Action: Plant wild bird seed or cover mixture
- Thirty individual studies investigated the effects on birds of sowing wild bird seed or cover mixture, 21 studies found positive effects. Fourteen studies from the UK (including one systematic review and nine replicated controlled trials of which four randomized, and three reviews) found that fields sown with wild bird cover mix had higher abundance, density, species diversity and species richness of birds than other farmland habitats. Six studies from the UK (including one review and two replicated studies) found that birds showed a preference for wild bird cover and used it significantly more than other habitats. One review found the grey partridge population increased substantially on farms where conservation measures including cover crops were in place. Nine replicated studies from France and the UK reported mixed or negative effects of wild bird cover on birds compared to other farmland habitats. Six studies found that mixtures including kale or a mixture of kale and/or other species attracted the largest number of bird species or highest bird abundance.
- Twelve studies from the UK looked at the effects of wild bird cover strips on invertebrates. Seven studies from the UK (including one review and four replicated controlled studies of which two were also randomized) found positive effects. Farmland habitats sown with wild bird cover mix were used more by butterflies, and had a higher abundance or species richness of butterflies and/or bees than other farmland habitats. One review found wild bird cover benefited invertebrates. Four studies (including one review and two replicated trials) reported mixed or negative effects of wild bird cover on invertebrate numbers compared with other farmland habitats. One study found that bees and butterflies showed preferences for particular plant species.
- Eight studies from the UK looked at plants and wild bird cover. Six studies (including two reviews and two replicated controlled trials) found that planting wild bird cover mix was one of the three best options for conservation of annual herbaceous plant communities, benefited plants and resulted in increased plant diversity and species richness. However two replicated studies (of which one a site comparison) found mixed/negative effects for plant species richness.
- One replicated trial from the UK found that small mammal activity was higher in wild bird cover than in the crop in winter but not in summer.
The loss of food supplies, especially seeds, is thought to be a key driver of farmland bird declines. Plants that provide seed food and cover for wild birds include maize, sunflower and cereals. Wild bird cover crops are often planted in blocks or 6 m-wide strips and left unharvested. These are sometimes called ‘game crops’ or ‘game cover crops’. They may also provide benefits for other farmland wildlife.
Supporting evidence from individual studies
A study of habitat use by yellowhammers Emberiza citrinella in 1993, 1995 and 1997 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, and 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 Brassica spp. 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 trips per nest were plotted in 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 trial from 1995 to 1998 in Hampshire, UK (Carreck et al. 1999) recorded fewer flowering plant species, bee (Apidae), fly (Diptera) and butterfly (Lepidoptera) species on a single field margin strip sown with wild bird cover seed mix established for three years compared to three strips sown with a diverse wildflower seed mix. There were 20 flowering plant species, eight bee (Apidae), three fly (Diptera) and three butterfly (Lepidoptera) species on the single field margin strip sown with wild bird cover seed mix established for three years in 1998, and 24, nine, seven and eight plant, bee, butterfly and fly species respectively on three wildflower seed mix strips in the same study. The wild bird mix strip had more plant species but fewer bee, fly and butterfly species than a single naturally regenerated field margin strip (16, nine, four and six plant, bee, butterfly and fly species respectively on the naturally regenerated strip). The field margins were established or sown in 1995. Numbers of inflorescences or flowers and flower-visiting bees, wasps (Hymenoptera), flies and butterflies were counted on a 200 x 2 m transect in each strip, once a month from May to August 1998.
A 2000 literature review from the UK (Aebischer et al. 2000) found that populations of grey partridge Perdix perdix were 600% higher on farms where conservation measures aimed at partridges were in place, compared to farms without these measures (Aebischer 1997). Measures included the provision of conservation headlands, planting cover crops, using set-aside and creating beetle banks.
Aebischer N.J. (1997) Gamebirds: management of the Grey Partridge in Britain. Pages 131-151 in: M. Bolton (ed.) Conservation and the Use of Wildlife Resources. Chapman & Hall, London.
