Agriculture, Ecosystems and Environment 112 (2006) 283–290 www.elsevier.com/locate/agee
Effects of the Arable Stewardship Pilot Scheme on breeding birds at field and farm-scales Danae¨ K. Stevens *, Richard B. Bradbury Royal Society for the Protection of Birds, The Lodge, Sandy, Bedfordshire SG19 2DL, UK Received 30 November 2004; received in revised form 17 July 2005; accepted 27 July 2005 Available online 23 September 2005
Abstract In the short- to medium-term, agri-environment schemes are potentially the key mechanism for reversing farmland bird declines across Europe. The Arable Stewardship Pilot Scheme (ASPS) was designed to test the delivery of resources by a suite of management options for a range of farmland taxa, in two lowland farmland regions of England (East Anglia and West Midlands). The impact of ASPS on breeding farmland birds was tested in a replicated farm-scale experiment, in which changes in numbers of breeding birds over 5 years were compared between scheme and control farms. Additionally, the impact of specific ASPS options on breeding bird distribution was assessed at the fieldscale, using data collected after the options had been deployed for 5 years. At the field-scale, presence/absence of both field nesting and boundary-nesting species was associated with the presence of certain ASPS options. Many of these responses can be explained in terms of abundance of/access to nest sites or invertebrate/seed food resources provided by the ASPS options. However, despite showing significant positive responses at the field-scale, most species showed no response at a farm-scale. Between-year changes were significantly more positive on scheme than control farms for only three species in East Anglia and one species in West Midlands. The importance of these results is discussed with respect to the value of further research on the scale of options required to produce farm-scale effects. # 2005 Elsevier B.V. All rights reserved. Keywords: Agri-environment; Sustainable farming; Farmland birds; Countryside; Biodiversity targets
1. Introduction Recent population declines and range contractions of farmland birds in the UK are well-documented (Fuller et al., 1995; Gregory et al., 2003; Siriwardena et al., 1998) and these declines are associated with intensification of agricultural production (Chamberlain et al., 2000; Siriwardena et al., 1998). At a European scale, declines of farmland birds within individual countries are correlated with the degree of intensification of farming practice within the country (Donald et al., 2001). An indication of the severity of the problem is the response by the UK Government’s Department for the Environment, Food and Rural Affairs (Defra): a Public Service Agreement (PSA) target to reverse the decline in farmland birds by 2020, as measured by the * Corresponding author. Tel.: +44 1588 650197; fax: +44 1588 650197. E-mail address: danae.stevens@rspb.org.uk (D.K. Stevens). 0167-8809/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2005.07.008
combined population trends of 20 species (the ‘Farmland Bird Index’; Gregory et al., 2003). Agri-environment schemes are a key mechanism for reversing declines in farmland biodiversity, such as birds (Vickery et al., 2004). In England, the Arable Stewardship Pilot Scheme (ASPS) started in 1998, to test the delivery of a range of land management practices (‘options’: Table 1) for farmland species of various taxa (Anon, 2001). Specific bird targets included provision of invertebrates and seed rich habitats for food and provision of breeding sites for groundnesting birds, such as lapwing Vanellus vanellus L. and skylark Alauda arvensis L. A monitoring project ran from 1998 to 2001. Although this revealed a number of positive responses of plants and invertebrates to specific scheme options, there were few positive farm-scale responses by vertebrates (Anon, 2001; Bradbury and Allen, 2003). A second monitoring project started in autumn 2002, at the end of the first 5-year agreements, to test whether, given more
284
D.K. Stevens, R.B. Bradbury / Agriculture, Ecosystems and Environment 112 (2006) 283–290
Table 1 Options available in the Arable Stewardship Pilot Scheme including supplemental options Option 1 Sub-option 1A Sub-option 1B
Sub-option 1A + B
Sub-option 1C Sub-option 1A + C
Option 2 Sub-option 2A Sub-option 2B Sub-option 2A + B Option 3 Sub-option 3A Sub-option 3B Option 4 Sub-option 4A Sub-option 4B Sub-option 4C Option 5
Overwintered stubble Reduced herbicide use in cereal or linseed, followed by overwintered set-aside stubble Overwintered cereal or linseed stubble, followed by shallow spring cultivation and spring/summer fallow Reduced herbicide use in cereal or linseed, followed by overwintered stubble and spring/summer fallow Overwintered stubble followed by spring crop Reduced herbicide use in cereal or linseed, followed by overwintered set-aside stubble and a spring crop Undersown spring cereal Overwintered stubble, followed by undersown spring cereal Undersown spring cereal, followed by grass ley Overwintered stubble, followed by undersown spring cereal and grass ley Crop margins with no summer insecticide Conservation headlands Conservation headlands with no fertilizer applications Grass field margins by natural regeneration or sown grasses (4–12 m wide) Beetle banks Uncropped wildlife strips (4–12 m wide) Wildlife seed mixtures
time, bird populations had responded. Numeric responses by wintering birds and breeding success responses by grey partridge Perdix perdix L. have been reported elsewhere (Bradbury et al., 2004; Browne and Aebischer, 2003). The resurvey of the ASPS sites presented an opportunity to collect high-resolution data on the spatial distribution of bird territories, using territory-mapping techniques, for construction of associative bird-habitat models (Fielding and Haworth, 1995). Construction of these models would enable resolution of whether: (a) farm-scale responses of birds to ASPS could be attributed to particular ASPS options; (b) failure to detect a response at the farm-scale masks a response at a smaller, option-scale; (c) there was no response to the scheme at either scale.
