Practical management solutions for birds on lowland arable farmland

Transcription

1 Ecology and Conservation of Lowland Farmland Birds 105 Practical management solutions for birds on lowland arable farmland NIGEL D. BOATMAN 1, CHRIS STOATE 1 & P. NICHOLAS WATTS 2 1 Allerton Research & Educational Trust, Loddington House, Loddington, Leicestershire, LE7 9XE, UK 2 Vine House Farm, Deeping St Nicholas, Spalding, Lincolnshire, PE11 3DG, UK Habitat management techniques currently used or proposed on lowland arable and mixed farmland are reviewed, and practical examples described as implemented on two contrasting farms in the East Midlands of England. Management to provide nesting habitat, food during the breeding season and food during winter are considered. Changes in bird numbers resulting from conservation management are recorded, and the cost of, and incentives for, such management are discussed. The population declines and range contractions among lowland farmland birds over the last three decades are well documented (Fuller et al. 1995, Siriwardena et al. 1998). Agricultural intensification is considered to be the major factor causing most of these declines, but because many changes in agriculture and management of the countryside have occurred simultaneously, it is often not clear which specific factors have been most important for a particular species. Fuller et al. (1995) suggested that the reduction in spring sowing (and consequent loss of crop stubbles overwinter), simplification of crop rotations, intensification of grassland management and increased use of agrochemicals were likely to be particularly significant. Gillings & Fuller (1998) concluded that habitat loss (e.g. hedgerow removal) was of secondary importance to habitat degradation (e.g. depletion of food supplies by pesticides and other changes in crop husbandry). For some species, the mechanisms causing population declines have been indicated by autecological studies (e.g. Grey Partridge Perdix perdix, Potts 1986; Corncrake Crex crex, Green & Stowe 1993; Cirl Bunting Emberiza cirlus, Evans & Smith 1994; Stone-curlew Burhinus oedicnemus, Green & Griffiths 1994), leading to targeted conservation action (Aebischer et al. 2000). For others, mechanisms have been proposed, but not proven, based on examination of species ecology and changes in farming practice (e.g. Campbell et al. 1997). Practical habitat management, based on research or empirical observation, can often give insights into the way birds interact with their environment and provide clues to their conservation requirements. Management implemented to benefit one species may also provide benefits for others sharing the same habitats/ecological requirements (e.g. food, nest sites). In this paper we review habitat management techniques currently used on lowland arable and mixed farmland, with particular reference to research at The Allerton Research and Educational Trust s study farm in Leicestershire, plus practical experience of conservation measures from a contrasting farm in the Lincolnshire fens. STUDY SITES AND MANAGEMENT The Loddington Estate is a 333-ha mixed (but predominantly arable) farm in the east of Leicestershire on clay soil, growing winter cereals, oilseed oape, beans and linseed. The 43 ha of permanent pasture are grazed mainly by sheep, and there are 28 ha of woodland including a disused railway embankment. Hedgerows are the predominant field boundary type, many of which also have adjacent ditches. The Loddington Estate is the site of the Allerton Project, a partnership between the Allerton Research and Educational Trust and The Game Conservancy Trust (GCT), whose aim is to research, develop and demonstrate techniques for integrating game and wildlife conservation with viable commercial farming (Boatman & Stoate 1999). Vine House Farm is a 118-ha arable farm on organic clay loam soil in the Lincolnshire fens, owned and managed by P. N. Watts. It is one of several farms that make up a total of 680 ha of land farmed by P.N. Watts in Deeping Fen. A variety of arable crops are grown including potatoes, sugar beet, winter wheat, oilseed rape, linseed, peas and grass for seed. There is little woodland other than two small (0.6 ha) spinneys, and fields are bounded by drainage dykes. There is only one established hedge on the farm. Conservation management on the Loddington Estate is primarily directed towards wild game species, but an extensive monitoring programme for other bird species is in place. At Vine House Farm, a variety of management practices have been implemented to cater for the perceived needs of resident species as determined by direct observation.

