fields on a farm in Hampshire, England (Rands 1985) (the same site as in Rands et al. 1984), found that grey partridge Perdix perdix broods were significantly larger in 1983 on plots with conservation headlands, compared to controls, with headlands sprayed with fungicides and herbicides (averages of 5.1-10.3 chicks/brood for 29 broods in unsprayed areas vs. 1.8-2.4 chicks/brood for 39 broods on controls). No differences were found in 1980-1, before conservation headlands were implemented. However, more broods were found on conventional fields, reflecting more pairs (49 vs. 37) in the spring. The author argues that larger broods were the result of higher chick survival, with conservation headland plots contain significantly more food insects than controls.
A replicated, controlled study in 1984 on the same farm as in (Rands et al. 1984, Rands 1985) and on eight sites in East Anglia, England (Rands 1986), found that grey partridge Perdix perdix broods had significantly higher survival, and were significantly larger on plots with conservation headlands, compared to control plots with conventionally-sprayed headlands (average of 75% survival and 7.8-10.0 chicks/brood for five broods on conservation headland plots vs. 60% and 4.7-7.5 chicks/brood for four broods on conventional plots; 196 broods surveyed). This paper also describes similar, although less conclusive effects on two non-native gamebirds.
A paired, replicated, controlled study in the 1980s in cereal fields in southern and eastern England, UK (Sotherton 1991), found that in each year 1983-6, the brood size of grey partridge Perdix perdix and/or pheasant Phasianus colchicus was higher on blocks of cereal fields with conservation headlands (6-10 and 4-7 chicks respectively) compared with normally sprayed headlands (3-8 and 2-3 chicks) (Sotherton & Robertson 1990). Breeding density of grey partridges on the Hampshire farm increased from 4 to 12 pairs/km2 between 1979 and 1986. No such increases were recorded on adjacent farms where pesticide regimes remained unchanged.
A replicated, controlled study of cereal fields on ten pairs of farms in central and southern Sweden (Chiverton 1994) found that grey partridge brood size, chick survival and abundance of invertebrates tended to be higher on farms with unsprayed headlands (6 m wide) compared to those sprayed conventionally. Mean brood size tended to be higher on experimental farms (half headlands unsprayed; 7-9) than on control farms (sprayed; 3-8). Numbers of broods (10-19 vs. 4-16), chick survival rate (26-54% vs 11-47%) and numbers of partridge pairs in the spring (20-30 vs. 15-24) also tended to be higher on experimental farms. However, none of these differences was statistically significant. Mean density of chick food insect groups (Heteroptera, Homoptera, Curculionidae, Chrysomelidae, larvae of Lepidoptera and Tenthredinidae) was significantly higher on unsprayed (25-74) compared to sprayed headlands of wheat (5-32). Farm pairs (control and experimental) were within 5 km of each other and of similar size, cropping and agricultural practice. On the experimental farm, the headlands left unsprayed (50%) were swapped each year (1991-1993). Partridge counts were undertaken in spring and after harvest using dogs to flush birds. Ten invertebrate samples (0.5 m²) were taken from each headland during the first week in July using vacuum-suction.
A replicated, controlled study of arable fields on eight farms in the Netherlands (de Snoo et al. 1994) found that unsprayed field margins had a higher abundance of blue-headed wagtail Motacilla flava flava than sprayed edges. Blue-headed wagtails made 1.5-2.4 visits/km to unsprayed margins compared to just 0.5 visits/km for sprayed margins. Numbers of Eurasian skylarks Alauda arvensis and meadow pipits Anthus pratensis did not differ significantly in sprayed and unsprayed margins (skylark: 0.4 vs. 0.2-0.4; pipits: 0.1 vs. 0.1). Blue-headed wagtails and skylarks visited field margins more than field centres and sprayed edges bordering ditches more than sprayed edges adjacent to a second plot. Strips 6 m wide along field edges were left unsprayed by herbicides and insecticides (total length 2,560-3,790 m/year) and were compared to sprayed edges in the same field and to the sprayed field in 1992-1993. Farmland birds were sampled using a linear transect census, with all birds visiting field margins recorded and a similar size strip in the centre of each field recorded. Birds were sampled 10-12 times between April and mid-July.
