Background information and definitions
Allocation of some farmland to ‘set-aside’ (fields taken out of production) was compulsory under European agricultural policy from 1992 until 2008. Originally intended as a method of reducing production, set-aside has also been promoted as a way of protecting on-field biodiversity. Set-aside fields can be sown with fallow crops or left to naturally regenerate. Set-aside can be rotational (in a different place every year) or long term (retained for 5–20 years).
A 2008 literature review of the Environmental Stewardship programme, particularly Entry Level Stewardship (ELS) in the UK (Vickery et al. 2008) found that the population trends of all Farmland Bird Index species were positively correlated with the availability of set-aside in that year and that Entry Level Stewardship may not be able to effectively replace set-aside.
Vickery, J., Chamberlain, D., Evans, A., Ewing, S., Boatman, N., Pietravalle, S., Norris, K. & Butler, S. (2008) Predicting the impact of future agricultural change and uptake of Entry Level Stewardship on farmland birds. British Trust for Ornithology, The Nunnery, Thetford.
Supporting evidence from individual studies
A replicated, paired sites study on seven pairs of fields in northeast Scotland in 1989-91 (Watson & Rae 1997) found that one-year-old set-aside fields held significantly more species of bird than similar, non-set-aside fields (average of 12 species/10 ha for first year set-aside vs. 5 species/10 ha for ‘control’ fields). There were no differences in the years before or after set-aside. In addition, there were higher breeding densities of grey partridge Perdix perdix, Eurasian skylark and Eurasian curlew Numenius arquata in set-aside compared with ‘control’ fields. Densities of curlew, partridge, northern lapwing Vanellus vanellus and Eurasian oystercatcher Haematopus ostralegus were higher in set-aside years than before set-aside (songbird densities were not recorded before set-aside was used). Wader breeding success appeared higher on set-aside, but numbers were too small for statistical tests. The densities and number of species declined over time in set-aside fields. Set-aside fields were previously arable fields but were not cropped for at least one year.Study and other actions tested
A replicated study in summers of 1993-95 on seven farms in southern England (Wilson et al. 1997) found that there were significantly higher densities of Eurasian skylark Alauda arvensis nests on set-aside fields than on conventionally or organically managed crop fields (0.3-0.5 territories/ha for set-aside fields vs. a maximum of 0.4 territories/ha for cropped fields). Estimated nest survival was significantly higher on set-aside fields than conventionally managed cereal fields (44% survival to fledgling on set-aside vs. 11% for conventional cereals). Set-aside was either naturally regenerated from crop stubble or sown with grass.Study and other actions tested
A site comparison in April to August 1992 on three farms in south England (Poulsen et al. 1998) found that skylarks had significantly higher productivity in set-aside fields, compared to spring-sown cereals or grass (0.5 fledglings/ha in set-aside vs. 0.21 fledglings/ha in spring cereals and 0.1 fledglings/ha in silage grass). This difference was largely due to higher densities of territories (2-3 times higher in set-aside and grass, compared to cereals) and more successful nests (highest on grass, but twice as high in set-aside as in cereal crops) and larger clutches in set-aside (3.9 eggs/clutch for nests in set-aside vs. 3.3 eggs/clutch for spring cereals and 3.4 eggs/clutch in grass, eleven nests in each habitat type). Fledging success did not vary between habitats. No nests with chicks were found in winter-sown cereals. Set-aside consisted of four year-old permanent fallow sown with red fescue Festuca rubra, perenial rye-grass Lolium perenne and white clover Trifolium pratense.Study and other actions tested
A replicated study in summer 1995 on 89 fields in the South Downs, southern England (Wakeham-Dawson et al. 1998 ), found that the density of singing Eurasian skylarks was higher on set-aside fields than on any other field type, except undersown spring barley fields (approximately 15 birds/km2 on six set-aside fields vs. 22 birds/km2 on four spring barley fields and 2-12 birds/km2 on 79 other fields). Other field types were arable fields reverted to species-rich grassland (‘Habitat restoration and creation’) or permanent grassland (Revert arable land to permanent grassland’); downland turf (close-cropped, nutrient-poor grassland); permanent grasslands; and winter wheat, barley and oil seed rape. This study is also described in ‘Reduce grazing intensity on permanent grasslands’ and ‘Undersow spring cereals’.Study and other actions tested
