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FACTORS CONTRIBUTING TO INCREASING BIRD POPULATIONS ON ARABLE FARMLAND IN ENGLAND I. HENDERSON One of the most important conservation issues effecting bird populations in lowland Europe over the last 30 years has been the widespread loss of structural complexity on farmland, at both landscape and field scales (Benton et al., 2003; Donald et al., 2006). In arable areas, simplified rotations, through the replacement of a variety of spring crops with winter-sown cereals (Fig. 1) have been coupled with technological advances in crop management to attain greater control of competitive plants, invertebrates and disease (Chamberlain et al., 2000). Together these factors have contributed to well-documented declines in the abundance and variety of many plants and animals associated with farmland, and not least birds (Fig. 2) (Siriwardena et al., 1998). Examples include an overall reduction in the availability of food for seed-eating and insectivorous birds and a lack of suitable nest sites for species such as lapwings (Vanellus vanellus) (Sheldon et al., 2002) and skylarks (Alauda arvensis) (Donald, 2004).
Figure 1. The switch from winter to spring cereal Demands for higher standards in the UK, for the protection of biodiversity, soils and raw materials (Curry et al., 2002), have driven programmes aimed at underpinning a UK government commitment to reverse declining bird populations on farmland by the year 2020 (as measured by the official Farmland Bird Index (FBI). In doing so, the mechanisms that influence bird densities around farmland (nest sites summer food and winter food) need to be understood and addressed through modified management practices on a geographic scale large enough to effect positive and relative changes in national bird populations. Ways that this could be achieved, either for a massive uptake of key management prescriptions and/or for large areas of crops and crop rotations to make basic and fundamental contributions to habitat and food provision.
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Figure 2. Trends in populations of wild birds 1970–2004. Large-scale solutions Two recent long-running research projects indicate that the capacity exists to increase bird densities on modern arable farmland, given sufficient willingness, financial support and promotion. The first, named ‘Saffie’ (Sustainable Arable Farming For an Improved Environment), tested the integrated effects of field margin management with in-field management of crops swards to create better access for birds in to the commonest summer crop – winter wheat. The second, known as the ‘Colworth project’, tested the importance of crop complexity and set-aside management to birds in and around crops across the farm. The Saffie project was a five-year project finishing in 2006. The project explored ways to maintain efficiency on farms while providing improved conditions for birds, plants and invertebrates associated with the commonest and most widespread crop – winter wheat, to affect change over as wide a geographical area as possible. Measures were taken to: 1. Manipulate the agronomy of wheat to increase biodiversity. 2. Manage margin vegetation to maximise biodiversity. 3. Identify ‘best’ crop and ‘best’ margin management practices. For birds, the SAFFIE data show that a combined effect of UP and field margins, was particularly affective in increasing the numbers of many bird species using wheat fields, and in affecting positive change in the numbers of breeding territories and nesting attempts associated with wheat. This response was consistent also for Biodiversity Action Plan species, for which farmland recovery in their populations is most needed. SAFFIE was able to demonstrate that a simple combination of in-field and field margin management techniques
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was enough to effect significant increases in the numbers of birds associated with wheat fields. Bird densities and territories were consistently higher (1¡3– 2¡8 times) in fields with margins (4% of field area) and two undrilled patches per hectare, compared to a normal conventional crop. In field margins, birds responded to both higher beetle and spider abundances and complex swards with bare ground. In wheat crops, birds responded mainly to the presence of undrilled patches (large-scale open ground). The effect of creating foraging access in dense crops and field margins was therefore the single most important management action to affect a significant increase in bird densities and breeding territories for both field and boundary nesting species. Skylarks nested at higher density and foraged for longer in such fields, so increasing foraging efficiency when provisioning young (Figs 3 & 4)
Figure 3. Effects of crop complexity: Skylarks
Figure 4. Effects of combined whole-field complexity
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Suffolk Natural History, Vol. 44 Average changes at Colworth 2000 to 2005 Species Grey Partridge Skylark Linnet Reed Bunting Yellowhammer Lapwing Yellow Wagtail Tree Sparrow Corvids & raptors
change +66% +15% +21% +31% +20% Breeding attempt Began breeding Absent to regular =/+