2. Methods ASPS scheme options were established in autumn 1998 in two regions of England, East Anglia (comprising approximately, 2200 km2 and covering parts of south Cambridgeshire, west Suffolk, north Essex and north Hertfordshire) and the West Midlands (comprising approximately 1500 km2 in east Shropshire and west Staffordshire). These were selected to test the scheme options over a range of arable farming
types, soil types and biodiversity resources, for example, the West Midlands was characterised by more mixed farming and heavier soils. Assessment of the farm-scale effect of the scheme on birds was achieved by comparison of responses on farms in the scheme with those on ‘control’ farms that had not entered the scheme. Scheme site selection was not random, because almost all sites which entered the schemes, which were of sufficient size, were surveyed. Control sites were selected by approaching farmers near to scheme farmers. Hence, selection of control sites was also probably not entirely random, as there would inevitably be some small biases in which control sites were amenable to being used. A transect methodology, similar to that of the Breeding Bird Survey (BBS) (Gregory and Baillie, 1998) was adopted for the farm-scale survey, in order to gain a whole-farm density estimate. At each farm, a survey route of approximately 2000 m was selected, along field boundary features. To avoid double-counting of birds, the route never returned to within 200 m of a previous part of its course. Where a 2000 m route could not be achieved because of the small size of the farm, the longest possible length was used. Surveys were carried out during the first breeding season after ASPS options were established (1999) and were repeated again in summer 2003. In East Anglia, 23 scheme farms and 18 control farms were surveyed in both years. In West Midlands, 24 scheme and 19 control farms were surveyed in both years. Two recording visits were made to each farm in each year. The first was in the early part (from early-April to mid-May) and the second in the late part (from mid-May to late-June) of the breeding season. Counts began at 06:00–7:00 h and all birds seen or heard along the survey route were recorded, in distance categories estimated at right angles to the transect line. The distance categories were: (i) within 25 m; (ii) between 25 and 100 m; (iii) over 100 m; (iv) in flight. Flying birds that were actively hunting (raptors, hirundines) in one of the distance bands were recorded in that distance band, rather than as flying individuals. Juvenile birds recorded in the field did not contribute to the analysis (following Gregory and Baillie, 1998). Thus, all records related to breeding or potentially breeding, adults. Surveys were not conducted in periods of heavy rain, strong wind or poor visibility and routes were reversed between visits to minimise any effects of time of day on the presence and detectability of birds. A check was made that any effects observed were not simply the result of a differential between-year change in the proportion of surveyed fields that were arable on scheme and control sites. This was done by binomial logistic regression, specifying number of arable fields as the response variable and total number of fields as the binomial denominator and testing the interaction between farm-type and year. For the option-scale analysis, breeding birds were mapped using territory-mapping methodology (Marchant et al., 1990) at eight ASPS sites in each region in 2003. Sites were visited eight times between 1 April and 31 July and on each visit, the location of all territorial or nesting activity
D.K. Stevens, R.B. Bradbury / Agriculture, Ecosystems and Environment 112 (2006) 283–290
was registered onto a farm map. Over all visits, the combined registrations of the more numerous species formed ‘clusters’, resolving the locations of territories. Standard rules (Bibby et al., 2000) were used to determine how many registrations in a cluster were sufficient to resolve a territory of each species. Once the position of territories was resolved, the territory was allocated to a habitat unit, where a habitat unit was a field for field-nesting species or a field boundary for boundary-nesting species. Boundary habitat units comprised any contiguous length of field boundary between intersections with other field boundaries. If the boundary class changed between intersections, it was sub-divided into separate units (Bradbury et al., 2000). If a territory was shared between more than one habitat unit, each unit was allocated an equal fraction of the territory (Bradbury et al., 2000). Detailed habitat data were collected for each habitat unit, mostly on the first visit. Some species may be more likely to settle preferentially in locations that provide late winter/spring food resources, as well as breeding resources and so data on winter habitat were also collected. The list of habitat variables is given in Table 2. Habitat variables included ASPS options and features that had previously been shown to be associated with one or more species. Field sizes and boundary lengths were