Action: Plant wild bird seed or cover mixture
- All seven studies (based on five replicated experiments and a review) that investigated species richness or diversity were from the UK and found that fields or farms with wild bird cover had higher bird diversity than those without, or that more species were found in wild bird cover than in surrounding habitats.
- Thirty-two studies out of 33 from the UK and North America that examined abundance and population data, found that bird densities, abundances, nesting densities or use of wild bird cover was higher than in other habitats or management regimes, or that sites with wild bird cover had higher populations than those without. These studies included a systematic review and seven randomised, replicated and controlled studies. Some studies found that this was the case across all species or all species studied, while others found that only a subset showed a preference. Four studies investigated other interventions at the same time. Thirteen of the 33 studies (all replicated and from Europe and the USA), found that bird populations or densities were similar on wild bird cover and other habitats, that some species were not associated with wild bird cover or that birds rarely used wild bird cover.
- Three studies from the UK and Canada, two replicated, found higher productivities for some or all species monitored on wild bird cover, compared to other habitats. Two replicated and controlled studies from Canada and France found no differences in reproductive success between wild bird cover and other habitats for some or all species studied.
- Three studies from Europe and the USA investigated survival, with two finding higher survival of grey partridge Perdix perdix released on wild bird cover or of artificial nests in some cover crops. The third found that survival of grey partridge was lower on farms with wild bird cover, possibly due to high predation.
- Five studies from the UK, three replicated, found that some wild bird cover crops were preferred to others. A randomised, replicated and controlled study and a review from the UK found that the landscape surrounding wild bird cover and their configuration within it affected use by birds.
The loss of food supplies, especially seeds, is thought to be a key driver of farmland bird declines. Plants that provide seed food for wild birds include maize, sunflower and cereals. They can be planted in blocks or 6 m wide strips and are left unharvested. These plants can also provide cover for nesting birds or juveniles and are sometimes called wild bird cover, ‘game crops’ or ‘game cover crops’.
Supporting evidence from individual studies
A replicated, controlled study from May-June in 1955-1958 in three treatment cover types and six natural (control) cover types in Idaho, USA (Jones & Hungerford 1972), found that artificial nests in some cover crops were less likely to be predated than those in other crops. Over ten days, 30% of nests in cereal crops or cattail Typha angustifolia, bulrush Scirpuss acutus or S. validus margins were predated, compared with 40% in alfalfa Medicago sativa and 80% in tall weeds, willows Salix spp., sagebrush Artemisia tridentate or downy chess Bromus tectorum. Overall, 52% of nests were destroyed within 10 days. Grain fields provided significantly greater protection (average ten ‘safe’ days and only 3% nests destroyed) compared to alfalfa and irrigation ditches (average of seven and five ‘safe’ days) or any control cover types. A total of 529 nests, each containing four eggs were placed randomly in cover types (32-68 nests/cover type).
A study of habitat use by yellowhammers Emberiza citronella on a mixed farm in Leicestershire, UK (Stoate & Szczur 1997) found that in summer yellowhammers used both cropped and uncropped habitats including Wild Bird Cover, whereas in winter Wild Bird Cover was used more than all other habitats relative to its availability. In summer, Wild Bird Cover strips (8 m wide) were used significantly more than wheat or field boundaries (2 m wide), but less than barley. In winter, cereal-based Wild Bird Cover was used significantly more than all other habitats and kale-based Bird Cover was used significantly more than cereal and rape crops. A 15% area of the arable land was managed for game birds. Yellowhammer nests were observed for 1.5-2 hours when nestlings were 4-10 days old and 5-15 foraging sorties per nest were plotted during May-June 1993 and 1995. A 60 ha area of the farm was also walked seven times in November-December and February-March 1997 and habitat use was recorded.