A randomised and replicated site comparison in the winters of 1992-1993 and 1993-1994 on 40 farmland sites in Devon and East Anglia, UK (Buckingham et al. 1999) found that only one taxonomic group (finches, sparrows and buntings, seven species) showed a significant preference for set-aside habitats in both years, preferentially using sown set-aside less than one year old. Conversely, thrushes (four species) and hedge-dwelling species (European robin Erithacus rubecula, wren Troglodytes troglodytes and dunnock Prunella modularis) avoided regenerating set-aside less than one year old in Devon. At a species level, a preference for set-aside was seen in both winters by one species in Devon (cirl buntings Emberiza cirlus selecting sown set-aside more than one year-old) and two species (plus one introduced species not considered here) in East Anglia (grey partridge preferred older sown set-aside and yellowhammer Emberiza citrinella selected one year-old sown cover). A further 13 species in both East Anglia and Devon preferentially selected a set-aside habitat in one winter. Blackbirds Turdus merula and five other species avoided some set-aside in at least one year in Devon; no native species did so in East Anglia. The same 40 plots (50-100 ha) were surveyed each winter, although the amount of set-aside they contained varied due to rotation schemes.Study and other actions tested
A 2000 literature review from the UK (Aebischer et al. 2000) found that the populations of grey partridge, Eurasian thick-knee Burhinus oedicnemus and cirl buntings all increased following multiple measures including the provision of set-aside. Partridge numbers were 600% higher on farms with conservation measures aimed at partridges (including conservation headlands, planting cover crops, using set-aside and creating beetle banks) in place, compared to farms without these measures; the UK thick-knee population increased from 150 to 233 pairs from 1991 to 1999 (interventions were set-aside provision and uncultivated plots in fields); the UK cirl bunting population increased from 118-132 pairs in 1989 to 453 pairs in 1998, with a 70% increase on fields under schemes (with overwinter stubbles, grass margins, and beneficially managed hedges and set-aside), compared to a 2% increase elsewhere.Study and other actions tested
Referenced paperAebischer 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.
A replicated paired sites study in 1996-7 across 92 arable farms in England (Henderson et al. 2000) found that five of six bird functional groups examined were at higher densities on set-aside fields, compared to winter cereals or grassland (although thrushes only showed this preference in one year). On ten farms with rotational and non-rotational set-aside, all groups except crows were found at higher densities on rotational set-aside fields. All groups except gamebirds (which showed no significant field preferences) were also more likely to be found on set-aside than on other field types. Functional groups of birds were gamebirds, pigeons, crows, skylarks, thrushes and seed-eating songbirds (sparrows, buntings and finches).Study and other actions tested
A replicated paired sites study in 1996-7 on 11 farms in east and west England (Henderson et al. 2000), found that set-aside fields supported more species and higher densities of birds than adjacent crop fields (1-7 birds/ha and 7-21 species for 11 set-aside fields vs. 0.2-0.8 birds/ha and 2-5 species on 11 crop fields). Between 78% and 100% of species found on both field types were more abundant on set-aside. These preferences were stronger (although not significantly so) for rotational set-aside, compared to non-rotational.Study and other actions tested
Another analysis (Henderson et al. 2001) as part of the same study as in Henderson et al. (2000) found that skylark densities on set-aside fields ranged from zero to approximately three birds/ha. A total of 74 set-aside fields (36 rotational and 38 non-rotational) were examined, each from a different farm. The authors’ note that fields with approximately 30% bare earth, straw and litter had the highest densities of skylarks.Study and other actions tested
A replicated study in 1996-98 on 22 farms in southern England (Donald et al. 2002) found that skylark nests had significantly lower survival in set-aside, compared to in cereals (22% overall survival for 525 nests in set-aside vs. 38% survival for 183 nests in cereal fields). There were no differences between set-aside and other crop types (19% survival for 173 nests in grass fields, 29% survival for 60 nests in other field types) or between rotational and non-rotational set-aside. On one intensively-studied farm, over 90% of 422 skylark nests were found on ten fields of well-established, non-rotational set-aside. This study also describes the impact of predator control on skylark nest survival, discussed in ‘Control predators not on islands ‘.Study and other actions tested