calculated from digitised maps using MapInfo Professional 6 (MapInfo Corporation, 2000). The mean census area per farm was 125 ha in the West Midlands and 169 ha in East Anglia. The farm-scale analysis was based on the change in maximum count of a species on each farm between years. Following Gregory and Baillie (1998), birds recorded beyond 100 m and birds in flight, apart from those actively hunting, were excluded. Variation in maximum count was assessed in generalised linear models (GLMs), specifying a Poisson error structure and a log link and controlling for overdispersion. Study site identity and region were included as fixed effects and the natural log of transect length was specified as an offset, to account for the probability of higher counts with longer transects. Separate models were constructed for each ASPS region, testing the effect of the interaction between farm-type: (1) control and (2) scheme and year: (1) 1999 and (2) 2003. Because the between-year change was expected to be more positive on scheme farms, statistical tests were one-tailed (a = 0.05); for tests based on the x2 statistic with 1 d.f., the probability level was determined by treating its square root as a one-tailed ztest. Bonferroni corrections were applied to significance values, to account for multiple tests on the same data-set. To conduct the option-scale analysis, GLMs were constructed that correlated variation in distribution of birds between habitat units to variation in characteristics of those units. As most data were highly dispersed, with many zero counts in individual habitat units, the count data were reduced to presence/absence per habitat unit and modelled using binary logistic regression. Field size/boundary length terms were included in the models, to control for the greater probability of birds occurring by chance in bigger fields/
285
Table 2 Independent habitat variables included in the model-building exercise for the option-scale analyses Variable Field-nesting species Crop type
Seed-providing option
Reduced pesticide use
Grass margin index Beetle bank Uncropped wildlife strip index Boundary-nesting species Boundary type
Seed-providing option
Reduced pesticide use
Maximum grass margin
Fallow
Uncropped wildlife strip
Definition 13-Level factor: winter cereal, spring cereal, winter rape/brassicas, spring rape, silage, pasture, rough grass, set-aside, option 1B, sugar beet/other root crops, legumes, bare till, potatoes Two-level factor: wildlife seed mixture/stubble present (1) or absent (0) in field in previous winter Two-level factor: conservation headland or reduced herbicide use in current crop (1) or not (0) Proportion of field perimeter with grass margin Two-level factor: beetle bank present (1) or absent (0) in field Proportion of crop perimeter with uncropped wildlife strip Three-level factor: managed woody vegetation (1); unmanaged woody vegetation (2); boundary not dominated by woody vegetation (3) Two-level factor: wildlife seed mixture/ stubble present (1) or absent (0) in adjacent field in previous winter Two-level factor: conservation headland or reduced herbicide use in any crop adjacent to boundary (1) or not (0) Maximum width of adjacent grass margin (either side of boundary), in metres Two-level factor: set-aside or option 1B in any field adjacent to boundary (1) or not (0) Two-level factor: uncropped wildlife strip adjacent to boundary (1) or not (0)
Site, region and ln field size/boundary length were included in all models.
longer boundaries. ‘Site’ and ‘region’ were included in the models as fixed effects, to control for unmeasured variation between sites and between regions. It was decided that site could not be declared as a random effect, as choice of sites was not strictly random. For all species, a suite of candidate models was compared using Akaike’s information criterion (AIC). Site, region and field size/boundary length were included in all models. The remaining terms in each model consisted of all possible combinations of up to six variables, for both field-nesting species models and boundary-nesting species models. All of these variables related to specific ASPS options (Table 2). AIC differences were calculated for all models, relative to the model with the smallest AIC value, then Akaike weights were calculated for each model (Burnham and Anderson, 2002; Whittingham et al.,
286
D.K. Stevens, R.B. Bradbury / Agriculture, Ecosystems and Environment 112 (2006) 283–290
Table 3 Farm-scale breeding bird responses to ASPS, giving the effect on maximum count per year of the interaction between farm-type and year Variable
Blackbird Turdus merula Bullfinch Pyrrhula pyrrhula Carrion crow Corvus corone Chaffinch Fringilla coelebs Corn bunting Miliaria calandra F Dunnock Prunella modularis Goldfinch Carduelis carduelisF Greenfinch Carduelis chloris F Grey partridge Perdix perdix F House sparrow Passer domesticus Jackdaw Corvus monedula F Lapwing Vanellus vanellusF Linnet Carduelis cannabinaF Meadow pipit Anthus pratensis Mistle thrush Turdus viscivorus Pied wagtail Motacilla alba Reed bunting Emberiza schoeniclusF Robin Erithacus rubecula Rook Corvus frugilegus F Skylark Alauda arvensisF Song thrush Turdus philomelos Starling Sturnus vulgarisF Stock dove Columba oenasF Tree sparrow Passer montanusF Turtle dove Streptopelia turturF Whitethroat Sylvia communisF Woodpigeon Columba palumbusF Wren Troglodytes troglodytes Yellowhammer Emberiza citrinellaF Yellow wagtail Motacilla flavaF