A replicated, controlled study in May-July 1992-94 of 31 wild bird cover and 31 control prairie-parkland plots in Saskatchewan, Canada (McKinnon & Duncan 1999) found that mallard Anas platyrhyncos and gadwall A. strepera displayed higher nest survival rates in wild bird cover than in unmanaged plots (14-16% vs. 4%). There was no difference in nest survival for blue-winged teal A. discors and northern shoveler A. clypeata nests (10-15% vs. 10-14%). Nest survival rates differed significantly between years (8-26% in wild bird cover and 4-16% in control plots) and overall nesting density in wild bird cover plots was low (1.1-1.4 nests/ha). Consequently, the authors suggest that wild bird cover plots would need prohibitively large areas of establishment to be effective. The wild bird cover plots were planted on previously cultivated land with a grass-legume mix (average 37 ha); unmanaged plots were cropland (average 40.4 ha).
A 2000 literature review from 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 small study of set-aside strips over five years at Loddington, Leicestershire, UK (Boatman & Bence 2000), found that set-aside sown with wild bird cover was used by nesting Eurasian skylarks Alauda arvensis significantly more than other habitats. The majority of skylark territories found were within set-aside strips (margins or midfield) sown with wild bird cover (55-76% each year), although the habitat covered only 8-10% of the area. The habitat was also used more for foraging than all others, except linseed. Wild bird cover was sown with either cereal-based or kale-based mixtures. Skylark territories were recorded in 1995-1997 and 1999. Nests were located in 1999 and foraging trips observed for two one and a half hour periods.
A small before-and-after study from May-July in 1992-1994 in river islands in Quebec, Canada (Lapointe et al. 2000), found that the number of dabbling ducks Anas spp. nesting in the study area increased from 143 to 263 nests, following the establishment of dense nesting cover and rotational grazing (see ‘Graze semi-natural habitats’). Density of nests on fields seeded with dense nesting cover in 1993 as higher than other habitats in 1994 (7 nests/ha vs. 1.1-2.8 nests/ha for other habitats). Nesting success in seeded fields was also higher (82% success for 64 nests) than in improved pastures (15% for 39 nests).
A replicated, randomised study of annual and biennial crops over three years in Norfolk, Hertfordshire and Leicestershire, UK (Boatman & Stoate 2002), found that bird species tended to use a variety of cover crops, but whereas yellowhammers Emberiza citrinella used mainly cereals, greenfinches Carduelis chloris tended to use borage, sunflowers and mustard. Crops used by several species included kale, quinoa, fathen and linseed. Buckwheat was used a small amount, and apart from greenfinch, few others used sunflower or borage. Crops were sown in a randomised block design with three replicates at each of the three farms. Plots sizes were 20 or 50 m x 12 or 16 m. Numbers of birds feeding in, or flushed from each plot were recorded before 11:00 at weekly intervals from October-March 1998-2000.
A study of different set-aside crops at Allerton Research and Educational Trust Loddington farm, Leicestershire, UK (Murray et al. 2002), found that Eurasian skylark and yellowhammer used wild bird cover set-aside (kale set-aside, cereal set-aside, annual/biennial crop strips) more than expected compared to availability. Skylarks also used wild bird cover more than unmanaged set-aside, broad-leaved crops and other habitats. Yellowhammer used wild bird cover strips more than expected. Cereal set-aside wild bird cover was used significantly more than beetle banks, kale set-aside wild bird cover, unmanaged set-aside and ‘other’ habitats. Wild bird cover strips were used significantly more than kale set-aside, unmanaged set-aside and other habitats. Field margin and midfield set-aside strips 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. 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.
A small replicated controlled study from May-June in 1992-98 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 20 m wide mid-field and field-edge strips were planted with game cover crops (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 and yellowhammer). Nationally stable species rose (insignificantly) by 47% (eight species increased, four decreased). The other interventions employed were: ‘Manage hedges to benefit wildlife’, ‘Create beetle banks’, ‘Provide supplementary food’, ‘Control predators’ and ‘Reduce pesticide or herbicide use generally’.