A small study of set-aside strips from 1995 to 1999 at Loddington, Leicestershire, UK (Boatman & Bence 2000) found that set-aside sown with wild bird cover was used by nesting Eurasian skylark Alauda arvensis and butterflies (Lepidoptera) significantly more than other habitats. The majority of skylark territories found were within set-aside strips (margins or midfield) sown with wild bird cover (1995: 76%, 1996: 65%, 1997: 71%, 1999: 55%), although the habitat covered only 8-10% of the area. The habitat was also used more for foraging than all habitats, except linseed Linum usitatissimum. Transects along wild bird cover set-aside strips also had more butterfly records than any other habitat in 1997 and 1998 (28-40% vs 1-18%). Wild bird cover was sown with either cereal-based or kale-based Brassica spp. mixtures. Skylark territories were recorded in 1995-1997 and 1999 and nests were located in 1999 and foraging trips observed for two 1.5 hour periods. Two butterfly transects were walked weekly from April-September.
A replicated, randomized study from 1998 to 2000 of annual and biennial crops in Norfolk, Hertfordshire and Leicestershire, UK (Boatman & Stoate 2002) found that bird species tended to use a variety of crops. Yellowhammers Emberiza citrinella used mainly cereals. Greenfinch Carduelis chloris tended to use borage Borago officinalis, sunflowers Helianthus spp. and mustard Brassica juncea. Crops used by several bird species included kale Brassica oleracea, quinoa Chenopodium quinoa, fat hen Chenopodium album and linseed Linum usitatissimum. Buckwheat Fagopyron esculentum was used a small amount and, apart from greenfinch, few others used sunflower or borage. Crops were sown in a randomized block design with three replicates at each of the three farms. Plots were 20 or 50 m x either 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 review (Evans et al. 2002) of two reports (Wilson 2000, ADAS 2001) evaluating the effects of the Pilot Arable Stewardship Scheme in two regions in the UK (East Anglia and the West Midlands) from 1998 to 2003 found that ‘wildlife seed mix’ benefited plants, bumblebees Bombus spp., bugs (Hemiptera) and sawflies (Symphyta), but not ground beetles (Carabidae). The wildlife seed mix option could be wild bird seed mix or nectar and pollen mix for pollinators, and the review does not distinguish between these mixes. The effects of the pilot scheme on plants, invertebrates and birds were monitored over three years, relative to control areas, or control farms. Only plants and invertebrates were measured within individual options. Wildlife seed mix was the least widely implemented option, with total areas of 106 and 152 ha in East Anglia and the West Midlands respectively.
Wilson S., Baylis M., Sherrott A. & Howe, G. (2000) Arable Stewardship Project Officer Review. F. a. R. C. Agency report.
ADAS (2001) Ecological evaluation of the Arable Stewardship Pilot Scheme, 1998-2000. ADAS report.
A replicated study in June 2000 in ten edge habitats on an arable farm in Leicestershire, England (Moreby 2002) found that first-year wild bird cover had the highest density (not significant) of caterpillars (Lepidoptera). Weevil (Curculionidae) densities were similar in first- and second-year wild bird cover but lower than in edges of non-rotational set-aside. Spider (Araneae) and rove beetle (Staphylinidae) densities were lower in wild bird cover than in ungrazed pasture edges. Type of neighbouring crop did not affect invertebrate densities in the different habitats. Apart from the four habitats mentioned above, beetle banks, brood cover, hedge bottoms, sheep-grazed pasture edges, grass/wire fence lines and winter wheat headlands were included in the study. Invertebrates were sampled with a vacuum suction sampler in June 2000. This study was part of the same experimental set-up as Moreby & Southway (2002), Murray et al. (2002).
A replicated study from 1995 to 1999 of arable habitats on a farm in Leicestershire, UK (Moreby & Southway 2002) found that the abundance of some invertebrate groups was higher in non-crop strips (wild bird cover or grass beetle banks), whereas other groups were more abundant in crops. Four invertebrate groups tended to have significantly higher densities in non-crop strips than crops in all years spiders (Araneae) 7 vs 1-5 individuals/sample, true bugs (Homoptera) 29 vs 1-4, typical bugs (Heteroptera) 10-58 vs 0-9, and key ‘chick food insects’ 65 vs 2-10. In three of the years, true weevils (Curculionidae) were found at significantly higher densities in non-crop strips and beans (0-11) than other crops (0-2). In contrast, in three or four of the years, densities in crops were significantly higher than non-crops for: true flies (Diptera) 20-230 vs 25-100 individuals and aphids (Aphididae). Moth and butterfly larvae (Lepidoptera) and ground beetles (Carabidae) differed significantly in only one or two years, when density was higher in crops than non-crops. Total beetles (Coleoptera) varied between years and habitats. Sawfly larvae (Symphyta), leaf beetles (Chrysomelidae) and soldier beetles (Cantharidae) showed no significant differences. Wild bird cover was sown as 2-5 m-wide strips along field boundaries and re-sown every few years with a cereal or kale-based Brassica spp. mixture. Grass strips (1 m-wide) were sown onto a raised bank along edges or across the centre of fields. Invertebrates were sampled each year in the centre of 5-11 grass/wild bird cover strips and 3 m into 3-4 pasture, 8-12 wheat, 6-8 barley, 3-6 oilseed rape and four field bean fields. Two samples of 0.5 m² were taken in each habitat using a D-Vac suction sampler in June 1995-1999. This study was part of the same experimental set-up as Moreby (2002), Murray et al. (2002).