West Midlands
East Anglia
Z
P-value
Scheme effect
Z
P-value
Scheme effect
2.26
NS
Negative
0.28 1.89 3.17 1.33 1.57 0.51 0.1 0.99 0.68 0.41 1.31 4.72 1.27 0.72 1.13 0.1 1.20 0.94 1.08 1.1 0.94 0.89
NS NS NS NS NS NS NS NS NS NS NS <0.001 NS NS NS NS NS NS NS NS NS NS
Positive Negative Negative Negative Negative Positive Positive Negative Negative Positive Negative Positive Negative Negative Positive Positive Positive Negative Negative Negative Negative Negative
1.06 1.01 4.91 0.87 3.60 0.2 1.45 0.27 1.65 2.31 1.33 1.85 0.45 0.17 1.52 0.84 4.58 1.24 2.33 0.92 0.25 2.38 0.69
NS NS <0.001 NS <0.001 NS NS NS NS NS NS NS NS NS NS NS <0.001 NS NS NS NS NS NS
Negative Negative Positive Positive Positive Negative Negative Negative Positive Positive Negative Negative Positive Positive Negative Positive Positive Negative Positive Positive Negative Positive Negative
1.27 0.95 0.82 1.52 0.71
NS NS NS NS NS
Positive Negative Negative Negative Positive
0.35 0.25 0.14 0.1 1.32 2.73
NS NS NS NS NS NS
Negative Negative Negative Negative Positive Positive
F, Farmland Bird Index species.
2005). For each variable, the sum of the Akaike weights of all the models containing that variable were calculated, to give the probability of the variables considered, that variable is contained in the best approximating model. That is, it gives the selection probability for each variable, on a scale from 0 to 1 (Whittingham et al., 2005).
3. Results In the West Midlands, the mean transect length was 2359 m for scheme farms and 2305 m for control farms. In East Anglia, the mean transect length was 2487 m for scheme farms and 2422 m for control farms. At the farmscale, the between-year change was significantly more positive (i.e. a greater increase or smaller decrease) on scheme than control sites, for only three species in East Anglia (carrion crow Corvus corone L., reed bunting Emberiza schoeniclus L. and corn bunting Miliaria calandra L.) and one species (meadow pipit Anthus pratensis L.) in the West Midlands (Table 3). Overall, only 10 of 27 species in the West Midlands and only 14 of 28 species in East Anglia, showed more positive between-year changes on
stewardship than control sites (Table 3). There was no evidence that the amount of arable land surveyed on scheme farms changed between years in a different way to that on control farms (x2 1137 = 0.10, P = 0.7555). In fact, the proportion of surveyed fields that were arable did not differ between years (x2 1138 = 0.01, P = 0.9191) or farm-types (x2 1137 = 1.31, P = 0.2533). Data for the field-scale analysis were collected from 162 fields (total area 996.1 ha) in West Midlands and 94 fields (1354.19 ha) in East Anglia. Of the 256 fields surveyed, 196 were arable and 60 were pastoral. Four field-nesting species (lapwing, corn bunting, skylark and yellow wagtail Motacilla flava L.) were recorded sufficiently frequently to construct models. Due to zero counts in many habitat units, logistic models could not always be successfully fitted for all sites/field types. Therefore, the following models were fitted; lapwing (West Midlands only; present in 12 fields), skylark (arable fields only; present in 137 fields), corn bunting (arable fields only; present in 44 fields). The direction of effect and selection probability for each variable, for each species, are shown in Table 4. For skylarks, there were very high selection probabilities for crop type (0.993; option 1B most selected), presence of
D.K. Stevens, R.B. Bradbury / Agriculture, Ecosystems and Environment 112 (2006) 283–290
287
Table 4 Results of option-scale habitat association modelling for field-nesting species Species
Crop type
Seed-providing option
Reduced pesticide use
Grass margin index
Beetle bank presence
Uncropped wildlife strip index
SP
Effect
SP
Effect
SP
Effect
SP
Effect
SP
Effect
SP
Effect
Corn bunting
0.124
0.334
Positive
0.828
Positive
0.324
Positive
0.307
Negative
0.447
Positive
Lapwing
0.688
0.588
Positive
0.354
Positive
0.266
Negative
0.353
Negative
0.284
Negative
Skylark
0.993
0.980
Positive
0.356
Positive
0.996
Positive
0.314
Positive
0.310
Positive
Yellow wagtail
0.767
3>9>1> 13 > 8 > 11 = 2 > 10 > 4 11 > 9 = 8 = 10 = 1>5=7= 6 > 3 = 2 = 13 9 > 11 > 13 = 8 > 1>4>2 > 10 = 3 9 > 11 = 10 = 3 = 4 = 12 = 1 = 2 = 7 > 5 = 13 =8>6
0.423
Negative
0.303
Negative
0.295
Positive
0.467
Negative
0.321
Negative
SP, selection probability of variable; effect, direction of effect of continuous variables, effect of presence of option relative to absence for categorical variables or relative selection of each category in the case of ‘crop type’: 1, winter cereal; 2, spring cereal; 3, winter rape or other brassicas; 4, spring rape; 5, silage; 6, pasture; 7, rough grass; 8, set-aside; 9, option 1B; 10, sugar beet or other root crops; 11, legumes; 12, bare till; 13, potatoes.