A replicated, randomised, controlled study over the winters of 1998-2001 in 192 sites on 161 arable farms across England (Boatman et al. 2003) found that, of all the wild bird cover crops trialled, kale (Brassica spp.) was used by the widest range of species. Overall, all species analysed exhibited higher densities on wild bird cover crops over conventional crops except Eurasian skylarks, which preferred cereal stubbles. Although all species showed non-random and different wild bird cover crop preferences, kale was preferred by the greatest number of species. Additionally, bird abundance was significantly greater on wild bird cover crops located adjacent to hedgerows than those located midfield. Ten annual crops and four biennial crops were planted each year at each site with three replicates/crop. At 11 and 13 sites for 1999-2000 and 2000-2001 respectively strips containing the same crop were grown in pairs, one against a hedgerow and one infield, to determine location preference.
A replicated 2003 site comparison study of 88 farms in East Anglia and the West Midlands (Browne & Aebischer 2003) found that between 1998 and 2002 there was no difference in the decrease in autumn densities of grey partridge on farms that planted wild bird cover mixtures and farms that did not. Surveys for grey partridge were made once each autumn in 1998 and 2002 on 88 farms: 38 farms that planted wild bird cover and 50 farms that did not.
A replicated, controlled study over the winters of 1997-1998, 1998-1999 and 2000/01 in approximately 15 experimental and 15 control fields on one arable, autumn-sown crop farm in County Durham, England (Stoate et al. 2003) found that farmland bird abundance was significantly higher in wild bird cover crops than commercial crops (420 birds/km2 in wild bird cover vs. 30-40/km2 for commercial crops). Of 11 species with sufficient data for analysis, exhibited significant preference for wild bird cover crops in all species-year combinations birds. Of the wild bird cover crops, kale Brassica napus crops were preferred by nine species and quinoa Chenopodium quinoa crops by six species, although cereals and linseed were also used. The wild bird cover crops were planted in approximately 20 cm wide strips along one edge of arable wheat, barley or oil-seed rape fields. Bird counts were conducted twice monthly from October-March in 1997-1998; and three times per month from October-December as well as twice monthly from January-March in 1998-1999 and 2000-2001.
A replicated, randomised study between November 2003 and March 2004 in 205 cereal stubble fields under a range of management intensities in arable farmland in south Devon, UK (Defra 2004) found no clear changes in habitat use by seed-eating birds after the establishment of wild bird cover crops on some stubble fields. The target species, cirl bunting Emberiza cirlus, made insignificant use of wild bird cover crops (average of two individuals/plot). Only two plots contained >5 individuals and use of the habitat dropped drastically in March, which the authors suggest makes the habitat a poor alternative to stubbles. High numbers of other seed-eating species were recorded on the wild bird cover crops, especially those containing a mixture of rape, millet, linseed, kale and quinoa (maximum seed-eating bird count = 491 vs. 191 on barley fields). Only song thrush Turdus philomelos abundance was significantly positively related to wild bird cover presence. However, few stubble fields contained wild bird cover crops (13 fields with 24 wild bird cover strips) and the results may have been confounded by low sample size.
A replicated, controlled, before-and-after study from 1998-2003 (three years habitat manipulation and three years monitoring) in four cereal farms (12-20 km2) in the Beauce, Grande Beauce and Champagne Berrichonne regions, France (Bro et al. 2004) found that grey partridge populations were unaffected by cover strips. Neither breeding density nor the reproductive success of breeding pairs increased in managed compared to control areas. The survival rate was significantly lower in managed areas for all winters except for one winter in one site. Observations suggested that cover strips attracted predators, such as foxes Vulpes vulpes and hen harriers Circus cyaneus, causing the managed land to become ‘ecological traps’. Cover strips (500-1,000 ha/farm) were either set-asides or, typically, a maize-sorghum mixture.