A study of different set-aside crops at Allerton Research and Educational Trust Loddington farm, UK (Murray et al. 2002) found that Eurasian skylark, but not yellowhammer Emberiza citronella, used unmanaged set-aside more than expected compared to availability. Skylarks used unmanaged set-aside more than expected compared to availability, but significantly less than kale set-aside ‘wild bird cover’, ‘wild bird cover’ strips and beetle banks. Cereal (wheat, barley) and broad-leaved crops (beans, rape) were used less than expected. Yellowhammer used unmanaged set-aside as expected compared to availability and used it significantly less than cereal and cereal set-aside ‘wild bird cover’ and ‘wild bird cover’ strips. Set-aside strips (field margin and midfield) were sown with kale-based and cereal-based mixtures for ‘wild bird cover’ and ‘beetle banks’. Other habitat types were: unmanaged set-aside, cereal (wheat, barley), broad-leaved crop (beans, rape) and ‘other’ habitats (including permanent pasture, woodland, hedgerows, tracks and riparian areas). Thirteen skylark and 15 yellowhammer nests with chicks between 3-10 days old were observed. Foraging habitat used by the adults was recorded for 90 minutes during three periods of the day. This study is also discussed in ‘Create beetle banks’ and ‘Plant wild bird seed /cover’.Study and other actions tested
A replicated, randomised study of 200 farms in England with set-aside (Firbank et al. 2003) found that an increase in bird numbers was reported by 47% of farmers with rotational set-aside and 69% of farmers with non-rotational set-aside. Bird density in rotational set-aside was nine times, and in non-rotational sown grassland set-aside seven times, that in crops. Management of set-aside had minimal effect on bird abundance. Breeding bird territories were mapped on 63-92 farms (1996-1997). More intensive surveys were undertaken for habitat use by birds on 11 farms (1996-1997).Study and other actions tested
A meta-analysis of 127 studies comparing set-aside and conventional land (Van Buskirk & Willi 2004) found that species richness and population densities of birds were significantly higher on set-aside land than on nearby conventional fields in Europe and North America. Positive effects were greatest on larger and older areas of set-aside, when the comparison conventional field was crops rather than grasses and in countries with more arable land under agri-environment schemes and with less intensive agriculture. Overall, variation in establishment methods and types of set-aside made little difference to the positive effect on biodiversity, although species richness was increased more when set-aside was naturally regenerated rather than sown.Study and other actions tested
A replicated, randomised, controlled study from November-February in 2000/2001 and 2001/2002 in 20 arable farms in eastern Scotland (Parish & Sotherton 2004) found that, of 23 species recorded, only Eurasian skylarks were found at higher densities in fields with set-aside than fields with wild bird cover crops or conventional crops. Bird density was up to 100 times greater in wild bird cover crops than on set-aside fields. The wild bird cover crops attracted 50% more species than set-aside fields. Of eight species with sufficient data for individual analysis, seven were consistently significantly more abundant in wild bird cover than in set-aside fields. Set-aside fields were those in which cereal stubble was left to regenerate naturally. Between 6 and 28 ha were sampled on each farm annually.Study and other actions tested
A replicated paired sites comparison in summer 2003 in County Laois and County Kildare, Ireland (Bracken & Bolger 2006), found that 18 set-aside fields had significantly higher avian species diversity and richness than 18 adjacent agricultural fields (an average of 13 species on set-aside vs. 9 species on farmed fields). Three species were significantly more abundant on set-aside and whilst six species showed a preference for non-set-aside fields, these preferences were not significant and the species (whitethroat Sylvia communis, goldcrest Regulus regulus, blackcap Sylvia atricapilla, stonechat Saxicola torquata, tree sparrow Passer montanus and treecreeper Certhia familiaris) were more likely to be selecting habitats based on field margins, rather than field management. Six species were associated with non-rotational set-aside; two with rotational set-aside; one with long-term grazed pasture set-aside and three with first year pasture set-aside.Study and other actions tested
