Background information and definitions
A 2008 literature review and analysis of the Environmental Stewardship programme, particularly Entry Level Stewardship in the UK (Vickery et al. 2008), suggested that, for Eurasian skylarks Alauda arvensis, approximately 0.1 km² of stubble/km2 would be needed to prevent population declines. The authors also suggest that having these patches over 1 km apart would maximise winter use.
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 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 areas. Abundance on fields under the specific agri-environment schemes increased by 70%, compared with 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 study in the winters of 1997-8 and 1998-9 on 122 stubble fields on 32 farms in central England (Moorcroft et al. 2002) found 13 bird species using stubble fields. Four species (Eurasian linnet Carduelis cannabina, Eurasian skylark Alauda arvensis, reed bunting E. schoeniclus and corn bunting Miliaria calandria) were found more frequently on intensively-farmed barley stubbles than intensive or organic wheat, whilst woodpigeons Columba palumbus were found most frequently on organic wheat.Study and other actions tested
A replicated, randomised study from November 2003 to March 2004 in 205 cereal stubble fields under a range of management intensities in arable farmland in south Devon, UK (Defra 2004), found that barley stubbles following low-input herbicide were more beneficial for cirl buntings Emberiza cirlus than wheat or conventionally managed stubbles. Higher population sizes were also associated with the number of breeding bunting territories the previous season, and with small field size. The effect of small field size may be because cirl buntings prefer to forage near hedgerows and because smaller fields are less intensively managed. The authors argue for strategic spatial targeting of stubble prescriptions. Overall, barley fields were generally preferred by seed-eating species. Low-input barley stubbles had significantly higher seed abundance and broad-leaved weed cover (approximately four times greater). Fields where stubbles were grazed over winter had significantly lower densities of seed-eating birds in general. The authors point out that seed-eating species’ preference for barley stubbles was independent from the positive correlation with broad-leaved weed density and should be taken into account when planning prescriptions.Study and other actions tested
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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 skylarks Alauda arvensis were significantly denser in fields with stubble left over winter than fields with wild bird cover crops or conventional crops. Stubble fields were those in which cereal and oilseed rape stubbles were left over winter. Between 6.2 and 28.3 ha were sampled on each farm annually. This study is discussed in more detail in ‘Plant wild bird cover crops’ and ‘Provide set-aside areas’.Study and other actions tested
A replicated controlled study in winter 2003-2004 on 20 wheat fields from 12 lowland farms in central England (Butler et al. 2005) found that seed-eating songbirds and invertebrate-feeding birds were more abundant on stubble fields cut to 6 cm, whereas skylark Alauda arvensis and partridge Perdix perdix were more abundant on fields with uncut stubble, approximately 14 cm tall (fields were visited six times each for a total of 120 visits. Seed-eaters: 343 individuals were seen on approximately 25 visits to cut fields vs. 89 individuals on 15 visits to control fields; invertebrate-eaters: 623 birds on 17 visits vs. 34 on five visits; skylarks: 557 on 50 visits vs. 814 on 80 visits; partridges: five on two visits vs. 235 on 27 visits). Crows and pigeons showed no response to stubble cutting. Each field was split so that half was cut to approximately 6 cm tall, with the other half left as a control.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 12 farmland bird species analysed were positively associated with the provision of overwinter stubble, set-aside areas (see ‘Provide or retain set-aside areas in farmland’) or wildlife seed mixtures (see ‘Plant wild bird seed or cover mixture’). These were Eurasian skylarks Alauda arvensis (a field-nesting species) and Eurasian 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 sections.Study and other actions tested
A small randomised site comparison study in winter 2004-5 in central England (Whittingham et al. 2006) found that seed-eating songbirds and invertebrate-feeding birds were found at higher density on sections of fields where stubble had been cut short (642 seed-eaters and 1,207 invertebrate-feeders recorded on cut stubble plots vs. 364 and 415 on cut stubble). Eurasian skylarks Alavda arvenis, partridges, pigeons Columba spp., and meadow pipits Anthus pratensis were at higher densities in areas of uncut stubble (241 skylarks, 100 partridges, 37 pigeons and 81 meadow pipits on uncut plots vs. 27, 7, 12 and 9 on cut plots). In addition, skylarks and invertebrate feeders were found at higher densities on scarified (i.e. lightly tilled) sections of fields than control (unscarified) sections (339 skylarks and 1371 invertebrate feeders on scarified plots vs. 241 and 251 on controls). The stubble on one half of each field was cut in the winter of 2004-2005 before the fields were surveyed between December 2004 and March 2005.Study and other actions tested