2 106 Ecology and Conservation of Lowland Farmland Birds REQUIREMENTS OF FARMLAND BIRDS Most studies of farmland birds highlight the importance of one or more of the following requirements for survival: nesting habitat, food supplies during the breeding season and food supplies during winter, and for convenience the management techniques discussed will be classified under these three headings. The effects of predation will not be considered here as they are reported elsewhere (Stoate & Thompson 2000). Nesting habitat Hedgerows Many farmland birds nest in hedgerows (Lack 1992). A number of studies have been carried out on birds and hedgerows, reviewed by O Connor & Shrubb (1986), Lack (1992) and Lakhani (1994); a further study carried out at Swavesey in Cambridgeshire has been recently published by Sparks et al. (1996). These studies are generally based on surveys of bird occurrence, and there is a lack of experimental studies of the effects of hedgerow management and work relating management to nesting density and breeding success of individual species. At Loddington, hedges are cut in late winter to avoid nest disturbance as well as to allow birds a chance to eat hedgerow berries, providing that field boundaries are accessible at this time of year. Herbaceous vegetation Whilst most hedge-nesting birds nest in hedgerow shrubs, for some the adjacent herbaceous component is more important. Both species of partridge regularly nest in herbaceous vegetation in field boundaries. For example, Aebischer et al. (1994) found that 65% of radio-tagged Grey Partridges nested in field margins; others nested in crops or grass fields. Rands (1988) found that Grey Partridges chose to nest where dead grass, leaf and bramble were greater than in surrounding vegetation; Red-legged Partridge Alectoris rufa nests were also linked to the amount of Common Nettle Urtica dioica. Aebischer et al. (1994) found that the vegetation around Grey Partridge nest sites was significantly denser at heights above 20 cm than around randomly chosen non-nest sites, and there were also differences in botanical composition, the vegetation around nests being characteristic of mesotrophic rough grasslands. At Loddington, field boundaries are managed to contain at least 1 m of uncut tussocky vegetation each side of the hedge. Field boundaries with such extensive vegetation contained more Yellowhammer Emberiza citrinella and Whitethroat Sylvia communis territories per km of field boundary than without such vegetation (Stoate & Szczur 1994). Mean nest heights were 0.28 m for Yellowhammer and 0.48 m for Whitethroat, compared to 1.26 m for Chaffinch Fringilla coelebs. Yellowhammers often built on the ground in rank grass and herbs, whilst Whitethroats nested low down in herbs and brambles. The selection of field boundaries by nesting Whitethroats was found to be related to the width of herbaceous vegetation in the field boundary (Stoate 1999). The percentage of randomly selected field boundaries in the Loddington area occupied by breeding Whitethroats was greatest at a width of around 2.5 to 3.0 m; when less than 1 m of herbaceous vegetation was present, no Whitethroats were found. Territory establishment for Yellowhammers was related to ditch depth and herb height; hedge height had a negative influence on territory establishment for both species (Stoate 1999). At Vine House Farm, Yellowhammers have been discovered laying their first eggs as late as 1 August. Such nests are likely to be at risk from flail mowing, which often commences as early as July on many farms. In contrast to Partridges, field margins are not preferred nesting habitats for Pheasants Phasianus colchicus (Hill & Robertson 1988). At Loddington, of 60 hen Pheasants radiotagged between 1996 and 1998, only 15% nested in field margin habitat, the remainder nesting in crops, setaside, woodland etc. (S. Bence unpubl.). Crops Crops can also provide nesting habitat for passerines. In Deeping Fen, two thirds of Reed Bunting Emberiza schoeniclus nests are in oilseed rape. Prior to harvest, oilseed rapecrops are either swathed or sprayed with a desiccant, to promote ripening; 50% of Reed Buntings with a second brood may still have young in the nest at this time. A joint study with the British Trust for Ornithology, in 1996, found that all nests that were still active were destroyed by swathing. In contrast, desiccation did not affect any of the nests and all broods fledged successfully in desiccated crops (Burton et al. 1999). Desiccation effectively gave the birds an extra days to fledge before harvest. Skylarks Alauda arvensis nest on the ground in open habitats, including crops. However, territory density and breeding success are higher in set-aside (Poulsen et al. 1998, Wilson et al. 1999). Skylarks favour set-aside at both Loddington and Vine House Farm (see below). Drainage ditches Some Reed Warblers Acrocephalus scirpaceus also raise their first brood in oilseed rape, but most Reed and Sedge Warblers Acrocephalus schoenobaenus nest in reedy ditches. They are therefore vulnerable to flail mowing of ditches