seed-providing option in the field the previous winter (0.980; positive influence on field occupancy) and grass margin index (0.996; positive). All other variables had selection probabilities below 0.4. For lapwings, no variables had high selection probabilities, the highest being crop type (0.688; legumes most selected). Yellow wagtail models also produced no variables with very high selection probabilities, the highest being crop type (0.767; option 1B, most selected). Corn bunting had a reasonably high selection probability for fields with low pesticide inputs (0.828; positive), but no other variable had a selection probability above 0.5. Models for boundary-nesting species were based on data from a total of 986 boundary sections. Eight boundarynesting species were recorded sufficiently frequently to enable models to be fitted: dunnock Prunella modularis L.
(present on 266 boundaries), whitethroat Sylvia communis Latham (241), chaffinch Fringilla coelebs L. (388), greenfinch Carduelis chloris L. (84), linnet Carduelis cannabina L. (60), reed bunting (45) and yellowhammer Emberiza citrinella L. (297). Very few tree sparrows Passer montanus L. were encountered in East Anglia, so models could only be constructed for the West Midlands sites (present on 45 of 678 boundaries). The direction of effect and selection probability for each variable, for each species, are shown in Table 5. Boundary type had a selection probability of over 0.93 for all species except reed bunting. The presence of a seedproviding option next to the boundary in the previous winter had a selection probability of 0.936 for linnet, but was below 0.6 for all other species. Limited pesticide use in fields next to the boundary had a selection probability of over 0.9 for
Table 5 Results of option-scale habitat association modelling for boundary-nesting species Species
Boundary type
Seed-providing option
Reduced pesticide use
Grass margin width
Fallow presence
Uncropped wildlife strip presence
SP
Effect
SP
Effect
SP
Effect
SP
Effect
SP
Effect
SP
Effect
Chaffinch Dunnock Greenfinch Linnet Reed bunting Tree sparrow Whitethroat Yellowhammer
1.000 1.000 0.999 0.936 0.675 1.000 0.932 1.000
1=2:3 2>1:0 2=1:3 1:2:3 3>2=1 1>2:3 1=2:3 1>2:3
0.579 0.355 0.311 0.936 0.302 0.281 0.478 0.487
Positive Positive Positive Positive Positive Negative Positive Positive
0.988 0.431 0.995 0.493 0.756 0.278 0.933 0.998
Positive Positive Positive Positive Negative Negative Positive Positive
0.861 0.407 0.305 0.395 0.494 0.398 1.000 0.941
Positive Positive Positive Positive Positive Negative Positive Positive
0.283 0.280 0.302 0.862 0.284 0.507 0.840 0.320
Negative Positive Positive Positive Negative Positive Positive Positive
0.368 0.343 0.305 0.358 0.998 0.375 0.405 0.535
Positive Positive Positive Positive Positive Negative Positive Positive
SP, selection probability of variable; effect, direction of effect of continuous variables, effect of presence of option relative to absence for categorical variables or relative selection of each category in the case of ‘boundary type’: 1, managed woody vegetation; 2, unmanaged woody vegetation; 3, boundary not dominated by woody vegetation.
288
D.K. Stevens, R.B. Bradbury / Agriculture, Ecosystems and Environment 112 (2006) 283–290
whitethroat, chaffinch, greenfinch and yellowhammer (and 0.756 for reed bunting). Grass margin width had a selection probability of over 0.9 for both whitethroat and yellowhammer (and 0.861 for chaffinch). Fallow had a selection probability of over 0.8 for both whitethroat and linnet, while uncropped wildlife strips had a selection probability of 0.998 for reed buntings.
