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Lowland Grassland Survey

This BTO-funded survey is designed to assess the generality of bird preferences for grassland types, in terms of sward composition and management. The project is linked to intensive MAFF-funded grassland research elsewhere within the UK.

Fieldwork involved two summer visits to 1-km squares. The survey, originally planned for summer 2001, took place in summer 2002 due to the Foot and Mouth crisis, although winter work was completed in 2000/2001.

Long-term declining bird species in grass-dominated landscapes have included Grey Partridge, Lapwing, Skylark and especially seed-eating finches and buntings not to mention Corncrake. Just as with arable farmland, lowland grasslands are subject to intensive management regimes that improve sward quality and quantity for livestock. Typical activities include reseeding, fertilizer applications, frequent cutting for hay or silage or high-density grazing itself, each of which can lead to simplified vegetation characteristics, reduced invertebrate populations and a predicted reduction in sward-suitability for foraging and nesting birds. Although some population changes of birds in grassland landscapes have been attributed to reduced habitat complexity between fields, within-field sward composition is also likely to be an essential factor in determining the way birds use grassland. The visual characteristics of grassland, however, are far less distinctive than those that exist between different arable crops so that broad relationships between birds and sward condition are difficult to identify and categorize.

The lowland grassland survey collected data from summer (2002) and winter (2001/2002) from 94 farms in England, southern Scotland and Wales. Our analysis found that higher densities of “worm-eating” bird species, such as thrushes and crows, on grassland with a short, dense uniform sward, typically characteristic of improved grassland. In contrast, surface-feeding species, including Robin and Dunnock, occurred at highest densities on uneven, tussocky swards that are characteristic of less improved grassland. It is likely that in the former species, those such as Blackbird prefer good access to soil organisms in the way that thrushes commonly forage on playing fields. The surface-feeding species, however, are more likely to respond to the higher densities of invertebrates that live in structured swards above ground.

Also see BTO News number 247.

For further details of this survey please contact at BTO, Thetford.