3 Ecology and Conservation of Lowland Farmland Birds 107 that is carried out immediately after harvest, from July onwards on many farms. Drains in Deeping Fen were formerly cut twice a year; as a result of discussions with the local drainage board, only one side of each main drain is now cut each year. This has resulted in at least one pair of Reed Warblers per 50 m of drain, plus Sedge Warblers at one pair every 400 m over a length of 16 km. Artificial nest sites Nest-site availability can be a limiting factor, particularly for hole-nesting species including owls (Newton 1994). Erection of nest boxes for Barn Owls Tyto alba at Vine House Farm in 1985 led to two pairs nesting in Increasing the number of nest boxes to 20 (including other farms in Deeping Fen) in 1998 resulted in nine nesting pairs of Barn Owls in 1998 and eleven in During this period farming has become more intensive. Since 1993, grass margins 2 m wide have been established under the Countryside Stewardship Scheme around some fields, which could have provided additional foraging area, but only for five of the pairs as the others nested on different farms. Food during the breeding season Long-term research on the Grey Partridge has identified the importance of invertebrates in chick diet (Potts 1986), and chick survival is related to the availability of certain insect taxa (Potts & Aebischer 1991). Hen Grey Partridges with broods feed predominantly in cereal crops, particularly near the edges (Green 1984). The introduction of herbicides reduced the availability of insect food in cereals by removing the weed host plants (Southwood & Cross 1969), and the more recent widespread use of insecticides in cereals has had a further impact on food availability, reducing chick survival on average by a third (Aebischer & Potts 1998). Experimental studies in which pesticide use was reduced on the outer 6 m of cereal crops showed increased chick survival compared to areas with fully sprayed crops (Rands 1985, 1986). The evidence for indirect effects of pesticides has recently been reviewed by Campbell et al. (1997), who concluded that the Grey Partridge provided the best example. However, many other declining farmland birds also feed their chicks on invertebrates, including Skylark (Jenny 1990, Poulsen & Aebischer 1995), Corn Bunting Miliaria calandra (Aebischer & Ward 1997, Brickle & Harper 1999), Cirl Bunting (Evans et al. 1997) and Yellowhammer (Stoate et al. 1998). Campbell et al. (1997) concluded that indirect effects of pesticides were possible for at least 11 out of 24 declining farmland bird species. Minimising the impact of insecticide use There is little doubt that the summer use of insecticides is the most damaging farm operation in terms of its potential effects on chick survival (Aebischer 1990, Aebischer & Potts 1998). Several approaches are used to minimise possible impacts of insecticide use: i) Damage thresholds At both Loddington and Vine House Farm, insecticides are used in summer only where pest insects exceed damage thresholds (e.g. Oakley & Walters 1994). Careful monitoring has resulted in insecticides being applied to control cereal aphids (Hymenoptera: Aphididae) only once during the sixyear life of the Allerton Project (in 1995), in spite of numbers being close to the threshold level in other years. In 1994, when concern about the effects of Wheat Blossom Midge Contarinia tritici swept the country, only a small part of one field was treated. Examination of field edges revealed numbers above threshold, but these rapidly declined over the first few metres into the crop to below threshold levels. The same trend was observed at Vine House Farm, which was one of very few farms in the area that did not spray for Wheat Blossom Midge at all that year. ii) Selective products Should insecticide use be necessary, the most selective product available should be chosen (Anon. 1997). In the case of the 1995 aphid outbreak at Loddington, pirimicarb was used at two-thirds rate, which nevertheless gave good control of aphids. Nontarget groups such as ladybirds (Coleoptera: Coccinellidae) were observed feeding on the wheat ears several days after spraying. Experimental work