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 only two of twelve farmland bird species analysed were positively associated with the provision of set-aside, wildlife seed mixtures (see ‘Plant wild bird seed or cover mix’) or overwinter stubble (see ‘Leave overwinter stubbles’). These were skylarks Alauda arvensis (a field-nesting species) and linnets Carduelis cannabina (a boundary-nesting species). The study did not distinguish between set-aside, wildlife seed mixtures or overwinter stubble, classing all as interventions to provide seeds for farmland birds. This study describes several other interventions, discussed in the relevant section.Study and other actions tested
A 2007 systematic review identified 11 papers investigating the effect of set-aside provision on farmland bird densities in the UK (Roberts & Pullin 2007). In both winter and summer surveys there were significantly higher densities of farmland birds on fields removed from production and under set-aside designation than on conventionally farmed fields. The meta-analysis included experiments conducted between 1988 and 2002 from eight controlled trials and three site comparison studies.Study and other actions tested
A before-and-after study, examining data from 1976-2003 from farms across southern Sweden (Wretenberg et al. 2007) found that four locally migrant farmland birds showed less negative (or positive) population trends during a period of agricultural extensification, which included an increase in the area of set-aside. The authors suggest that the two could be causally linked. This study is discussed in ‘Pay farmers to cover the costs of conservation measures’.Study and other actions tested
A before-and-after site comparison study in 2000-2005 in Bedfordshire, England (Henderson et al. 2009), found that set-aside fields sprayed in May or June supported higher densities of grey partridge, seed-eating songbirds and skylarks Alauda arvensis, compared to set-aside sprayed in April or crop fields (although seed-eating passerines were equally numerous on oilseed rape Brassica napus fields). Early-sprayed set-aside had consistently lower densities of all species, compared to all land uses except winter-sown wheat. The site-level effects of set-aside and sowing crops in spring are discussed in ‘Sow crops in spring, not autumn’. This study also investigated the impact of reducing pesticide and fertiliser inputs.Study and other actions tested
A controlled study in 2002- 2009 on mixed farmland in Hertfordshire, England (Aebischer & Ewald 2010), found that the estimated population density of grey partridges Perdix perdix was significantly higher on set-aside land, than on conventional arable crops. The difference was strongest for rotational set-aside, with non-rotational set-aside not having a significant positive impact on partridge densities. This study also examined the densities found on land under various agri-environment schemes (which were similar to those on set-aside, see ‘Pay farmers to cover the costs of conservation measures’), wild bird cover (which were higher than those on set-aside, see ‘Plant wild bird seed or cover mixture’) and the impact of predator control and supplementary food provision (see ‘Provide supplementary food to increase adult survival’ and ‘Control predators not on islands’).Study and other actions tested
A small study on four farms in Aberdeenshire, north east Scotland, in summer 2005 (Douglas et al. 2010) found that yellowhammers from ten nests preferentially foraged on set-aside land, compared to cereal fields, but that this preference was not significant (set-aside comprising 23% of available habitat but used for 42% of foraging flights vs. cereals comprising 42% of habitat and being used 25% of the time).Study and other actions tested
A study in April-May 2004 and 2005 (Mcmahon et al. 2010), found that four birds of conservation concern were all found on set-aside on 210 fields in pseudo-steppe farmland in Catalonia, Spain. Little bustards Tetrax tetrax were found on 23-50% of fields within their range at densities of 0.3-0.8 birds/ha (68 fields surveyed in 2004, 86 in 2005), Eurasian thick-knee on 43-52% at 0.4-0.6 birds/ha (93 fields in 2004, 117 in 2005), short-toed larks Calandrella brachydactyla on 28-32% at 0.2-0.4 birds/ha (50 fields in 2004, 64 in 2005) and calandra larks Melanocorphya calandra on 27-34% at 0.4-0.7 birds/ha (93 fields in 2004, 117 in 2005). Only male bustards were recorded, due to problems surveying cryptic females.Study and other actions tested