At Colworth, a rapid and sustained population increase among a wide range of bird species occurred in contrast to local regional trends for the same species. At Colworth, 70% of the increase occurred within three years of the initial establishment of the experiment, including species of high conservation concern that increased on average, by 30%. (but 300% for grey partridge and 46% for skylarks in peak years). Also, three BAP species began breeding on the site that had not been present in the early years (ie. lapwing, yellow wagtail and tree sparrow). The results show that bird species typical of arable farmland can be responsive to suitable farm-scale changes in habitat and food provision. They also demonstrated that it is possible to significantly increase the carrying capacity of modern, commercially viable arable farmland for birds, where a large enough proportion of land contributes as habitat. This was achieved by using crops mosaics to create habitat options at the farm scale,
Figure 5. Increase in the number of breeding pairs at Colworth 2000 to 2005
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alongside the appropriate reduced herbicide management of set-aside. Bird densities were on average 2·6 times higher in field types other than winter wheat, and the replacement of 34% winter wheat with other field types (e.g. oilseed rape spring wheat, peas and set-aside) was enough to explain the increase in bird densities, especially during the first three years of the study. Higher bird densities were associated with oilseed rape (whitethroat, Cardueline finches and buntings) and late, May/June-sprayed set-aside (skylark and buntings) and to a lesser extent, vining peas (insectivores). Winter wheat supported more skylarks than oilseed rape or wheat stubble (early, April-sprayed set-aside). Overall, the experiment demonstrated that, at a scale of roughly 1-km2, the carrying capacity of farmland could be increased. The difference between late-sprayed and early-sprayed set-aside was the greatest source of contrast in bird abundances, and contributed to peak population levels for skylarks and buntings on the site. The delayed-spray management of set-aside was also much simpler than manipulating pesticides in crops. In temperate agricultural systems, in Europe or beyond, large-scale developments in pest control technology and machinery have created largescale changes in agricultural landscapes (O’Connor & Shrubb, 1986; Chamberlain et al., 2000; Donald et al., 2006). It is likely that larger expanses of crops extended uniformity, beyond the foraging range of many breeding bird species, which in the U.K. typically operate within 500 m radius of their nest site. In the U.K., according to government Public Service Agreement (P.S.A.), and Farmland Bird Indicator remains close to its lowest measured point (B.T.O., 2007). This is despite recent, laudable, developments for prescriptions within English agri-environment schemes and is due to crop commodity prices and farming convenience reducing the complexity of mixed rotations within say 1-km area (including the loss of non-cropped or fallow areas). With suitable planning at an appropriate scale, bird species can be responsive to newly available ‘habitats’ (including crops). However, most probably a much higher proportion of farmland then at present, must contribute, as both crops and as non-cropped habitats (fallows and stubbles). Benton et al., (2003) argue that policy frameworks need to recreate complexity as the key to restoring and sustaining biodiversity. Although every opportunity should be taken to reduce pesticide use in crops, for most farmers, rotation management is conceptually easier, with lower economic risk. The flexibility of farmers to choose the content of mixed rotations may be limited by market constraints but mixed rotations have a historical basis for aiding pest control, which may mean some agronomic justification is reclaimed through longer-term planning. At present localised success will depend on the individual mindset of farmers and their economic circumstances. In some parts of Europe, such as Norway, improved public attachment to their rural culture, landscape and general environment, is used to engagement people in rural issues, ultimately to pay more for associated products and lifestyles. Getting money into the system, to pay farmers properly for inconvenience will require stronger
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support from the public for what farming can be perceived to achieve and provide for them, apart from food – such as aesthetics and recreation. Improved public perceptions of farming would help this process, and help encourage farmers who have, in fact, worked hard, both past and present, to provided space and time for the environment and specifically for biodiversity. Acknowledgements Thank you to Unilever Research and Development for the “Colworth Farm Project”, and also Penny Hemphill, Tim Pankhurst, Paul Lee, the Suffolk Wildlife Trust & Simon Groves (ADAS), David Pendlington, Jos vanOostrum and Vanessa King. Special thanks to to Neal Ravenscroft. Colworth was funded by Unilever PLC and The European Regional Development Fund via the North Sea Interreg 111b programme. SAFFIE was sponsored by the Defra, the Scottish Executive Environment and Rural Affairs Department and Natural England via the Sustainable Arable LINK programme. Industrial funders were British Potato Council, Agricultural Industries Confederation, Crop Protection Association, Home-Grown Cereals Authority, Jonathan Tipples, Linking Environment And Farming (LEAF), Royal Society for the Protection of Birds, Sainsbury’s Supermarkets Ltd, Syngenta, the National Trust, and Wm Morrison Supermarkets PLC. Special thanks to Tony Morris (RSPB) and Rachel Coombes (B.T.O.). References