has shown that pirimicarb is much more selective than either organophosphates or pyrethroids, though some effects on non-target groups can still occur (Cole & Wilkinson 1984, Sotherton 1990). Analysis of data from the GCT s Sussex Study on pesticide use and invertebrate abundance detected no effect of pirimicarb use, whereas most invertebrate groups were much less abundant in fields treated with pyrethroids or organophosphates (Ewald & Aebischer 1999). A similar policy is applied at Vine House Farm. When an aphicide is needed, pirimicarb is used at reduced rate (down to one third of the recommended rate), rather than the cheaper but broad-spectrum alternatives such as cypermethrin or dimethoate. iii) Buffer zones Certain insecticides, such as dimethoate and some synthetic pyrethroids, have a label restriction on use within 6 m of the crop edge in summer to protect adjacent habitats, though wider buffer zones of at least 12 m have been recommended for insecticides (Davies et al. 1993). At Loddington, no insecticides are sprayed within 6 m of any crop edge, or 12 m in the case of

4 108 Ecology and Conservation of Lowland Farmland Birds cereals in summer, with the aim of preserving a reservoir of untreated invertebrates to recolonise the rest of the field (Duffield & Aebischer 1994). iv) Natural predators Natural enemies of pests can limit population growth and maintain numbers below thresholds (Wratten & Powell 1991). Many predatory invertebrates are also food for farmland birds. Oakley et al. (1998) found that years of high aphid incidence were characterised by a lower than average incidence of natural enemies. One way of encouraging such predators is to provide additional resources in terms of non-crop habitat. Many polyphagous predators (beetles Coleoptera, especially Carabidae and Staphylinidae, and spiders Araneae) overwinter in field boundaries (Sotherton 1984) from which they disperse into crops in spring. Thomas et al. (1991) proposed the creation of linear islands of habitat within large fields to create additional overwintering cover so that dispersal could occur from the field centre as well as from the margins. These midfield ridges, sown with tussock-forming grasses, have become known as beetle banks. As a result of Thomas s research, Cocksfoot Dactylis glomerata and Yorkshire Fog Holcus lanatus were recommended for sowing on beetle banks. However, work at Loddington has shown that Yorkshire Fog fails to persist in competition with Cocksfoot, and Red Fescue Festuca rubra is a more suitable companion. It is also cheaper and easier to obtain. Experimental work at Loddington has provided evidence that polyphagous predators emigrating from beetle banks can reduce aphid numbers on winter wheat (Collins et al. 1997). Beetle banks also provide potential nesting cover, and attract large numbers of small mammals, thus providing hunting areas for Kestrel Falco tinnunculus and Barn Owl. At Loddington they form part of mid-field set-aside strips, 20 m wide, managed to provide a range of habitats so that (i) nesting birds have ready access to good feeding habitat, and (ii) the set-aside payment can be claimed on the land taken up by the beetle bank. Maintaining/increasing invertebrate abundance Certain measures can be taken to ensure that numbers of those invertebrates favoured as chick food remain at a high level. These include undersowing, provision of conservation headlands and set-aside management. i) Undersowing One of the most important invertebrate groups in the diet of Grey Partridge chicks comprises the larvae of sawflies Symphyta (Potts 1986), which have also been found to be significant dietary components of young Corn Buntings (Aebischer & Ward 1997). Aebischer (1990) showed that sawfly densities in West Sussex were related to the proportion of cereal fields that were undersown, and densities of Grey Partridges (Aebischer & Potts 1998) and Corn Buntings (Aebischer & Ward 1997) were also highest where this form of farming was practised. Unfortunately, undersowing is now very little used as a method of establishing grass, and its revival is likely only if grant aid is available, as in the South Downs Environmentally Sensitive Area and the pilot Arable Stewardship Scheme. It is not used at Vine House Farm because there are no livestock, and hence no need to establish grassland. At Loddington, the sheep graze permanent pasture fields, which are unsuitable for arable cropping; establishment of leys would be uneconomic as arable crops are a much more profitable use of the suitable fields, and there would also be considerable expenditure on fencing and provision of water