A study of different set-aside crops on a farm in Leicestershire, UK (Murray et al. 2002), found that Eurasian skylark Alauda arvensis and yellowhammer Emberiza citrinella used wild bird cover set-aside (kale Brassica napus 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. This study was part of the same experimental set-up as Moreby (2002), Moreby & Southway (2002).
A small replicated controlled study from May-June 1992-1998 in Leicestershire, UK (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). However, 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 Alauda arvensis and yellowhammer Emberiza citrinella). Nationally stable species rose (insignificantly) by 47% (eight species increased, four decreased). The other interventions employed at the same site were managing hedges, beetle banks, supplementary feeding, predator control and reducing chemical inputs generally.
A replicated, randomized, controlled study over the winters of 1998-2001 on 161 arable farms across England (Boatman et al. 2003) (same study as (Henderson et al. 2004)) found that, overall, all bird species analysed exhibited higher densities on wild bird cover crops than on conventional crops except Eurasian skylark Alauda arvensis, which preferred cereal stubbles. Although all species showed non-random and different wild bird cover crop preferences, kale Brassica spp. 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 of 192 sites with 3 replicates/crop. At 11 and 13 sites in 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 site comparison study of 88 farms in East Anglia and the West Midlands, UK (Browne & Aebischer 2003) found that between 1998 and 2002 there was no difference in the decrease in autumn densities of grey partridge Perdix perdix 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 2000-2001 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, all species-year combinations exhibited significant preferences for wild bird cover crops. Of the wild bird cover crops, kale Brassica napus crops were preferred by nine species and quinoa Chenopodium quinoa crops by six species; cereals and linseed Linum usitatissimum were also used. The wild bird cover crops were planted in c. 20 m-wide strips along one edge of arable wheat, barley or oilseed rape fields. There were approximately 15 experimental and 15 control 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, controlled, before-and-after study from 1998 to 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 Perdix perdix 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. Partridges were surveyed in March and mid-December to early-January to assess overwinter mortality, and in August to assess reproductive success.
A 2004 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 Potential to Enhance Biodiversity in Intensive Livestock farms (PEBIL) project, also reported in (Defra 2007)), birds preferred grass margins sown with plants providing seed food and cover, over plots of grassland subject to various management treatments. The review assessed results from seven experiments (some incomplete at the time of the review) in the UK and Europe.
A replicated study in the summers of 1999-2000 comparing ten different conservation measures on arable farms in the UK (Critchley et al. 2004) found that wildlife seed mixtures (site-specific mixture, but largely planted for birds) appeared to be one of the three best options for the conservation of annual herbaceous plant communities. Uncropped cultivated margins and no-fertilizer conservation headlands were the other two options. The average numbers of plant species in different conservation habitats were wildlife seed mixtures 6.7, uncropped cultivated margins 6.3, undersown cereals 5.9, naturally regenerated grass margins 5.5, no-fertilizer conservation headlands 4.8, spring fallows 4.5, sown grass margins 4.4, overwinter stubbles 4.2, conservation headlands 3.5, grass leys 3.1. Plant species richness was highest in wildlife seed mixtures due to the range of sown species and a high number of annual arable species. Plants were surveyed on a total of 294 conservation measure sites (each a single field, block of field or field margin strip), on 37 farms in East Anglia (dominated by arable farming) and 38 farms in the West Midlands (dominated by more mixed farming). The ten habitats were created according to agri-environment scheme guidelines. Vegetation was surveyed once in each site in June-August in 1999 or 2000 in thirty 0.25 m2 quadrats randomly placed in 50-100 m randomly located sampling zones in each habitat site. All vascular plant species rooted in each quadrat, bare ground, or litter and plant cover were recorded.