Benton, T. G., Vickery, J. A. & Wilson, J. D. (2003). Farmland biodiversity: is habitat heterogeneity the key? Trends in Evolution and Ecology 18: 182– 188. Boatman, N. D., Brickle, N. W., Hart, J. D., Milsom, T. P., Morris, A. J., Murray, A. W. A., Murray, K. A. & Robertson, P. A. (2004). Evidence for the indirect effects of pesticides on farmland birds. Ibis 146: 131–143. Brickle, N. W. & Peach W. J. (2004). The breeding ecology of Reed Buntings Emberiza schoeniclus in farmland and wetland habitats in lowland England. Ibis 146: 69–77. Browne, S. J., Vickery, J. A. & Chamberlain, D. E. (2000). Densities and population estimates of breeding Skylarks Alauda arvensis in Britain in 1997. Bird Study 47: 52–65. B.T.O. (2007). British Trust for Ornithology web site. www.bto.org/research/ indicators. Buckingham, D. L., Evans, A. D., Morris, A. J., Orsman, C. J. & Yaxley, R. (1999). Use of set-aside in winter by declining farmland bird species in the UK. Bird Study 46: 157–169. 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. Chamberlain, D. E., Wilson, A. M., Browne, S. J. & Vickery, J. A. (1999). Effects of habitat type and management on the abundance of skylarks in the breeding season. J. Appl. Ecol. 36: 856–870. Curry, D., Browning, H., Davis, P., Ferguson, I., Hutton, D., Julius, D., Reynolds, F., Tinsley, M., Varney, D. & Wynne, G. (2002). Policy
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Commission on the Future of Farming and Food. Cabinet Office, London. Defra (2007). Department of Environment Fisheries and Food web site. www.statistics.defra.gov.uk. Donald, P. F. (2004). The Skylark. Poyser. Donald, P. D., Sanderson, F. J., Burfield, I. J. & van Bommel, F. P. J. (2006). Further evidence of continent-wide impacts of agricultural intensification on European farmland birds 1990–2000. Agriculture Ecosystems and Environment 116: 189–196. Evans, A. D. (1997). Seed-eaters, stubble fields and set-aside. Proceedings 1997 Brighton Crop Protection Conference, 907–922. British Crop Protection Council, Farnham. Field, R. H. & Anderson, G. Q. A. (2004). Habitat use by breeding Tree Sparrows Passer montanus. Ibis (Suppl. 2): 60–68. Gillings, S. & Fuller, R. J. (2001). Habitat selection by Skylarks Alauda arvensis wintering in Britian in 1997/98. Bird Study 49: 293–307. Gibbons, D., Avery, M., Baillie, S., Gregory, R., Kirby, K., Porter, R., Tucker, G. & Williams, G. (1996). Bird species of Conservation Concern in the United Kingdom, Channel Islands and the Isle of Man: revising the Red Data list. RSPB Conservation Review 10: 7–18. Green, R. E. (1984). The feeding ecology of partridge chicks (Alectoris rufa and Perdix perdix) on arable farmland in East Anglia. J Appl. Ecol. 21: 817–830. Hawthorne, A. & Hassall, M. (1995). The effect of cereal headland treatments on carabid communities. In: Toft, S. & Reidel, W. (eds.) Arthropod natural enemies in arable land I. Acta Jutlandica 70: 185–198. Henderson, I. G. Cooper, J., Fuller, R. J. & Vickery, J. (2000). The relative abundance of birds on set-aside and neighbouring fields in summer. J. Appl. Ecol. 37: 335–347. Holland, J. M., Hutchison, M. A. S., Smith, B. & Aebischer, N. J. (2006). A review of invertebrates and seed-bearing plants as food for farmland birds in Europe. Annals of Applied Biology 148 (1): 49–71. Marchant, J. H., Hudson, R., Carter, S. P. & Whittington, P. (1990). Population Trends in Breeding British Birds. British Trust for Ornithology, Tring. Morris A. J., Wilson, J. D., Whittingham, M. J. & Bradbury, R. B. (2005). Indirect effects of pesticides on breeding yellowhammers (Emberiza citrinella). Agriculture, Ecosystems and Environment, 106: 1–16. O’Connor, R. J. & Shrubb, M. (1986). Farming and Birds. Cambridge University Press, Cambridge. Potts, G. R. (1986). The Partridge. Collins. London. Raven, M. J. & Noble, D. G. (2006). The Breeding Bird Survey 2005. BTO Research Report 439. B.T.O., Thetford. SAS (2002). Statistical Analysis System: Version 9.1. SAS Institute, Cary, NC, USA. 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 Bird Census indices. J. Appl. Ecol. 35: 24–44.
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Sotherton, N. W. & Self, M. J. (2000). Changes in plant and arthropod diversity on lowland farmland: an overview. In: The Ecology and Conservation of Lowland Farmland Birds (Aebischer, N. J., Evans, A. D., Grice, P. V. & Vickery, J. A. (eds) British Ornithologists Union. Sheldon R. D, Chaney K. & Tyler G. (2002). Lapwings, earthworms and agriculture. Aspects of Applied Biology 67: 93–100. Stoate, C., Moreby, S. J., & Szczur, J. (1998). Breeding ecology of farmland yellowhammers Emberiza citrinella. Bird Study 45: 109–121. Unilever (2005). The Colworth Farm Project: Putting Sustainable Agriculture To The Test. Unilever, Sharnbook. 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. Cons. 119: 19–39. Wilson, P. J. (1992). Britain’s arable weeds. British Wildlife 3: 149–161. Wilson, J. D., Arroyo, B. E. & Clark, S. C. (1996). The diet of bird species of lowland farmland: a literature review. Unpublished report to the Department of the Environment and Joint Nature Conservation Committee. University of Oxford and Royal Society for the Protection of Birds, Sandy. Wilson, J. D., Evans, J., Browne, S. J. & King, J. R. (1997). Territory distribution and breeding success of skylarks Alauda arvensis on organic and intensive farmland in southern England. J. Appl. Ecol. 34: 1462–1478. Dr I. Henderson BTO The Nunnery Thetford Norfolk IP24 2PU
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