for the stock. Also, undersowing works best with spring cereals and the soil type at Loddington is not suited to these. For these reasons, undersowing is not a practical form of management on these two farms. ii) Conservation Headlands The Conservation Headland technique originated with the work of Rands (1985, 1986), who showed that reducing pesticide use on the outer few metres of cereal fields can increase the survival of Grey Partridge chicks. Its development has been described by Sotherton (1991) along with research into the benefits for other forms of wildlife, which include Blue-headed Wagtail Motacilla flava (de Snoo et al. 1994), butterflies (Dover et al. 1990, de Snoo et al. 1998), small mammals (Tew et al. 1992) and arable flora (Wilson 1994). In order to make the concept acceptable to farmers, it was necessary to draw up agronomic guidelines for management to achieve the objectives with minimal effect on crop yield and quality (Boatman & Sotherton 1988, Anon. 1997). The technique involves the use of selective herbicides to control Black-grass Alopecurus myosuroides, Wild Oats Avena spp. and Cleavers Galium aparine, avoiding the use of broadspectrum compounds (Boatman 1987, Boatman et al. 1988, Anon. 1997). Until recently conservation headlands were considered to be most applicable on lighter soils, being too difficult to implement on clay soils where Blackgrass and Cleavers are most abundant. However, the advent of new chemistry has allowed the refinement of the technique to achieve the necessary balance between conservation advantage and cost on the heavy soils at Loddington, with yield losses amounting to less than 0.5% of the crop (Boatman et al. 1999). Monitoring at Loddington has shown that there is a greater cover of broad-leaved annual weeds in

5 Ecology and Conservation of Lowland Farmland Birds 109 conservation headlands than where headlands are fully sprayed (Boatman et al. 1999), but because the benefits to other forms of wildlife had been studied comprehensively elsewhere, research effort at Loddington has concentrated on the benefits of more recently developed forms of management. At Vine House Farm, conservation headlands have been applied in all wheat crops since In 1999 an opportunity arose to compare two fields having conservation headlands with an intervening field belonging to a neighbour, which had no conservation headlands, though the reed cover in the boundary ditches was similar. On the two fields with conservation headlands there was a pair of Reed Warblers to every 30 m of ditch, and they raised on average 3.0 chicks per nest, compared to a pair every 42 m rearing 2.4 chicks per nest in the field without conservation headlands. iii) Set-aside Rotational set-aside can provide insect-rich feeding areas, but most farmers spray it with a broadspectrum herbicide in April or early May to control weeds. Although research has shown that spraying can be delayed until early June without prejudicing levels of weed control (Boatman et al. 1995), this is still too early for gamebirds and second clutches of other species. Naturally regenerated set-aside left for more than one year is favoured as nesting and foraging habitat by Skylarks (Poulsen 1996, Wilson et al. 1997, Poulsen et al. 1998), but its value for other species is likely to decline as vegetation density increases. At Loddington, brood-rearing cover mimicking a conservation headland is created under the Wild Bird Cover option on long-term set-aside, by sowing a cereal-based crop mixture. This includes the stipulated 5% of legumes (e.g. Red Clover Trifolium pratense) to attract insects as well as naturally occurring annual weeds. At Vine House Farm, set-aside stubbles were left to regenerate naturally until July between 1992 and Over this period the number of Skylark territories increased from 4 to 16. Since then there has been less set-aside and it has been sown with Wild Bird Cover (see below). Whilst this has benefited other species, Skylark numbers have dropped back to 1990 levels. In contrast, at Loddington, Skylark numbers have remained relatively constant between 1992 and 1998 (36 breeding territories in both years). In 1992, when there were 49 ha of naturally regenerated setaside in three fields, 47% of Skylark territories were associated with set-aside. In 1998, with 21.5 ha of setaside in field margins and mid-field strips, mostly sown to Wild Bird Cover, 71% of Skylark nests were associated with set-aside. Availability of seeds and grain A few farmland species feed their young entirely on seeds, e.g. Linnet Carduelis cannabina (Moorcroft & Wilson 2000) and Turtle Dove Streptopelia