A replicated, randomized study from November 2003 to March 2004 in 205 cereal stubble fields 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 2 individuals/plot). Only two plots contained more than five 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 including chaffinch Fringilla coelebs and yellowhammer Emberiza citrinella were recorded on the wild bird cover crops, especially those containing a mixture of rape, millet, linseed Linum usitatissimum, kale Brassica spp. and quinoa Chenopodium quinoa (maximum seed-eating bird count 491 on wild bird cover 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, randomized, controlled study over the winters of 1998-2001 in 192 plots of arable fields in lowland England (Henderson et al. 2004) (same study as (Boatman et al. 2003)) found significantly higher density and diversity of farmland birds on wild bird cover crops than 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 covers supported the widest range of bird species (especially insectivores and seed-eaters), quinoa Chenopodium quinoa-dominated wild bird covers were mainly used by finches and tree sparrows Passer montanus and (unharvested) seeding cereals were mainly used by buntings. Sunflowers Helianthus spp., phacelia Phacelia spp. and buckwheat Fagopyron esculentum were the least preferred wild bird covers. All species, except Eurasian skylark Alauda arvensis, corn bunting Miliaria calandra and rook Corvus frugilegus, were significantly denser on wild bird cover. The differences between wild bird covers were more marked in late-winter as kale and quinoa Chenopodium 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, randomized, controlled study from November-February in 2000-2001 and 2001-2002 on 20 arable farms in eastern Scotland (Parish & Sotherton 2004a) 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. Wild bird cover crops attracted 50% more species than set-aside and stubble fields and 91% more than 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, Eurasian skylarks Alauda arvensis 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, randomized, controlled study from June-September 2001-2002 of 21 cereal farms in eastern Scotland (Parish & Sotherton 2004b) 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 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 20 x 650 m strips. 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 to 2004 on 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 Fagopyron esculentum 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 sites 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 were 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 than control plots (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 a 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 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 or set aside. These were Eurasian skylark Alauda arvensis (a field-nesting species) and Eurasian linnet 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 replicated site comparison study in 1999 and 2003 in the UK (Critchley et al. 2007) found that 33 field margins sown with a locally specific ‘wildlife seed mixture’ had greater numbers of perennial plants and pernicious weeds after four years, but the total number of plant species did not increase (7-8 plant species/margin). This option was not considered the best option for the conservation of arable plants. The most commonly sown plant species were brassicas (sown at 14 sites). Cereals, maize Zea mays, buckwheat Fagopyron esculentum, borage Borago officinalis, grasses, legumes, teasel Dipsacus fullonum and phacelia Phacelia tanacetifolia were also sown at some sites. Plants were surveyed in thirty 0.025 m2 quadrats within a 100 m sampling zone. Percentage cover and plant species were recorded.
A randomized, replicated, controlled trial from 2003 to 2006 in southwest England (Defra 2007) found that plots of permanent pasture sown with a wild bird seed mix attracted more foraging songbirds (dunnock Prunella modularis, wren Troglodytes troglodytes, European robin Erithacus rubecula, seed-eating finches (Fringillidae) and buntings (Emberizidae)) 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. Twelve experimental plots (50 x 10 m) were sown on four farms with a mix of crops including linseed Linum usitatissimum and legumes. There were twelve replicates of each management type, monitored over four years. This study was part of the same experimental set-up as (Pilgrim et al. 2007, Potts et al. 2009, Holt et al. 2010).
A 2007 review of published and unpublished literature (Fisher et al. 2007) found experimental evidence of benefits of wild bird seed or cover mix to plants (one study (Critchley et al. 2004)) and invertebrates (true bugs (Hemiptera) Gardner et al. 2001, and bumblebees Bombus spp. Allen et al. 2001).
Allen D.S., Gundrey A.L. & Gardner S.M. (2001) Bumblebees. Technical appendix to ecological evaluation of arable stewardship pilot scheme 1998-2000. ADAS, Wolverhampton, UK.
Gardner S.M., Allen D.S., Woodward J., Mole A.C. & Gundrey A.L. (2001) True bugs. Technical appendix to ecological evaluation of arable stewardship pilot scheme 1998-2000. ADAS, Wolverhampton, UK.
A randomized, replicated, controlled trial from 2003 to 2006 in southwest England (Pilgrim et al. 2007) found that plots of permanent pasture sown with a mix of crops including linseed Linum usitatissimum and legumes attracted more birds, and more bird species, than control treatments, in both summer and winter. Three plots (50 x 10 m) were established on each of four farms in 2002 re-sown in new plots each year and monitored annually from 2003 to 2006. Legumes sown included white clover Trifolium repens, red clover T. pratense, common vetch Vicia sativa and bird’s-foot trefoil Lotus corniculatus. There were twelve replicates of each treatment. This study was part of the same experimental set-up as (Defra 2007, Potts et al. 2009, Holt et al. 2010).