4. Discussion At the resolution of the option-scale assessment, many associations were detected between both field and boundarynesting species and stewardship options. These associations reflect nest site provision and abundance of/access to food resources, in the form of invertebrates and weeds, which were themselves enhanced by ASPS options (Anon, 2001; Critchley et al., 2004; Pywell et al., 2004a,b). Crop type had a very high selection probability for skylark and reasonably high selection probabilities for lapwing and yellow wagtail. Option 1B and legumes were strongly selected by skylarks, while option 1B, legumes, setaside and sugar beet/root crops were most selected by lapwings. Yellow wagtails selected option 1B above all other field types. Option 1B, the spring–summer fallow preceded by light spring cultivation, was designed to offer a heterogeneous ground surface, making nest detection by predators more difficult and untilled soil, relatively rich in soil invertebrates, such as earthworms (Sheldon, 2002). The response by lapwings, at which the option was primarily targeted, was, therefore, in accordance with expectations. Option 1B also provides short vegetation/bare areas for foraging, a heterogeneous habitat which is favoured by breeding skylarks and yellow wagtails (Bradbury and Bradter, 2004; Donald, 2004). Summer fallow should also provide an abundance of weeds, providing both seed and invertebrate food, which may explain the response by linnets and whitethroats. The apparent selection of legumes and sugar beet/root crops by lapwings may also reflect the availability of bare ground for nesting in these spring-sown crops. If this is the case though, the apparent lack of selection of spring cereals by skylarks and lapwings is surprising and contradicts previous work (e.g. Mason and Macdonald, 2000). In contrast to the other species, corn buntings seem to actively choose dense swards for nesting (A.J. Perkins, personal communication; Brickle et al., 2000) and this is reflected in their habitat selection in this study. The reduced pesticide options (conservation headlands and low input cereals) were highly selected by whitethroats, chaffinches, greenfinches and yellowhammers and to a slightly lesser degree, corn bunting. However, reed bunting showed a relatively strong negative association. These associations could reflect both direct effects of insecticides on invertebrates and herbicides on weeds, as well as indirect effects of herbicides on invertebrates via removal of their plant food sources (Campbell et al., 1997; Potts, 1986). The
conservation headland option has been shown to have a high incidence of dicotyledonous plants compared to sprayed areas (Critchley et al., 2004). Therefore, this should have enhanced nestling–food provision in the form of both weed– seeds, which are fed to nestlings by greenfinches and the invertebrates, which are fed to nestlings by the other species. Previous work has shown that foraging patterns and breeding success of both yellowhammer and corn bunting are influenced negatively by summer insecticide use (Brickle et al., 2000; Morris et al., 2005). The grass margin option was highly selected by both boundary nesters (whitethroats, yellowhammers and to a lesser extent, chaffinches) and skylarks. Grass margins are favoured foraging and nesting habitats for both yellowhammers and whitethroats (Bradbury et al., 2000; Morris et al., 2001; Stoate and Szczur, 2001). In the ASPS, many invertebrate taxa responded positively to this option (Anon, 2001), which would, therefore, be expected to be a source of insects for nestling food. Wide margins can also be used by foraging skylarks (Wilson, 2001) and if field boundaries are low, for nesting. However, it is perhaps more likely that the relationship with skylarks detected here is because margins provide a reservoir of invertebrates, such as carabid beetles, that can colonise field centres (Thomas et al., 1991). Given the selection of grass margins by skylarks, however, it is very odd that no species, including skylark, showed any selection of beetle banks. Uncropped wildlife strips were selected strongly only by reed buntings. Annuals, especially dicotyledonous species, dominated this option (Critchley et al., 2004) and many invertebrate taxa responded positively (Anon, 2001). It is probable, therefore, that the reed bunting response reflected foraging habitat provision. Boundary type had a very high selection probability for all boundary-nesting species except reed bunting, for which it was still reasonably high. Boundaries with hedges were preferred by all species except reed bunting, which probably reflects the fact that this species nests in rank vegetation on the ground (Brickle and Peach, 2004). The selection of hedges in which the woody vegetation was managed through a regular cutting regime (tree sparrow, linnet, yellowhammer), is as observed in many previous studies (e.g. Bradbury et al., 2000; Green et al., 1994; Moorcroft, 2000; Parish et al., 1995). Only, dunnocks selected relatively unmanaged hedges. Fields which contained wildlife seed mixtures or stubble in the previous winter were very strongly selected by skylarks and linnets. Recent work has demonstrated that availability of seed-bearing winter habitats can influence settlement patterns of granivorous birds in summer (Gillings et al., 2005; Whittingham et al., 2005). Despite these option-scale associations, farm-scale effects were only detected for three species in East Anglia and one species in the West Midlands. Given that farm-scale effects were analysed for 28 species, these results suggest that the apparent success in delivery of birds at the optionscale is not translated into success at the farm-scale. In
D.K. Stevens, R.B. Bradbury / Agriculture, Ecosystems and Environment 112 (2006) 283–290
contrast, effects at both option and farm-scales were found for key seed-providing options and wintering granivorous birds, at least in the West Midlands (Bradbury et al., 2004). In East Anglia, winter effects on seed-eating birds were observed at the option-scale, but not at the farm-scale. In the breeding season, many species are territorial and show a despotic distribution of territories, effectively excluding each other from habitat. In this case, greater coverage of an option (no matter what quality) within each farm might be required to produce a detectable farm-scale effect on many species. Overall, the results documented here and previously (Bradbury et al., 2004) suggest that the types of options deployed in the ASPS can, as they were designed to, provide the nest site and food requirements of a range of species. However, it needs to be determined how big an area scheme habitats need to cover, for example under the new Environmental Stewardship Scheme, and how frequent they must be at the landscape-scale, to generate positive population responses, ultimately as shown in detectable increases in the Farmland Bird Index and the delivery of the farmland bird PSA target (Vickery et al., 2004). Acknowledgements Many thanks to all the landowners who granted access to survey their farms and to Dave Allen for help with the first survey. We are very grateful to all who helped with fieldwork, including Guy Anderson, Chris Bailey, Simon Cockayne, Steve Coney, James Darke, Diana de Palacio, Jim Dustow, Chris Keeling, Will Kirby, Andy Mayo, Charles Morrison, Barry O’Dowd, Richard Penson, Stuart Priestley and David Wright. Nicholas Aebischer gave statistical advice. Tony Morris, Paul Donald, Andy Evans, Phil Grice, Richard Winspear, Jerry Wilson and two anonymous referees gave helpful comments. This work was funded by Defra and English Nature.
