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Modified management of agricultural grassland to promote in-field structural heterogeneity, invertebrates and bird populations in pastoral landscapes - BD1454

Modern pastoral farming methods are characterised by frequent and complete defoliations (through grazing or mowing) of dense, uniform swards dominated by palatable grasses and lacking botanical and structural diversity. Frequent and complete defoliations of grass swards prevent the completion of invertebrate life cycles and the seeding of grasses, thus removing key food resources for many farmland birds. Moreover, dense grass swards may render the invertebrates and seeds that remain in agricultural grassland inaccessible to birds. This loss of available food has probably been a major cause of the large population declines and the low densities of many priority farmland birds in grass-dominated regions of the UK. Several bird species that nest in grass suffer high rates of mortality due to mowing operations.

We propose three replicated field experiments, two that aim to promote invertebrate densities through relaxation of grazing, and one that aims to promote breeding success of birds through modified mowing. The grazing experiments involve the early cessation of summer grazing on intensive and semi-improved grassland with the aim of promoting densities of invertebrates that require grass foliage to remain in situ during late summer, winter or early spring to complete their life cycles. Spring and summer grazing treatments then aim to provide the preferred sward requirements of different farmland bird guilds. Both experiments aim to promote sward heterogeneity (and thereby bird access) and invertebrate abundance, and both will provide enhanced late-summer nesting opportunities and overwinter food resources for seed-eating birds. The third experiment aims to reduce the high rates of nest destruction experienced by the 31% of English and Welsh skylarks that nest in grass silage fields. Raised grass cutting heights followed by modifed methods of grass collection have the potential to raise skylark productivity to levels needed for self-sustaining populations, and at modest agronomic cost.

A key feature of our approach will be to establish experimental study plots in localities known to support breeding populations of priority farmland birds (e.g. buntings, finches, larks, thrushes) that are dependent on grassland as a foraging and/or nesting habitat. The findings of the experimental studies will be combined with those of a recent RSPB/EN study investigating the influence of grassland management on the breeding performance of yellowhammers in two pastoral regions of Britain. This latter study is nearing completion and is allowing us to investigate the effects of grassland management intensity on the abundance and availability of invertebrates, and consequent impacts on yellowhammer diet and breeding performance.

Each of our proposed experiments are based on a strong empirical understanding of the factors currently limiting invertebrate densities and skylark nesting success on agricultural grassland. The proposed treatments have a high probability of delivering biologically significant increases in invertebrate densities and nesting success, with potentially modest impacts on agronomic yield. Taken together, these studies will provide the basis for detailed management recommendations for possible inclusion as future ELS or HLS measures. This consortium has a proven track record of conducting rigorous and relevant experimental research on pastoral farmland, including a series of successful studies on declining farmland birds.

Project Documents
• Final Report : Modified management of agricultural grassland to promote in-field structural heterogeneity, invertebrates and bird populations in pastoral landscapes.   (2744k)
• Final Report - Annex : Appendices A-G.doc   (654k)
• Final Report - Annex : Appendices H-J.   (2753k)
• Final Report - Annex : Appendices K-M.   (362k)
• Final Report - Annex : Appendices N-T.   (496k)
Time-Scale and Cost
From: 2005

To: 2009

Cost: £799,882
Contractor / Funded Organisations
Royal Society for Protection of Birds, ADAS UK Ltd., CABI Bioscience
Agricultural Land              
Environmental Protection