A replicated controlled trial in 2005-2006 in Warwickshire, UK (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, and more plant species, bumblebees Bombus spp. and butterflies (Lepidoptera) (individuals and species) than control plots sown with winter oats. Fifty-five birds/plot from four species on average were recorded on the wild bird seed plots compared to 0.1-1 bird/plot and 0.1-0.7 species on average on control crop plots, plots sown with wildflower seed mix and plots left to naturally regenerate. There were 11 plant species/m2 , 25 bumblebees and four bumblebee species/plot, 25 butterflies and six butterfly species/plot on wild bird seed plots, compared to two plant species/m2, no bumblebees, one butterfly and 0.9 butterfly species/plot in control cereal crop plots. Each treatment was tested in one section of margin and one corner in each of four fields. The wild bird seed mix (five species) was sown in April 2006 and fertilized in late May 2006. The crop (oats) was sown in October 2005. Plants were monitored in three 1 m2 quadrats/plot in July 2006. Butterflies, bumblebees and flowering plants were recorded on a 6 m-wide transect five times between July and September 2006. Farmland birds were counted on each plot on seven counts between December 2006 and March 2007. The second monitoring year of the same study is presented in (Pywell & Nowakowski 2008).
A replicated trial in 2004 and 2005 on four farms in England (Pywell et al. 2007) found that plants, insects, mammals and birds all used sown wild bird seed mix plots more than wheat crop at some times of year. The number of flowers and flowering species, the abundance and number of species of butterflies (Lepidoptera) and the number of bumblebee species Bombus spp., were all higher in the wild bird mix than in the crop. Small mammal activity was higher in the wild bird mix in winter (around 25 mammals/100 trap nights in wild bird mix, compared to around 8 in the crop), and higher in the crop in summer (around 10 mammals caught in the crop, compared to less than one on average in the wild bird mix). The number of birds and bird species were higher in the wild bird mix than the crop in December and January (around 100 birds of over three species per count on average in the wild bird mix, compared to less than 10 birds or <1 species in the crop), but not in February and March. Eurasian linnet Acanthis cannabina (at three sites) and reed bunting Emberiza schoeniclus (at one site) were the most abundant bird species recorded in the wild bird mix. A seed mix containing white millet Echinochloa esculenta, linseed Linum usitatissimum, radish Raphanus sativus and quinoa Chenopodium quinoa was sown in a 150 x 30 m patch in the centre of an arable field (winter wheat) on each of four farms in Cambridgeshire, Bedfordshire, Oxfordshire and Buckinghamshire, in April 2004 and 2005. Plants, bees and butterflies were counted in summer 2005. Small mammals were trapped in November-December 2005 and May-June 2005. Birds were counted once a month between December 2004 and March 2005.
A 2007 systematic review identified five papers investigating the effect of winter bird cover on farmland bird densities in the UK (Roberts & Pullin 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 randomized control trial.
A replicated, controlled, randomized study on 28 arable farms in East Anglia and southern England (Anon 2008) found that as the area sown with cover crops increased plant diversity in both regions, numbers of butterflies (Lepidoptera) in East Anglia and bees (Apidae) in southern England increased. Results also suggested that cover crops sown in strips have greater butterfly diversity than those sown in blocks, this did not appear to be the case for bees, but numbers recorded were low in the wet cool summer. One of six treatments was randomly allocated to each farm (two replicates per region): 1.5 ha or 6 ha of project-managed uncropped land in either strips or blocks, or 1.5 ha or 6 ha of farm-managed uncropped land. Two organic farms were also selected per region. Uncropped land was split into four equal areas comprising a floristically-enhanced grass mix, a plant mix to provide summer cover and foraging (e.g. mustard, legume, cereal mixture), a mix to provide winter cover and foraging (e.g. cereal/kale Brassica spp./quinoa Chenopodium quinoa mixture) and annual cultivation to encourage annual arable plants. Plants (April and June) and insects were assessed within and at the edge of three fields (cereal crop, non-cereal crop and uncropped field in 2006-2009). Butterfly, bee and hoverfly (Syrphidae) diversity and abundance were recorded during transect walks in July.
