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Environmental Stewardship (ES) is the main mechanism for reversing the decline in farmland birds in England, and includes a range of options designed to provide winter foraging for seed-eating species. We estimated granivorous songbird densities on ES options designed to provide winter food, on farms within the Entry Level (ELS) or Higher Level (HLS) strata of ES. ES Wild Bird Mixtures (WBMs) hosted higher densities and a wider range of granivores than non-ES game covers, although in East Anglia the enhanced HLS WBM was used no more than the basic ELS WBM. In the West Midlands there were low densities of granivores on all WBMs and game covers. The widespread ELS WBM appeared to provide little food for buntings but supported finches, partially through greater weed burdens. There was a weak, non-significant trend for Skylarks Alauda arvensis to make greater use of ELS cereal stubbles than non-ES stubbles, possibly because of post-harvest herbicide restrictions allowing overwinter weed growth. At the field scale, this work demonstrates that although some ES options provide winter food resources for birds, there is limited evidence for additional benefits of Higher Level vs. Entry Level Stewardship to wintering farmland songbirds.
Many farmland bird species have undergone well-documented population declines and range contractions in the UK since the mid-1970s (Gibbons et al. 1993, Fuller et al. 1995, Siriwardena et al. 1998, Gregory et al. 2004). Various facets of agricultural intensification have been major causes of these declines (Chamberlain et al. 2000, Newton 2004), although the precise mechanisms differ spatially and by species due to regional differences in farming systems and ecological differences between species. Reduced availability and abundance of winter seed food has been identified as a key limiting factor of the populations of a suite of declining, resident granivorous farmland species in the UK (Peach et al. 1999, Hole et al. 2002, Gillings et al. 2005, Siriwardena et al. 2007). The switch from spring to autumn sowing of the majority of cereal and oil-seed crops in lowland UK and the increased use and effectiveness of herbicides have led to reductions in both weed seeds and spilt grain, the loss of large areas of weedy, post-harvest stubbles, and a decrease in the abundance and diversity of within-crop and marginal arable weed species (Wilson et al. 2009).
To conserve a range of widespread, formerly common farmland bird species, a variety of habitats is needed to provide nesting and food requirements throughout the farmed landscape. Agri-environment schemes (AESs) are the key delivery mechanism for these (Vickery et al. 2004). AESs across Europe have been criticized for a dearth of clear targets and accompanying monitoring/evaluation (Kleijn & Sutherland 2003), and for delivering limited biodiversity benefits (Kleijn et al. 2001, 2006, Kleijn & Sutherland 2003). However, there is evidence that targeted, well-monitored schemes, backed up by advice to landowners, can produce measurable benefits (Evans et al. 2002, Evans & Green 2007). For example, there is evidence from the Arable Stewardship Pilot Scheme that certain options, some of which have been incorporated into the successor Environmental Stewardship (ES), can provide resources for a range of widespread but declining species (Critchley et al. 2004, Pywell et al. 2004a, 2004b), including birds (Bradbury et al. 2004, Stevens & Bradbury 2006). At a population level, provision of weedy cereal stubbles and invertebrate-rich grassland, via the Countryside Stewardship Scheme (CSS), led to an increase in the population of the Cirl Bunting Emberiza cirlus of 83% in 6 years on CSS land, while numbers on surrounding non-CSS land remained stable (Peach et al. 2001).
ES was launched in England in 2005 by Natural England (the UK government conservation agency for England) and is a multi-objective AES comprising two elements: Entry Level Stewardship (ELS), in which land managers are paid for simple conservation landscape improvement measures, is open to all English farmers in receipt of Single Farm Payment subsidy; Higher Level Stewardship (HLS) involves more complex land management targeted at farm-specific environmental features (e.g. habitats and species) and entry is competitive. The success of ES in delivering its targets and its future development is informed by an evaluation programme, following a clearly defined model, as outlined by Kleijn and Sutherland (2003). As part of the evaluation, studies are being conducted to assess the efficacy of both ELS and HLS in providing habitats that are used by feeding and nesting birds (including this study) and in increasing farmland bird populations (e.g. Davey et al. 2010).