turtur (Murton et al. 1964), but others will supplement their chicks diet with unripe grain (Stoate et al. 1998, Brickle & Harper 1999). At Vine House Farm, only 10% of Corn Buntings nest early enough to achieve a second brood. The earliest broods are fed mainly carabid beetles; later a wider variety of insects are fed. In 1994, 20 Corn Bunting nests were mapped and nesting dates recorded. All the early nests were within 300 m of winter barley, the earliest crop to ripen. Females from these nests were regularly observed feeding on unripe barley grain, and sometimes also feeding it to nestlings. Food during winter Stubbles Of nine resident farmland birds that have declined by more than 50% in the last 25 years, eight feed on seed in winter (Evans 1997). Wilson et al. (1996) found that stubbles were preferred feeding areas for Grey Partridge, Skylark, Linnet and Reed Bunting. Donald & Evans (1994) found that Corn Buntings preferred stubbles and unimproved grassland to winter cereals and improved grass. Weedy stubbles held twice as many birds as clean stubbles. Stubbles appear to be particularly significant for Cirl Buntings Emberiza cirlus; Evans & Smith (1994) found that stubbles and fallow fields were the preferred feeding habitat in winter, and this species also showed an association between stubble weediness and bird usage. Increasing the amount of stubble available to Cirl Buntings has been a major factor in the threefold increase in their British population between 1988 and 1995 (Evans 1997, Aebischer et al. 2000). The area of stubble has declined dramatically in recent decades as a greater proportion of crops have become autumn-sown, and stubbles have become cleaner as the efficiency of herbicides has increased, so that those stubbles remaining are likely to be of less value for birds. Experience at Loddington has shown that, even when stubbles are present, few birds are found feeding on them. Since 1992 however, set-aside has greatly increased the amount of stubble present in the countryside, with resulting benefits for birds (Henderson & Evans 2000). At Vine House Farm, all fields are ploughed by December because the heavy soil needs to weather in order to ensure a good tilth for spring-sown crops. The only stubbles that remain over winter therefore are those that are set-aside. Game crops/wild Bird Cover Observations indicate that game cover and pheasant feeders are often used by feeding birds in winter (e.g.

6 110 Ecology and Conservation of Lowland Farmland Birds Table 1. Relative use of Wild Bird Cover crops by seed-eating birds at Loddington. a) Comparison of main plots (i.e. set-aside strips) and farm crops: KALE1 = first-year kale, KALE2 = second-year kale, CEREAL = cereal-based crop mixture, CROP = farm crop. b) Comparison of sub-plots sown with different companion crops within second-year kale strips on set-aside: KALE = Kale only, KT = Kale +Teasel, KEP = Kale + Evening Primrose, KP = Kale + Parsnip; only bird species making significantly greater use of second-year kale, and for which adequate data were available, are considered. >>> = statistically significant difference at P < Bird species Rank order Statistical significance Main plots and farm crops Chaffinch KALE2 >>> KALE1 > CEREAL > CROP Λ = 0.00, P < Goldfinch KALE2 >>> KALE1 > CEREAL > CROP Λ = 0.00, P < Linnet KALE2 >>> KALE1 > CEREAL >>> CROP Λ = 0.00, P < Reed Bunting KALE2 >>> KALE1 > CEREAL >>> CROP Λ = 0.15, P < Greenfinch KALE2 > KALE1 > CEREAL >>> CROP Λ = 0.00, P < Yellowhammer CEREAL >>> KALE1 > KALE2 > CROP Λ = 0.10, P < 0.01 Subplots within second-year kale Chaffinch KEP > KT > KALE > KP Λ =0.29, P < Goldfinch KT > KEP >>> KALE >>> KP Λ =0.00, P < Linnet KALE >>> KP > KEP > KT Λ = 0.25, P < 0.01 Brickle 1997, Stoate & Szczur 1997). The value of set-aside can also be increased by growing unharvested crop mixtures on it, under the Wild Bird Cover option. At Vine House Farm, crops have been grown specifically for birds since Crops grown away from farm buildings attracted large numbers of Woodpigeons Columba palumbus, so they are now grown only in small fields around farm yards. Up to 800 finches and buntings have been observed in one field, with Corn Buntings and Reed Buntings, in particular, attracted to wheat. A 3x500-m strip of burdock Arctium sp. is also grown, which feeds 300 Goldfinches Carduelis carduelis for four months. Systematic walks across all habitats on the farm at Loddington were carried out over the winters of 1996/97 and (over a larger area) 1997/98 to assess their use by feeding birds. In 1996/97 it was only possible to include Wild Bird Cover mixtures based on cereals or Kale