A replicated, randomized, 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 and 29 birds/ha respectively). Average bird 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.
A randomized, replicated study in 2006 and 2007 in Warwickshire, UK (Pywell et al. 2008) (same study as (Pywell et al. 2010)) found that butterflies (Lepidoptera) and bumblebees Bombus spp. displayed different preferences for 13 annual and perennial plant species, 10 of which were typical components of wild bird seed mixtures. In 2006, more butterflies were found in plots sown with lucerne Medicago sativa (6.3 butterflies/plot) than plots sown with borage Borago officinalis (0.3), chicory Cichorium intybus (0.8) and sainfoin Onobrychis viciifolia (0.8). More butterfly species were found in lucerne plots (3.5 species/plot) than in borage, chicory, sainfoin and fodder radish Raphanus sativus (0.3-0.5). In 2007, red clover Trifolium pratense plots had the largest number of butterflies, significantly more than chicory (3.3 vs 0.0 butterflies/plot), whilst all other plant species ranged between 0.3-2.3. In both years, bumblebees were most abundant in phacelia Phacelia tanacetifolia plots (134 and 38.5 bumblebees/plot in 2006 and 2007), followed by borage (100 and 32). Crimson clover T. incarnatum and sunflower Helianthus annuus (37 and 26 respectively) had more bumblebees than other plant species (0-6) in 2006. Red clover plots had more bumblebees (21) than buckwheat Fagopyrum esculentum, chicory, linseed Linum usitatissimum, lucerne, mustard Brassica juncea or sweet clover Melilotus officinalis in 2007. The number of bumblebee species recorded in crimson clover, phacelia, borage and sunflower was significantly higher than all other plant species (2.8-4.0 vs 0-1.3 species/plot) in 2006. In 2007, red clover in addition to the four species from 2006 had significantly more bumblebee species than mustard (3.0-3.3 vs 0.5 species/plot). Short-tongued bees showed a significant preference for phacelia and borage compared with all other treatments in both years. Long-tongued bees showed a significant preference for crimson clover over all other species apart from borage and phacelia in 2006, and red clover in 2007 (although they also showed a strong preference for crimson clover and sainfoin in 2007). Peak flowering of many important bee forage species was in late July, including phacelia, borage, red clover and sweet clover. Thirteen species were sown in single species stands in 6 x 4 m plots with four replicates in May 2006. Annual species were re-established in the same plots in May 2007. Abundance and diversity of butterflies and bumblebees were recorded on transects in each plot six times between July and September 2006 and May and September 2007. On each visit the percentage cover of flowers of all dicot species/plot was estimated.
The second monitoring year of the same study as (Pywell & Nowakowski 2007) in the UK (Pywell & Nowakowski 2008) found that wild bird seed mix plots had more birds in winter (86 birds/plot, of six species on average) than control cereal plots, plots sown with wildflower seed mix or plots left to naturally regenerate (2 birds/plot or less, and 0.4-1.6 species/plot on average). Wild bird seed plots also had more bumblebee Bombus spp. and butterfly (Lepidoptera) individuals and species than naturally regenerated or control cereal plots and more vacuum-sampled invertebrates than control plots. Wild bird seed plots had eight plant species/m2, 40 bumblebees and four bumblebee species/plot, 18 butterflies and six butterfly species/plot, compared to three plant species/m2, no bumblebees and one butterfly/plot on control cereal plots. Control plots had 254 vacuum-sampled canopy-dwelling invertebrates/m2 on average, compared to 840-1,197/m2 on other treatments. Plants were monitored in three 1 m2 quadrats/plot in June 2007. Butterflies, bumblebees and flowering plants were recorded in a 6 m-wide transect six times between July and September 2006 and 2007. Invertebrates in the vegetation were vacuum sampled in early July 2007. 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 skylark Alauda arvensis were found on land planted with wild bird seed or cover mix and on stubble fields. 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 scheme options.