A review of experiments on the effects of agri-environment measures on livestock farms in the UK (Buckingham et al. 2004) found that in one experiment in southwest England (the PEBIL project, also reported in (Defra 2003), birds preferred grass margins sown with plants providing seed food and cover over plots of grassland subject to various managements. The review assessed results from seven experiments (some incomplete at the time of the review) in Europe.
A replicated, randomised, controlled study over the winters of 1998-2001 in 192 plots of arable fields in lowland England (Henderson et al. 2004) found that farmland birds were significantly greater in density and diversity on wild bird cover crops than on conventional crops. Although there were no significant differences between wild bird covers containing a single plant species and conventional crops, bird density was 50 times higher on ‘preferred’ wild bird covers. Kale Brassica oleracae viridus-dominated wild bird cover supported the widest range of species (especially insectivores and seed-eaters), quinoa Chenopodium quinoa dominated wild bird cover were mainly used by finches and tree sparrows Passer montanus and (unharvested) seeding cereals were mainly used by buntings. Sunflowers, phacelia and buckwheat were the least preferred wild bird cover. All bird species, besides Eurasian skylarks, corn buntings Miliaria calandra and rooks Corvus frugilegus, were significantly denser on wild bird cover. The differences between wild bird cover were more marked in late-winter as kale and quinoa retained seeds for longer periods. Within each plot, one wild bird cover and up to four conventional crops were surveyed at least once.
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 farmland bird abundance and diversity were significantly higher in fields containing wild bird cover crops (0.6-4.2 ha sampled annually) than fields with set-aside, fields with overwinter stubble or fields with conventional crops. Bird density was up to 100 times higher/ha in wild bird cover crops than on control fields. The wild bird cover crops attracted 50% more species than set-aside and stubble fields; and 91% more than the conventional fields. Of eight species with sufficient data for individual analysis, seven were consistently significantly more abundant in wild bird cover than in control crops. However, skylarks were significantly more abundant in set-aside and stubble fields. The authors point out that many of the species that favour wild bird cover crops are those currently causing concern because of their declining populations.
A replicated, randomised, controlled study from June-September in 2001-02 of 21 cereal farms in eastern Scotland (Parish & Sotherton 2004) found that farmland birds were significantly more abundant on fields containing wild bird cover crops than on fields with conventional crops. A total of 25 species were recorded, with up to 80 times more birds seen in wild bird cover than in conventional crops. Over all month-crop combinations bird density was significantly higher on wild bird cover crops for all groups except finches in July. Bird density increased steadily over all months of the study on wild bird cover crops but remained relatively constant on conventional crops. Wild bird cover crops contained up to 90% more weed species and 280% more important bird-food weeds, than conventional crops. The wild bird cover crops were composed mainly of kale Brassica spp., quinoa Chenopodium quinoa and triticale Triticosecale spp. and were sown in strips (20 ? 650 m). A random sample of 4.9 ha of conventional crops was made on each farm.
A review of the results of four projects conducted from 1998-2004 of wild bird cover crops planted in arable farms in England (Stoate et al. 2004) found that the density and diversity of bird species increased significantly when wild bird cover crops were included in the farm. Four studies reported greater use of wild bird cover crops than of commercial crops during winter (October-March). One study reported an increase in bird abundance when wild bird cover crops were introduced into areas that previously lacked them. Kale Brassica napus and quinoa Chenopodium quinoa were used by the most species. Buckwheat was rarely used by species in any of the studies. Millet was used by more species than any other cereal. Three other studies also found that the location of wild bird covers within the whole-farm configuration had an effect on bird densities. Wild bird covers located close to hedges were favoured. Four studies found that a mixture of wild bird cover crops will produce the highest bird density and diversity.