Brassica napus, but in 1997/98, set-aside strips were available that had been sown with Kale but split into sub-plots containing Teasel Dipsacus fullonum, Evening Primrose Oenothera biennis, Parsnip Pastinaca sativa or no companion. It was also possible to compare these second-year Kale strips (i.e. with seed present) with first-year Kale, which had not yet flowered. The use of the various habitats by finches and buntings in relation to their availability is shown in Fig. 1. In both winters, little use was made of farm crops. Yellowhammers favoured cereal-based Wild Bird Cover and, later in the winter, switched to grain at gamebird feed sites, whilst other species made most use of mixtures based on second-year Kale. Compositional analysis (Aebischer et al. 1993) was used to analyse crop use in 1997/98, in two stages. They first examined the relative use of four major habitat categories (first-year Kale, second-year Kale, cereal-based Wild Bird Cover and commercial crops). The second investigated the relative use of the four sub-groups within the second-year Kale category (Kale with Teasel, Kale with Evening Primrose, Kale with Parsnip or Kale only) for those species making significantly more use of second-year Kale than other crops in the first analysis. The analysis enabled crops Habitat use (%) Habitat use (%) 100% 80% 60% 40% 20% 100% 80% 60% 40% 20% 0% 0% Farm crop Triticale Kale Feed site Hedge Available Yellowhammer Greenfinch Reed Bunting 1st-year Kale 2nd-year Kale Kale/Evening Primrose Kale/Teasel Kale/Parsnip Cereal Feed site Hedge Farm crop Available Greenfinch Linnet Goldfinch Chaffinch Reed Bunting Yellowhammer Figure 1. Habitat use by feeding finches and buntings at Loddington in winter 1996/97 (top) and 1997/98 (bottom). Kale and Cereal refer to kale- or cereal-based Wild Bird Cover mixtures on set-aside; Available refers to proportional availability of habitats on the farm.

7 Ecology and Conservation of Lowland Farmland Birds 111 to be placed in rank order of preference, and identified significant differences between crops where these occurred (Table 1). Yellowhammers made significantly more use of cereal-based Wild Bird Cover than any other habitat. Chaffinch, Goldfinch, Linnet and Reed Bunting all made significantly greater use of second-year Kale than other habitats, though Linnet and Reed Bunting along with Greenfinches Carduelis chloris significantly preferred all types of Wild Bird Cover to farm crops (Table 1a). Greenfinches made most use of second-year Kale but also used first-year Kale, feeding on Sunflowers Helianthus annuus sown in mixture with the Kale. Sufficient data were available to compare second-year Kale subgroups for Chaffinch, Goldfinch and Linnet (Table 1b). Goldfinches made significantly greater use of plots containing Teasel and Evening Primrose, whilst Linnets preferred plots containing Kale only. Seed samples were collected from the Wild Bird Cover crops containing mixtures based on second-year Kale in September, November and January. By January, virtually all seed had been exhausted (Fig. 2). Goldfinch numbers were correlated with the abundance of Teasel and Evening Primrose in October (r 16 = 0.63, P < 0.01) and November (r 16 = 0.447, P = 0.06), but no other relationships between bird numbers and seed abundance approached significance. Observations indicated that bird numbers were influenced by plot location and adjacent habitats (e.g. proximity of hedgerows, trees etc.). Numbers of finches and buntings observed through the winter are shown in Fig. 3. Greenfinches, Goldfinches and Linnets were seen in similar or (for Greenfinch) increasing numbers between October and December, but in January and February were virtually absent. Yellowhammer and Chaffinch, however, were observed throughout the winter. Earlier work has shown that Yellowhammers in particular make use of game feeding stations once the seed supplies in the Wild Bird Cover were exhausted (Stoate & Szczur 1997). Changes in bird numbers Although the management techniques described are believed to address factors contributing to declines in farmland birds, as already noted, for many species the causes of their decline are not yet completely understood. In the absence of such information, monitoring of bird populations is one way of measuring the success of conservation management, though where a package of measures has been implemented, it is not possible to distinguish with certainty which technique(s) have been of greatest value. Territory mapping was conducted for most bird species present at Loddington during the breeding season in 1992, before active management began and