A randomized, replicated, controlled trial from 2003 to 2006 in southwest England (Potts et al. 2009) found plots on permanent pasture annually sown with a mix of legumes, or grass and legumes, supported more common bumblebees Bombus spp. (individuals and species) than seven grass management options. In the first two years, the numbers of common butterflies (Lepidoptera) and common butterfly species were higher in plots sown with legumes than in five intensively managed grassland treatments. No more than 2.2 bumblebees/transect were recorded on average on any grass-only plot in any year, compared to over 15 bumblebees/transect in both sown treatments in 2003. The plots sown with legumes generally had fewer butterfly larvae than all grass-only treatments, including conventional silage and six different management treatments. Experimental plots 50 x 10 m were established on permanent pastures (more than five-years-old) on four farms. There were nine different management types, with three replicates/farm, monitored over four years. Seven management types involved different management options for grass-only plots, including mowing and fertilizer addition. The two legume-sown treatments comprised either a mix of crops sown partly for wild birds, including linseed Linum usitatissimum and legumes, uncut, or spring barley Hordeum vulgare undersown with a grass and legume mix (white clover Trifolium repens, red clover T. pratense, common vetch Vicia sativa, bird’s?foot trefoil Lotus corniculatus and black medick Medicago lupulina) cut once in July. Bumblebees and butterflies were surveyed along a 50 m transect line in the centre of each experimental plot, once a month from June to September annually. Butterfly larvae were sampled on two 10 m transects using a sweep net in April and June-September annually. This study was part of the same experimental set-up as (Defra 2007, Pilgrim et al. 2007, Holt et al. 2010).
A 2009 literature review of European farmland conservation practices (Vickery et al. 2009) found that margins sown with wild bird cover had high numbers of some invertebrates which are important bird food, but lower numbers than on margins sown with a wildflower mix. Cover crops such as quinoa Chenopodium quinoa and kale Brassica oleracea 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 Perdix perdix 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) and the impact of predator control and supplementary food provision. Grey partridges were surveyed in March and September using dawn and dusk counts starting in 2001. Land cover within the project area was mapped and categorized as: conventional arable land, arable in agri-environment schemes, non-arable, or set-aside (which was further divided into non-rotational, wild bird cover, other rotational).
A 2010 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 Potential for Enhancing Biodiversity on Intensive Livestock Farms PEBIL project BD1444, also reported in (Defra 2007)) found small insect-eating birds preferred field margins sown with a diverse mixture of plants that provided seed food; compared to grass margins subject to different management techniques, despite there being no difference in the number of insects 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 site comparison in 2005 and 2008 of 2,046, 1 km squares of agricultural land across England (Davey et al. 2010a) (same study as (Davey et al. 2010b)) found that four of eight regions had at least two farmland birds that showed positive responses to wild bird cover and overwinter stubble fields. Across all 15 bird 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 in 2005 and 2008 of 2,046, 1 km² plots of lowland farmland in England (Davey et al. 2010b) (same study as (Davey et al. 2010a)) found that three years after the 2005 introduction of two agri-environment schemes, Countryside Stewardship Scheme and Entry Level Stewardship, there was no consistent association between the provision of wild bird cover and farmland bird numbers. European greenfinch Carduelis chloris, 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 Carduelis cannabina and rook Corvus frugilegus 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 Perdix perdix 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 Entry Level Stewardship or the Countryside Stewardship Scheme. 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 study from 2004 to 2008 in England (Ewald et al. 2010) found that the ratio of young-to-old grey partridges Perdix perdix 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. Spring and autumn counts of grey partridge were made at 1031 sites across England as part of the Partridge Count Scheme.
A replicated site comparison study between November 2007 and February 2008 of 52 fields in East Anglia and the West Midlands (Field et al. 2010a) (same study as (Field et al. 2010b)) found no difference between the number of seed-eating birds in fields managed under Higher Level Stewardship of the Environmental Stewardship scheme (fields sown with enhanced wild bird seed mix) than in fields managed under Entry Level Stewardship of the Environmental Stewardship scheme (fields sown 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 (59.3 birds/ha) than non-Environmental Stewardship fields planted with a game cover (2.1 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 in winter 2007-2008 on farms in East Anglia and the West Midlands, England (Field et al. 2010b) (same study as (Field et al. 2010a)) found that more seed-eating farmland songbirds (including tree sparrow Passer montanus and corn bunting Emberiza calandra) were found on Higher Level Stewardship wild bird seed mix sites (6-11 birds/ha) than on non-stewardship game cover crops (<0.5 birds/ha) in East Anglia, but not in the West Midlands (2-4 birds/ha on both types). The survey was carried out on 27 farms with Higher Level Stewardship, 13 farms with Entry Level Stewardship and 14 with no environmental stewardship.