A replicated, controlled, paired site study over winter (1997-1998) and summer (1999-2000) in arable farmlands in southern England and the Scottish lowlands (Sage et al. 2005) found that songbird density and species richness was higher in wild bird cover crops in both seasons. In total, more species were recorded in wild bird cover winter crops than control plots (26 vs. 10 species). Similarly, summer wild bird cover crops contained more species (14 vs. 10 species). Songbird abundance was significantly higher on wild bird cover winter (10-50 individuals/ha vs. 1) and summer (3 individuals/ha vs. 0.4) crops. There was significantly higher abundance of declining songbird species in the kale Brassica oleracea and quinoa Chenopodium quinoa but not cereal wild bird cover crops. Winter wild bird cover plots were sown with kale, quinoa or cereal while summer wild bird cover plots were predominantly triticale. Thirty experimental and 30 control plots were used in winter, with six experimental and six control plots in summer.
A replicated, controlled study in February-March 2002-03 on three arable farms in Mississippi, USA (Smith et al. 2005), found that densities of song sparrow Melospiza melodia were significantly higher in field margins seeded with Kobe lespedeza Lespedeza striata and partridge pea Chamaecrista fasciculata, compared to control field margins, when fields bordered blocks (> 30 m) of herbaceous vegetation (31 birds/ha vs. 8 birds/ha) or strips (<30 m) of woodland (38 birds/ha vs. 10 birds/ha), but not when fields bordered herbaceous strips (96 birds/ha vs. 70 birds/ha) or blocks of woodland (25 birds/ha vs. 28 birds/ha). Savannah sparrows Passerculus sandwichensis did not show any such variation, whilst other sparrow species (notably swamp sparrow M. georgiana) were significantly higher in uncultivated margins adjacent to herbaceous blocks (78 birds/ha vs. 19 birds/ha), herbaceous strips (139 birds/ha vs. 30 birds/ha) and wooded blocks (51 birds/ha vs. 12.6 birds/ha). Borders were established in 2000 and were seeded in 2000 and early 2001.
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 wildlife seed mixtures, overwinter stubble (see ‘Leave overwinter stubbles’) or set-aside (see ‘Provide or retain set-aside areas in farmland’). These were Eurasian skylarks (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.
A randomised, replicated, controlled trial on four farms in southwest England in 2003-2006 (Defra 2007) found that 12, 50 ´ 10 m plots of permanent pasture sown with a wild bird seed attracted more foraging songbirds (dunnock Prunella modularis, winter wren Troglodytes troglodytes, European robin Erithacus rubecula, seed-eating finches and buntings) than 12 control plots managed as silage (cut twice in May and July, and grazed in autumn/winter). Dunnocks, but not chaffinches Fringella coelebs or blackbirds Turdus merula, nested in hedgerows next to the sown plots more than expected, with 2.5 nests/km, compared to less than 0.5 nests/km in hedges next to experimental grass plots. Experimental plots were sown with a mix of crops including linseed and legumes. There were twelve replicates of each management type, monitored over the four years (2003-2006).
A randomised, replicated, controlled trial on four farms in southwest England (Pilgrim et al. 2007) (same study as Defra 2007) found that 50 ´ 10 m plots of permanent pasture sown with a mix of crops including linseed and legumes attracted more birds, and more bird species than control treatments, in both summer and winter. Plots were established in 2002, re-sown in new plots each year and monitored annually from 2003 to 2006. Legumes sown included white clover, red clover, common vetch and bird’s-foot trefoil. There were twelve replicates of each treatment.
A replicated controlled trial on one farm in Warwickshire, UK in 2005-2006 (Pywell & Nowakowski 2007) found that field corners or margins sown with a wild bird seed mix had more birds and bird species in winter than all other treatments. Fifty-five birds/plot from four species on average were recorded on the wild bird seed plots, compared to 0.1-1 bird/plot, or 0.1-0.7 species on average on control crop plots, plots sown with wildflower seed mix or left to naturally regenerate. The wild bird seed mix (five species) was sown in April 2006 and fertilised in late May 2006. The crop, oats, was sown in October 2005. Each treatment was tested in one section of margin and one corner in each of four fields. Farmland birds were counted on each plot on seven counts between December 2006 and March 2007.