ES has a number of options that allow farmers to provide winter food resources for birds. The most popular are sown plots of so-called ‘Wild Bird Mixtures’ (WBMs – mixes of seed-bearing crops) and the leaving of cereal stubbles through the winter (covering 2784 agreements on 3459 ha and 3237 agreements on 43 791 ha in England in July 2006, around 0.76% of all land under ES: Natural England unpubl. data). Various versions of these options are available to agreement holders (Natural England 2008a, 2008b). ELS options tend to require less management, cost less to implement and therefore attract less remuneration than those available to HLS farmers (the ethos behind ES is that farmers are recompensed for income foregone by taking land out of production and into conservation measures). ELS options may also be included as part of an HLS agreement (Natural England 2008b). HLS options generally require additional management and are targeted at priority species.
This paper reports on a study to measure the comparative efficacy of measures that aim to provide winter seed resources for widespread granivorous bird species. We compare granivore densities on basic ELS WBM and stubble options (EF2/3 and EF6), with their more complex, targeted HLS counterparts (HF12 and HF15), and their non-ES equivalents (game cover, comprising dense stands of cover crops provided over the winter to provide shelter and food to gamebirds; and rotational cereal stubbles, post-harvest stubbles retained until conditions are suitable for establishing the next crop, usually in mid-winter and usually subject to post-harvest herbicide treatments).
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In the context of a subsidy-based AES, maximizing the efficacy of conservation measures is vital to achieve the best and the most cost-effective conservation outcomes. Therefore, basic ELS options should perform better than habitats already commonly present on farmland, and meet the expectations laid out in the management guidelines. Those options for which additional premiums are paid should perform proportionately better again. Although it has proved difficult to draw conclusions about the use of cover crops and stubbles at various levels of ES intervention by the three target species of HLS (because their numbers, even on targeted farms, were too low), this study has demonstrated some positive outcomes of ES options for a broader suite of granivorous species, including two of the three target species and other species of similar conservation concern (Eaton et al. 2008). The fact that target species were not found on HLS farms to the extent that the FEPs indicated suggests that the targeting process on Higher Level farms has not been successful, and management aimed at species will not be benefitting them if they are not finding these resources. In this case, revision and strengthening of the FEP process may be needed for more successful targeting. The FEP and advisory resources available to farms entering the scheme have increased in availability and quality in more recent years since this study was carried out (pers. obs.). Alternatively, the frequency of winter visits in this study may not have been sufficient to detect mobile species at low densities. This may be true for Tree Sparrow, which is known to range widely in winter (Calladine et al. 2006).
In the autumn-sown cereal-dominated East Anglian region, where agricultural intensification has resulted in winter food shortages for granivores (Shrubb 2003, Wilson et al. 2009), WBM options held significantly higher densities of granivores compared with non-ES game covers. Granivore densities in ELS and HLS WBM did not differ significantly, although there was a trend for higher densities in HLS. Shortage of overwinter seed resources are equally important in the pastoral-dominated agriculture in the WM, with the loss of arable components of mixed farming and the switch from hay making to silage production (Shrubb 2003, Wilson et al. 2009). Clearly WBMs should be important in this context (Parish & Sotherton 2008), but the use of ES and game covers were all at an equally low level. Far fewer granivores were encountered on WM sites, and WBMs and game cover were less common, suggesting that WBMs are not providing a better food resource than game covers in this region. It should be a priority of future ES recruitment in this area to increase the uptake of these options as well as to develop methods of increasing the food potential of the prevalent pastoral methods (e.g. Buckingham & Peach 2006).
Variation in bird density and the composition of bird flocks between seed-crop type probably reflect observed differences in the composition and abundance of seed between ELS and HLS WBMs and game covers. Whilst ELS WBMs were catering for small seed-eating Carduelis finches (mostly of low conservation concern) and Reed Buntings, HLS WBM was providing food for the red- and amber-listed Tree Sparrow, Yellowhammer and Corn Bunting. Therefore, there may be a resource provision gap between ELS and HLS WBMs. More and better advice to ELS farmers about the composition of their WBM plots to meet local needs may redress this and make bunting food more widely available (there is no compulsion to include cereals in the ELS WBM mixes (EF2/3 –Natural England 2008a), and buntings are known to favour this food source; Perkins et al. 2008). It is possible that in amalgamating individual granivorous species’ counts into a larger functional ‘Granivores’ grouping for analyses, variation in species composition across farms, clusters or regions on the basis of local landscape factors may have been masked. However, our comparison of flock composition with cover crop type seems to indicate some systematic variation in this respect, although it cannot be taken as definitive.