in 1998, in the sixth Seeds ( 000 per m 2) ± se Kale Teasel Evening Primrose Parsnip September November January Figure 2. Availability of seeds on seedheads of crops in kale-based mixtures at Loddington between September 1997 and January Number of birds recorded Greenfinch Linnet Goldfinch Chaffinch Yellowhammer Reed Bunting Oct Nov Dec Jan Feb Mar Figure 3. Numbers of finches and buntings recorded feeding in different winter months at Loddington. Breeding territories Skylark Wren Dunnock Robin Blackbird Song Thrush Whitethroat Blackcap Willow Warbler Blue Tit Great Tit Chaffinch Greenfinch Linnet Yellowhammer Figure 4. Numbers of breeding territories of the most abundant passerines at Loddington in 1992 (baseline, before conservation management) and 1998 (sixth year of conservation management). year of management. Fig. 4 shows the breeding abundance of some of the most common passerines in these two years. Most species increased between 1992 and 1998, some substantially. Yellowhammer and Skylark have maintained their numbers at Loddington, though Yellowhammers have declined nationally by 25.5% and Skylarks by 14.4% between 1992 and 1998 (British Trust for Ornithology Common Birds Census). In common with other nationally declining species, both are present at higher densities at Loddington than in nearby comparison

8 112 Ecology and Conservation of Lowland Farmland Birds areas (C. Stoate unpubl.). The two principal gamebird species at Loddington, Pheasant and Red-legged Partridge, also increased from 37 to 78 and from 2 to 16 breeding territories respectively. At Vine House Farm, Reed Buntings have trebled in numbers up to one pair per 16 ha. Yellowhammers, which are present only at a very low density in the area as a whole, have increased from zero to six breeding pairs. Skylark numbers have been maintained at one pair per 6 ha where 20-m grass set-aside strips are present. Reed Warblers have increased from zero to 25 pairs per km of drain, which has led to an increase in Cuckoos Cuculus canorus to five pairs along 8 km of drain. Barn Owl numbers have also trebled over fifteen years. CONCLUSION Although the causes of farmland bird declines are not fully understood for many species, most studies suggest that factors affecting availability of nesting habitat, food for chicks in summer and/or food for adults in winter are likely to be important. Practical measures to address these requirements, based on research and observation, have led to maintenance or increases in breeding densities of a number of species, including nationally declining ones, at both study sites. These case studies show what can be achieved on conventionally managed (as opposed to, for example, organic) commercial farmland with relatively minor adjustments to farming practice. Such conservation management is not, however, entirely cost-free. For example, at Loddington the profit foregone from conservation in the cropped area of the farm (not including hedgerows, woodlands etc.) has been calculated at between 1,782 and 3,825 between 1994 and This includes costs of managing set-aside, conservation headlands, field margin grass strips and beetle banks. In some years extra land was set aside above the minimum requirement. For example, in 1997 and 1998 when the requirement was 5% of the arable area, the set-aside area at Loddington was around 8% of the arable area. An allowance was therefore made for the extra 3% of land that could have been cropped. In other years, when the requirement was 10%, this allowance was not necessary. If this allowance is discounted, the conservation costs remained relatively constant, at between 1,634 and 1,866 over the period Further details are given in Anon. (1999), Boatman et al. (1999) and Boatman & Stoate (1999). If set-aside were withdrawn as an obligatory measure, these costs would rise considerably. Whilst some farmers, particularly those interested in wild game conservation, might be prepared to cover at least some of these costs, the majority will be prepared to spend only a limited amount of time and money on wildlife conservation. Grant aid from Agri-Environment Schemes is likely to become increasingly important in stimulating environmentally beneficial management. The Countryside Stewardship Scheme has provided grants for grass margins for some years, and support for some other measures, e.g. conservation headlands, is available in certain Environmentally Sensitive Areas and in the Scottish Countryside Premium Scheme. In the present context, the advent of the pilot Arable Stewardship Scheme is particularly relevant. 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