A 2007 systematic review identified five papers investigating the effect of winter bird cover on farmland bird densities in the UK (Roberts & Pullins 2007). There were significantly higher densities of farmland birds in winter on fields with winter bird cover than on adjacent conventionally managed fields. The meta-analysis included experiments conducted between 1998 and 2001 from two controlled trials and one randomised control trial.
A replicated, randomised, controlled study in September, November, December and February in 2004-2005 in seven grassland farms (87-96% grass) in western Scotland (Parish & Sotherton 2008) found that songbirds responded significantly more positively to wild bird cover crops in grassland compared to arable regions. Average songbird densities were two orders of magnitude greater in wild bird cover crops than conventional crops (average 51 birds/ha vs. 0.2). The average density of songbirds in wild bird cover in the grassland region was more than double that in wild bird cover in the arable region at the same time of year (average 61.3 and 29.0 birds / ha respectively). Average densities in grassland conventional crops were just 14% of that in the arable region. On each site, an average of 1.2 ha of wild bird cover and 10.3 ha of conventional crops was randomly sampled. Arable farm data from a previous study was used for comparison.
A replicated experiment in northeast Scotland over three winters (2002-2005) (Perkins et al. 2008), found that unharvested seed-bearing crops were most frequently selected by birds (28% of all birds despite these patches occupying less than 5% of the area surveyed). For nine species, seed-bearing crops were used more than expected (based on available crop area) in at least one winter. Outside agri-environment schemes (the Rural Stewardship Scheme and Farmland Bird Lifeline), cereal stubble was the most selected habitat. In total, 53 lowland farms (23 in Rural Stewardship Scheme, 14 in Farmland Bird Lifeline, and 16 not in a scheme were assessed. Over 36,000 birds of 10 species were recorded.
The second monitoring year of the same study as (Pywell & Nowakowski 2007) in 2005-2007 Pywell and Nowakowski (2008) found that wild bird cover plots had more birds of more species in winter (86 birds/plot, of six species on average) than control cereal plots, plots sown with wildflower seed mix or left to naturally regenerate (2 birds/plot or less, and 0.4-1.6 species/plot on average). Farmland birds were counted on each plot on four counts between December 2007 and March 2008. The crop control in year two was winter wheat.
A 2009 literature review of agri-environment schemes in England (Natural England 2009) found that high densities of seed-eating songbirds and Eurasian skylarks were found on land planted with wild bird seed or cover mix and on stubble fields (see ‘Leave overwinter stubbles’). A survey in 2007-2008 found that densities of seed-eating songbirds were highest on wild bird seed or cover mix, compared to other agri-environment schemes options. 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 margins sown with wild bird cover crops such as quinoa Chenopodium quinoa and kale provided more food for seed-eating birds in late winter than other field margin types and supported large numbers of some songbird species.
A controlled study in 2002-2009 on mixed farmland in Hertfordshire, England (Aebischer & Ewald 2010), found that the estimated population density of grey partridges was significantly higher on land sown with wild bird cover than on conventional arable crops. This study also examined the densities found on land under various agri-environment schemes and set-aside (which were higher than those on wild bird cover, see ‘Pay farmers to cover the costs of conservation measures’ and ‘Provide or retain set-aside’) and the impact of predator control and supplementary food provision (see see ‘Provide supplementary food to increase adult survival’ and ‘Control predators not on islands’).
A follow-up review of experiments on the effects of agri-environment measures on livestock farms in the UK (Buckingham et al. 2010), found that in one experiment in southwest England (the PEBIL project, also reported (Defra 2007), small insect-eating birds preferred grassland margins sown with plants providing seed food over plots of grassland subject to various managements, despite there being no difference in insect numbers between the two sets of treatments. The preference for wild bird cover was attributed to easier accessibility (less dense ground cover). The review assessed results from four experimental projects (one incomplete at the time of the review) in the UK.