A 1998 literature review (Sotherton 1998) found three studies, two in the UK (Rands 1985 and Rands et al. 1986 described above) and one in Sweden, showing that gamebird (grey partridge Perdix perdix) chick survival rates were significantly higher in conservation headlands with reduced pesticide inputs compared to controls receiving the usual pesticide application.
A literature review of studies in the UK (Aebischer et al. 2000) found that the populations of grey partridge Perdix perdix was 600% higher on farms with conservation measures aimed at partridges in place, compared to farms without these measures. Measures included the provision of conservation headlands, planting cover crops, using set-aside and creating beetle banks.
A replicated study in 1999 and 2003 on farms in East Anglia and the West Midlands, England (Stevens & Bradbury 2006), found that five of twelve farmland bird species analysed were positively associated with conservation headlands and a general reduction in herbicide use (see separate intervention). These were corn bunting Miliaria calandra (a field-nesting species) and chaffinch Fringilla coelebs, greenfinch Carduelis chloris, whitethroat Sylvia communis, and yellowhammer Emberiza citrinella (all boundary-nesting species). The study did not distinguish between conservation headlands and a general reduction in herbicide use, classing both as interventions reducing pesticide use. A total of 256 arable and pastoral fields across 84 farms were surveyed. Several other interventions are also analysed and discussed in the relevant sections.
A 2009 literature review of agri-environment schemes in England (Natural England 2009) found evidence (including in studies reviewed in this section) that grey partridge Perdix perdix broods were significantly larger in cereal fields with a 6 m unsprayed margin around them, compared to conventional fields. This review also examines several other interventions, discussed in the relevant sections.
A 2009 literature review of European farmland conservation practices (Vickery et al. 2009) found that gamebirds made frequent use of conservation headlands, for shelter and foraging. The authors note that the effects on non-gamebirds are less certain.
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 overwinter survival was positively correlated with the proportion of a site under conservation headlands in 2007-8, and with year-on-year density changes in 2006-7. There were no relationships with brood size or the ratio of young to old birds. This study describes the effects of several other interventions, discussed in the relevant sections.
- Rands M.R.W., Sotherton N.W. & Moreby S.J. (1984) Some effects of cereal pesticides on gamebirds and other farmland fauna. Recent developments in cereal production. University of Nottingham, December 1984., 98-113.
- Rands M.R.W. (1985) Pesticide use on cereals and the survival of grey partridge chicks: A field experiment. Journal of Applied Ecology, 22, 49-54
- Rands M.R.W. (1986) The survival of gamebird (Galliformes) chicks in relation to pesticide use on cereals. Ibis, 128, 57-64
- Sotherton N.W. (1991) Conservation Headlands: a practical combination of intensive cereal farming and conservation. Pages 373-397 in: L.G. Firbank, N. Carter, J.F. Derbyshire & G.R. Potts (eds.) The Ecology of Temperate Cereal Fields. Blackwell Scientific Publications,
- Chiverton P.A. (1994) Large-scale field trials with conservation headlands in Sweden. British Crop Protection Council Monographs, 58, 185-190
- de Snoo G.R., Dobbelstein R. & Koelewijn S. (1994) Effects of unsprayed crop edges on farmland birds. British Crop Protection Council Monographs, 58, 221-226
- Sotherton N. (1998) Land use changes and the decline of farmland wildlife: an appraisal of the set-aside approach. Biological conservation, 83, 259-268
- 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.
- 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
- Natural England (2009) Agri-environment schemes in England 2009: A review of results and effectiveness (NE194). Natural England report.
- Vickery J.A., Feber R.E. & Fuller R.J. (2009) Arable field margins managed for biodiversity conservation: a review of food resource provision for farmland birds. Agriculture, Ecosystems & Environment, 133, 1-13
- 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