References Anon, 2001. Ecological evaluation of the Arable Stewardship Pilot Scheme: 1998–2000. Report to UK Ministry of Agriculture, Fisheries and Food by ADAS Consulting Ltd., The Centre for Land Use and Water Resources Research, University of Newcastle, EGI and GCT. Bibby, C.J., Burgess, N.D., Hill, D.A., Mustoe, S.H., 2000. Bird Census Techniques, second ed. Academic Press, London. Bradbury, R.B., Allen, D.S., 2003. Evaluation of the impact of the pilot UK arable stewardship scheme on breeding and wintering birds. Bird Study 50, 131–141. Bradbury, R.B., Bradter, U., 2004. Habitat associations of yellow wagtails on lowland wet grassland. Ibis 146, 241–246. Bradbury, R.B., Kyrkos, A., Morris, A.J., Clark, S.C., Perkins, A.P., Wilson, J.D., 2000. Habitat associations and breeding success of yellowhammers on lowland farmland. J. Appl. Ecol. 37, 789–805. Bradbury, R.B., Browne, S.J., Stevens, D.K., Aebischer, N.J., 2004. Fiveyear evaluation of the impact of the pilot Arable Stewardship scheme on birds. Ibis 146 (Suppl. 2), 171–180.
289
Brickle, N.W., Peach, W.J., 2004. The breeding ecology of reed buntings Emberiza schoeniclus in UK farmland and wetland habitats in lowland England. Ibis 146 (Suppl. 2), 69–77. Brickle, N.W., Harper, D.G.C., Aebischer, N.J., Cokayne, S.H., 2000. Effects of agricultural intensification on the breeding success of corn buntings. J. Appl. Ecol. 37, 742–755. Browne, S.J., Aebischer, N.J., 2003. Arable Stewardship: impact of the pilot scheme on the brown hare and grey partridge after five years. Final Report to Defra on Contract Ref. RMP1870vs3. Burnham, K.P., Anderson, D.R., 2002. Model Selection and Multimodel Inference. Springer, New York. Campbell, L.H., Avery, M.I., Donald, P., Evans, A.D., Green, R.E., Wilson, J.D., 1997. A review of the indirect effects of pesticides on birds. JNCC Report No. 227. Joint Nature Conservation Committee, Peterborough, UK. Chamberlain, D.E., Fuller, R.J., Bunce, R.G.H., Duckworth, J.C., Shrubb, M., 2000. Changes in the abundance of farmland birds in relation to the timing of agricultural intensification in England and Wales. J. Appl. Ecol. 37, 771–788. Critchley, C.N.R., Allen, D.S., Fowbert, J.A., Mole, A.C., Gundrey, A.L., 2004. Habitat establishment on arable land: assessment of an agrienvironment scheme in England, UK. Biol. Conserv. 119, 429–442. Donald, P.F., 2004. The Skylark. T. & A.D. Poyser, London. Donald, P.F., Green, R.E., Heath, M.F., 2001. Agricultural intensification and the collapse of Europe’s farmland bird populations. Proc. R. Soc. Lond. B Biol. Sci. 268, 25–29. Fielding, A.H., Haworth, P.F., 1995. Testing generality of bird-habitat models. Conserv. Biol. 9, 1466–1481. Fuller, R.J., Gregory, R.D., Gibbons, D.W., Marchant, J.H., Wilson, J.D., Baillie, S.R., Carter, N., 1995. Population declines and range contractions among lowland farmland birds in Britain. Conserv. Biol. 9, 1425– 1441. Gillings, S., Newson, S.E., Noble, D.G., Vickery, J.A., 2005. Winter availability of cereal stubbles attracts declining farmland birds and positively influences breeding population trends. Proc. R. Soc. Lond. B. Green, R.E., Osborne, P.E., Sears, E.J., 1994. The distribution of passerine birds in hedgerows during the breeding season in relation to characteristics of the hedgerow and adjacent farmland. J. Appl. Ecol. 31, 677– 692. Gregory, R.D., Baillie, S.R., 1998. Large-scale habitat use of some declining British birds. J. Appl. Ecol. 35, 785–799. Gregory, R.D., Eaton, M.A., Noble, D.G., Robinson, J.A., Parsons, M., Baker, H., Austin, G., Hilton, G.M., 