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 two agri-environment schemes, Countryside Stewardship Scheme and Environmental Stewardship, there was no consistent association between the provision of wild bird cover and farmland bird numbers. European greenfinch, stock dove Columba oenas, starling Sturnus vulgaris and woodpigeon Columba palumbus showed more positive population change (population increases or smaller decreases relative to other plots) in the 9 km² and 25 km² areas immediately surrounding plots planted with wild bird cover mix than in the area surrounding plots not planted with wildlife seed mixture. Although Eurasian linnet and rook also showed positive associations with wild bird cover mix at the 25 km² scale, plots with wild bird cover were associated with a greater decline in grey partridge populations at both scales between 2005 and 2008. 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 CSS. 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 of 2,046, 1 km squares of agricultural land across England in 2005 and 2008 (Davey et al. 2010) found that four of eight regions of England had at least two farmland birds that showed positive responses to wild bird cover and overwinter stubble fields (see ‘Leave overwinter stubbles’). Across all 15 species thought to benefit from these interventions, only one region (the North West) showed significantly more positive responses than would be expected by chance. Some species responded positively in some regions and negatively in others.
A replicated site comparison study on 1,031 agricultural sites across England in 2004-2008 (Ewald et al. 2010) found that the proportion of young grey partridges in the population was higher in 2007 and 2008 on sites with higher proportions of wild bird cover. Brood sizes were also related to wild bird cover in 2008 only. Overwinter survival was positively related to wild bird cover in 2004-2005 but negatively in 2007-2008. There were no relationships between wild bird cover and year-on-year density trends. This study describes the effects of several other interventions, discussed in the relevant sections.
A replicated 2010 site comparison study of 52 fields in East Anglia and the West Midlands, UK, (Field et al. 2010) found no difference between the number of seed-eating birds in fields managed under the Higher Level Strata of the Environmental Stewardship scheme (i.e. on fields planted with Enhanced Wild Bird Seed Mix) than in fields managed under the Entry Level Strata of the Environmental Stewardship scheme (i.e. fields planted with wild bird cover mix). In East Anglia, but not the West Midlands, there were significantly more seed-eating birds on fields planted with wild bird cover under the Environmental Stewardship scheme (59 birds/ha) than non-Environmental Stewardship fields planted with a game cover (2 birds/ha). Seed-eating birds were surveyed on two visits to each site between 1 November 2007 and 29 February 2008.
A replicated site comparison study on farms in two English regions (Field et al. 2010) found that more seed-eating farmland songbirds (including tree sparrow and corn bunting) were found on Higher Level Stewardship wild bird seed mix sites than on non-stewardship game cover crops in East Anglia (6-11 birds/ha on wild bird seed mix, compared to <0.5 birds/ha on game cover), but not in the West Midlands (2-4 birds/ha on both types). 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.
A replicated study from April-July in 2006 on four livestock farms (3 replicates/farm) in southwest England (Holt et al. 2010) found that dunnock Prunella modularis, but not Eurasian blackbird Turdus merula or chaffinch, nested at higher densities in hedges alongside field margins sown with wild bird seed crops, or barley undersown with grass and clover, compared to those next to grassy field edges under various management options (dunnocks: approximately 2.5 nests/km for seed crops vs. 0.3/km for grass margins; blackbirds: 1.0 vs. 1.3; chaffinch: 1.5 vs. 1.4). Margins were 10 m wide, 50 m long and located adjacent to existing hedgerows. Seed crop margins were sown with barley (undersown with grass/legumes) or a kale/quinoa mix. There were 12 replicates of each treatment. This study reports on results from the same experiment as Defra 2007.
A replicated study on four farms in Gloucestershire and Oxfordshire, England, in 2007 (Rantanen et al. 2010) found that grey partridge released in coveys in the autumn used cover crops more frequently than birds released in pairs in the spring. This study is discussed in ‘Captive breeding, rearing and releases (ex situ conservation)’.
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