Weed cover of ELS WBM plots is an indicator not just of increased availability of small-seed food (likely to benefit Linnets and Goldfinches particularly, Campbell et al. 1997), but also of a sparser crop. Our vegetation data suggest that total vegetation cover is less on HLS than ELS WBMs, but this was very variable (our unpubl. data). This may be because there is no yield measure as part of WBM prescriptions, and therefore no incentive to the farmer to ensure good seed yield or crop establishment (Perkins et al. 2008). However, as access to the crop is particularly important for buntings and sparrows, which prefer to feed on the ground (Campbell et al. 1997), and food detectability is improved in shorter or sparser vegetation (Whittingham & Markland 2002, Butler & Gillings 2004), the density of WBM swards should be controlled (by sowing rates or row widths) if the resources provided are to be utilized effectively by their target species, particularly in the cereal components of 1-year mixes targeted at buntings (Perkins et al. 2008). However, this may also facilitate ease of access for other, non-target species (such as Wood Pigeons Columba palumbus), which may deplete resources rapidly, or encourage rapid resource depletion by target species, affecting the persistence of the resource. Solutions to these issues are likely to be found at a local scale, and thus highlight the provision of sound local advice to land managers.
Overall, the WBM results suggest that while there were trends for higher densities and more species of conservation concern to occur in HLS than ELS, they were not necessarily significant differences. On the strength of our results, it is unclear whether the extra management, and targeting, of HLS-enhanced WBMs is worthy of the increased administration costs to the scheme in providing consistent extra benefit. However, the relatively low sampling intensity of this study has not definitively tested this.
Skylarks were found at higher densities in ELS stubbles than non-ES stubbles. This was a weak statistical relationship, and may be the result of low sampling intensity. It is well established that post-harvest stubbles, without broad-spectrum herbicide, can allow substantial weed growth, and some seed setting through the winter (Buckingham et al. 1999). This can provide seed food for granivores (Bradbury et al. 2008, Wilson et al. 2009), and also ‘green’ food for species such as Skylarks, whose diet is known to contain non-seed plant material (Green 1978). Additionally, substantial weed growth may provide extra crypsis benefits for Skylarks, which prefer some cover for roosting and feeding (Butler et al. 2005). Non-ES stubbles tend to be shorter lived, as they are often ploughed in before the end of the year to allow frost action on the soil and to suppress grass weeds. Even if they persist long into the winter, standard practice tends to lead to early application of herbicide post-harvest to suppress weeds. Our sample of HLS reduced herbicide stubbles (HF15) was very small, as this option currently has low uptake. Our results suggest that bird use of this option may be low. One explanation is that because of the reduced herbicide input of this option, farmers tend to place it in fields with known low weed burdens, therefore reducing the amount of food available to birds. However, the cause remains unclear and further work is necessary to make any definitive assessment of this option.
There appears to be some difference in the efficacy of the ELS stubble option (EF6) dependent on whether it is managed under an ELS or HLS agreement. HLS EF6 stubbles attract more granivores and Skylarks compared with the same management on ELS farms. This may be the result of different rotations or other farm-wide practices or a difference in the execution of the same prescription by different farmers. HLS farmers are afforded specific management advice as part of scheme entry, and we cannot exclude the possibility that they may also spend more time on ES prescriptions than their ELS counterparts. Different, pre-agreement cropping patterns or management on farms entering HLS compared with those in ELS may have resulted in either greater weed seed banks in the soil or less effective or reduced weed control in the preceding crop. Alternatively, HLS farms may, by the nature of the scheme, be in areas where the habitat is better suited to target (and non-target) species, and this may explain the greater usage of ELS stubbles on HLS farms. However, the ELS stubble option appears to attract more Skylarks and granivores than non-ES stubbles. This will be increasingly important after the loss of compulsory set-aside (Vickery et al. 2008) and help in improving the quality of arable pockets in the grass-dominated West Midlands (Robinson et al. 2001). These results reiterate the low level of food provision of non-ES stubbles, particularly critical in the current situation of the loss of arable land-use (Robinson et al. 2001) and of rotational set-aside in the west of England (Vickery et al. 2008).