A 2007 systematic review identified five papers investigating the effect of overwinter stubble provision on farmland bird densities in the UK (Roberts & Pullins 2007). There were significantly higher densities of farmland birds in winter on fields with stubbles than on conventionally managed fields. In particular, there were greater densities of seed-eating songbirds and crows on fields with stubbles than on control fields. The meta-analysis included experiments conducted between 1992 and 2002 from three controlled trials, before-and-after study, and one site comparison study.Study and other actions tested
A 2009 literature review of agri-environment schemes in England (Natural England 2009) found that there was a 146% increase in cirl bunting Emberiza cirlus territory density on land under a Countryside Stewardship Scheme ‘special project’, which (amongst other interventions) increased the amount of weedy overwinter stubbles in the target area between 1992 and 2003. In addition, the national population increased from 319 to nearly 700 pairs over the same period. Generally, the review found high densities of seed-eating songbirds and Eurasian skylarks Alauda arvensis on stubbles and wild bird seed or cover mix (see ‘Plant wild bird seed or cover mixture’), compared to other land uses, and a survey in the winter of 2007-8 found the highest densities of skylarks on stubble fields, compared with other agri-environment schemes options. This review also examines several other interventions, discussed in the relevant sections.Study and other actions tested
A large 2010 site comparison study of the same 2,046 1 km² plots of lowland farmland in England as in (Davey et al. 2010), 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 consistent association between the provision of stubbles and farmland bird numbers. Grey partridge Perdix perdix and tree sparrow Passer montanus were the only two species that showed more positive population change (population increases or smaller decreases relative to other plots) from 2005 to 2008 in the 9 km² and 25 km² areas immediately surrounding plots planted with stubble than in the area surrounding plots without stubbles. The effect of stubbles was small, however, with tree sparrow numbers increasing by 0.05 at the 9 km² scale for each 0.07 km² of stubble and by 0.07 at the 25 km scale for each 0.14 km² of stubble. 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 Entry Level Stewardship or Countryside Stewardship Scheme. In both survey years, two surveys were conducted along a 2 km pre-selected transect route through each 1 km² square.Study and other actions tested
A replicated site comparison study on 1,031 agricultural sites across England in 2004-2008 (Ewald et al. 2010) found that the ratio of young to old grey partridges Perdix perdix on sites was positively related to the proportion of sites left as overwinter stubble. However, when stubbles were used in conjunction with other interventions, the results were mixed. In conjunction with small field sizes and reduced chemical inputs, stubbles were weakly positively correlated with year-on-year changes in partridge density but negatively related to brood size. In conjunction with undersowing spring cereals, stubbles were negatively associated with year on year changes (2006-2007) and overwinter survival (2004-2005, 2005-2006 and generally). This study describes the effects of several other interventions, discussed in the relevant sections.Study and other actions tested
A replicated site comparison study of 75 fields in East Anglia and the West Midlands (Field et al. 2010) found no difference in the number of seed-eating birds or Eurasian skylarks Alauda arvensis on Environmental Stewardship stubbles and non-Environmental Stewardship stubbles. There was also no significant difference in the number of seed-eating birds on stubbles managed under the Higher Level Stewardship (18.0 birds/ha) than in fields managed under the Entry Level Stewardship (8.5 birds/ha). Skylarks, however, were found to be more numerous on Higher Level Stewardship fields (9.3 birds/ha) than ELS fields (1.2 birds/ha). Entry Level Stewardship stubbles prohibited post-harvest herbicide and cultivation until mid-February; Higher Level Stewardship stubbles had the basic Entry Level Stewardship requirements plus reduced herbicide use. Non-ES stubbles were rotational stubbles without restrictions on herbicide or cultivation practices. Seed-eating birds were surveyed on two visits to each site between 1 November 2007 and 29 February 2008.Study and other actions tested
A replicated site comparison study on farms in two English regions (Field et al. 2010) found more seed-eating farmland songbirds on overwinter stubbles managed under Entry Level Stewardship than on non-stewardship stubbles in the West Midlands (average 6 birds/ha on Entry Level Stewardship compared with 2.5 bird/ha on conventionally managed stubble). This difference was not significant for farms in East Anglia (3.5 birds/ha on Entry Level Stewardship stubble compared with 0.7 birds/ha on conventionally managed stubble fields). Overwinter stubble fields in stewardship schemes have restrictions on herbicide use and cultivation times. The survey was carried out in winter 2007-2008 on 27 farms with Higher Level Stewardship, 13 farms with Entry Level Stewardship and 14 with no environmental stewardship, in East Anglia or the West Midlands. The group of birds analysed included tree sparrow Passer montanus and corn bunting Emberiza calandra, but not grey partridge Perdix perdix. More of these birds used overwinter stubbles on Higher Level Stewardship farms than on Entry Level Stewardship farms. There were 5 birds/ha compared to 2 birds/ha on average, on stubble fields in Higher Level Stewardship and Entry Level Stewardship farms respectively.Study and other actions tested