2003. The state of the UK’s birds 2002. The RSPB, BTO, WWT and JNCC, Sandy. Marchant, J.H., Hudson, R., Carter, S.P., Whittington, P., 1990. Population Trends in British Breeding Birds. British Trust for Ornithology, Tring. Mason, C.J., Macdonald, S.M., 2000. Influence of landscape and land-use on the distribution of breeding birds in farmland in eastern England. J. Zool. Lond. 251, 339–348. Moorcroft, D., 2000. The causes of the decline in the linnet Carduelis cannabina within the agricultural landscape. Unpublished D.Phil. Thesis. University of Oxford. Morris, A.J., Whittingham, M.J., Bradbury, R.B., Wilson, J.D., Kyrkos, A., Buckingham, D.L., Evans, A.D., 2001. Foraging habitat selection by yellowhammers (Emberiza citrinella) in agriculturally contrasting regions in lowland England. Biol. Conserv. 101, 197–210. Morris, A.J., Wilson, J.D., Whittingham, M.J., Bradbury, R.B., 2005. Indirect effects of pesticides on breeding yellowhammer (Emberiza citrinella). Agric. Ecosyst. Environ. 106, 1–16. Parish, T., Lakhani, K.H., Sparks, T.H., 1995. Modelling the relationship between bird population variables and hedgerow, and other field margin attributes. Part II: abundance of individual species and of groups of similar species. J. Appl. Ecol. 32, 362–371. Potts, G.R., 1986. The Partridge: Pesticides, Predation and Conservation. Collins, London. Pywell, R.F., Warman, E.A., Sparks, T.H., Greatorex-Davies, J.N., Walker, K.J., Meek, W.R., Carvell, C., Petit, S., Firbank, L.G., 2004a. Assessing
290
D.K. Stevens, R.B. Bradbury / Agriculture, Ecosystems and Environment 112 (2006) 283–290
habitat quality for butterflies on intensively managed arable farmland. Biol. Conserv. 118, 313–325. Pywell, R.F., Warman, E.A., Carvell, C., Sparks, T.H., Dicks, L.V., Bennett, D., Wright, A., Critchley, C.N.R., Sherwood, A., 2004b. Providing foraging resources for bumblebees in intensively farmed landscapes. Biol. Conserv. 121, 479–494. Sheldon, R.D., 2002. Factors affecting the distribution, abundance and chick survival of the lapwing (Vanellus vanellus). Unpublished Ph.D. Thesis. Harper Adams University College and Open University. Siriwardena, G.M., Baillie, S.R., Buckland, S.T., Fewster, R.M., Marchant, J.H., Wilson, J.D., 1998. Trends in the abundance of farmland birds: a quantitative comparison of smoothed common birds census indices. J. Appl. Ecol. 35, 24–43. Stoate, C., Szczur, J., 2001. Whitethroat and yellowhammer nesting success and breeding distribution in relation to field boundary vegetation. Bird Study 48, 229–235.
Thomas, M.B., Wratten, S.D., Sotherton, N.W., 1991. Creation of ‘‘island’’ habitats in farmland to manipulate populations of beneficial arthropods: predator densities and emigration. J. Appl. Ecol. 28, 906– 918. Vickery, J.A., Bradbury, R.B., Henderson, I.G., Eaton, M.A., Grice, P.V., 2004. The role of agri-environment schemes and farm management practices in reversing the decline of farmland birds in England. Biol. Conserv. 119, 19–39. Whittingham, M.J., Swetnam, R.D., Wilson, J.D., Chamberlain, D.E., Freckleton, R.P., 2005. Habitat selection by yellowhammers Emberiza citrinella on lowland farmland at two spatial scales: implications for conservation management. J. Appl. Ecol. 42, 270–280. Wilson, J.D., 2001. Foraging habitat selection by skylarks on lowland farmland during the nestling period. In: Donald, P.F., Vickery, J.A. (Eds.), The Ecology and Conservation of Skylarks Alauda arvensis. RSPB, Sandy, pp. 129–138.