These results only examine bird densities using crops, and allow no inferences about the effect of these on bird populations through time. The aim of ES is to increase and sustain wild bird populations (and particularly those which have undergone recent declines) through the deployment of such options in the agricultural landscape. Therefore, ongoing work is needed to reveal if usage and spatial distribution of such seed-rich habitats is sufficient to influence birds at a population level (Siriwardena et al. 2006).
Furthermore, the longevity of food resources supplied by such seed-rich habitats is of crucial importance and there is already much evidence that a ‘hungry gap’ exists in much English farmland towards the end of the winter (Siriwardena et al. 2008). Certainly, most of the overwinter stubbles surveyed in this study are unlikely to fill this gap; even if they maintain seed resources throughout their life, they will not survive much past the middle of February (the earliest permissible ES stubble cultivation date is 15 February, Natural England 2008a, 2008b, 2010) to allow establishment of spring-sown crops. A new ES extended stubble option (EF22) has become available in 2010, which will remain largely unsprayed (apart from localized treatment of injurious weed species) and uncultivated until at least mid-August (Natural England 2010), and will contribute towards bridging this gap. Although WBMs within ES, particularly 2-year plots, are much more likely to remain into the spring, seed loss is likely to be almost complete by this time for most sown species (Siriwardena et al. 2008) and our observations tend to confirm this. Some cereal components (most notably Triticale) have been developed for, and are promoted on, their ability to retain seed through the winter, and have been observed to do so in WBMs in Scotland (Perkins et al. 2008). This reinforces the conclusion that to benefit declining species, and particularly buntings, ELS WBMs should contain a cereal component, and enhanced WBMs should be encouraged more within HLS agreements.
Davey et al. (2010) found few indications of success of ELS in influencing farmland bird numbers positively at landscape scale, which they attributed to factors operating at various scales. Option quality at an individual farm scale and resource density within the landscape were cited as potential reasons for lack of success. Our results tend to echo this, and although ELS winter food options do show some improvement over the non-ES food sources available, it is uncertain whether they exist at either great enough density, or are of sufficient quality, to affect a change in the fortunes of declining farmland granivores. In this context, it is concerning that HLS options were generally no more effective than the more widespread ELS ones. It seems likely that their quality is similarly inconsistent. Moreover, the question of their effectiveness at improving the conservation status of the scarcer target species remains unanswered. Clearly, the provision of resources at the farm scale is important to these species, but the availability of the resources at a wider landscape scale may well be important, and not influenced by HLS. Thus even for target species, the effectiveness of HLS will be tempered by that of ES in total, especially for wide-ranging species such as Tree Sparrow. Because these species have become so localized in some regions, their scarcity makes their use of particular habitats in relation to fixed features (ES plots) harder to quantify. It is to be hoped that the examination, currently underway, of target species’ trends on farms of different ES levels will inform this question more.
In the current economic climate, the resources available for AESs are likely to become ever more tightly squeezed between the demands of food-security based agricultural policy and competing state and European-wide demands for funding. Therefore, it is imperative that ES can demonstrate fitness for purpose and value for money. To that end, the feedback from monitoring will be vital in addressing shortcomings in resource provision and improving option implementation (Kleijn & Sutherland 2003). It is also important to acknowledge that the impact of ES measures will take time to be realized, with the attendant lag in population responses to environmental change. ES should be viewed through this prism, and both individual options and the schemes should be afforded time to ‘mature’ and for ecological responses to become evident (Davey et al. 2010). The farms studied here had only been subject to ES management for 2 years before monitoring began. Therefore, the continued monitoring currently forming part of the same programme is more likely to detect songbird responses to management as the scheme progresses. It is therefore imperative that monitoring and scheme evolution remain a continuous iterative process, and that ES is given adequate continued support to prove its financial and biodiversity worth (Kleijn et al. 2001, 2006, Kleijn & Sutherland 2003).