A replicated study from April-July in 2006 on four livestock farms in southwest England (Holt et al. 2010) found that dunnock Prunella modularis, but not Eurasian blackbird Turdus merula or chaffinch Fringella coelebs, 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 (dunnock: 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 x 50 m and located adjacent to existing hedgerows. Seed crop margins were sown with barley (undersown with grass/legumes) or a kale Brassica spp./quinoa Chenopodium quinoa mix. There were 12 replicates of each treatment, three replicates on each farm. This study was part of the same experimental set-up as (Defra 2007, Pilgrim et al. 2007, Potts et al. 2009).
A replicated, randomized study in 2006 and 2007 in Warwickshire, UK (Pywell et al. 2010) (same study as (Pywell et al. 2008)) found bee (Apidae) and butterfly (Lepidoptera) abundance and species richness were higher in stands of specific sown plant species. Bumblebee Bombus spp. abundance and species richness were significantly higher on plots sown with phacelia Phacelia tanacetifolia and borage Borago officinalis (32-85 bees/plot) compared to other treatments (1-22 bees/plot). Crimson clover Trifolium incarnatum (10-21 bees/plot), sunflower Helianthus annuus (10-22) and in 2007 red clover Trifolium pratense (20) also tended to have high bee abundances (other plant species: 1-11 bees/plot). Short- and long-tongued bees showed differences in preferences. In 2006, butterfly abundance and species richness were significantly higher in plots with lucerne Medicago sativa compared to borage, chicory Cichorium intybus and sainfoin Onobrychis viciifolia. In 2007 butterfly abundance was higher in red clover compared with chicory, but the number of species did not differ between treatments. Mobile and immobile butterfly species showed differences in preferences. Flowers of buckwheat Fagopyrum esculentum were the most abundant followed by phacelia, borage and sunflower in 2006. In 2007 fodder radish, red clover and sweet clover Melilotus officinalis also had high flower abundance. Mustard Brassica juncea and linseed Linum usitatissimum had the least abundant flowers in both years, along with other species each year. Thirteen species were sown in single species stands: nine small-seeded crop species typically sown in wild bird seed mixes and four wildflower species typically sown in pollen and nectar seed mixes. The species were sown in May each year in adjacent 6 x 4 m plots in a randomized block experiment with four replicates. Butterflies and bumblebees were sampled by walking transects through each plot on six occasions from May-September. Flower cover was estimated at the same time.
A replicated study on four farms in Gloucestershire and Oxfordshire, England, in 2007 (Rantanen et al. 2010) found that grey partridge Perdix perdix released in coveys in the autumn used cover crops more frequently than birds released in pairs in the spring. Four farms were studied. Birds were radio-tagged and their positions marked on a 1:5000 map.
A replicated controlled study in summer 2008 in northwest Scotland (Redpath et al. 2010) found that croft sections (an agricultural system specific to Scotland, consisting of small agricultural units with rotational cropping regimes and livestock production) sown with a brassica-rich ‘bird and bumblebee’ conservation seed mix had 47 times more foraging bumblebees than sheep-grazed sections and 16 times more bumblebees Bombus spp. than winter-grazed pastures in June. In July the ‘bird and bumblebee’ mix sections had 248 and 65 times more bumblebees than sections grazed by sheep or both sheep and cattle respectively. The number of bumblebees in July was also significantly higher (4-16 times) in ‘bird and bumblebee’ sections than in arable, fallow, silage, and winter-grazed pasture sections. The availability of bumblebee forage plant flowers was lower in ‘bird and bumblebee’ sections than in silage sections in June, but no other significant differences involving the conservation mix were detected. Plant species in the legume (Fabaceae) family were the most frequently visited by foraging bumblebees. Tufted vetch Vicia cracca was one of a few plant species favoured by bumblebees and was predominantly found in ‘bird and bumblebee’ sections in July-August, although it was not part of the seed mixture. Thirty-one crofts located on Lewis, Harris, the Uists and at Durness were included in the study. The ‘bird and bumblebee’ conservation mix was sown for several bird species and foraging bumblebees, species sown included kale Brassica oleracea, mustard Brassica spp., phacelia Phacelia spp., fodder radish Raphanus sativus, linseed Linum usitatissimum and red clover Trifolium pratense. In addition to the seven management types mentioned, unmanaged pastures were surveyed for foraging bumblebees and bumblebee forage plants along zigzag or L-shaped transects in each croft section once in June, July and August 2008. Foraging bumblebees 2 m either side of transects were identified to species and recorded together with the plant species on which they were foraging. Flowers of all plant species were counted in 0.25 m2 quadrats at 20 or 50 m intervals along the transects.
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