Birds of Upland Margins 2: Changes in populations of birds associated with grassland in the upland margins

by Ian Henderson

While attention is firmly focused on declining populations of birds on lowland farmland, evidence is gathering on the plight of foraging and nesting birds in pastoral upland areas. Here, some breeding waders (BTO News 247) and species of high conservation concern, such as Black Grouse, have received special attention. For passerines, such as Skylark, Meadow Pipit and Whinchat, their changing status in these remote locations is poorly understood. To investigate this, we looked back, once again, at the Common Birds Census (CBC). Several CBC plots, located within the marginal uplands of Britain, were monitored between 1960 and early 1980s. Re-visits to 13 of these sites situated in northern England, southern Scotland and Wales, in 1999 or 2000, allowed changes in bird populations to be assessed over the approximate 20-year intervening period. For a more complete account of the findings see Henderson et al. 2004 Bird Study 51:12-19.

In the study of several upland pastoral areas, there were major declines in a number of passerines, including Whinchat.

Downward trends for grassland birds

Evidence emerged of major declines in the breeding populations of those species most closely associated with grassland habitats (see Table 1). Among passerines, Skylark, Wheatear, Whinchat, Yellow Wagtail and Yellowhammer had each declined by over 80%. Redshank,
Yellow Wagtail, Dipper, Whinchat, Wheatear, Ring Ouzel and Yellowhammer were found on less than half the number of plots from which they were originally recorded, and only Curlew showed no change in status.

Apart from Dipper, most declining species were closely associated with open, grazed or unimproved grassland habitats for both breeding and foraging purposes.
The species that increased in abundance included Woodpigeon, Pied Wagtail, Carrion Crow, Jackdaw and Goldfinch, each having more generalist habitat requirements and with less dependence on grassland. Meanwhile, most woodland or woodland edge species, apart from Willow Warbler, showed no significant change in status.

Our data are consistent with both an intensive RSPB study reporting strong declines for Ring Ouzel, and a previously recorded decline of between 55% and 94% for Yellow Wagtails in the English Pennines. The upland breeding population of Yellow Wagtails in the UK is now almost certainly exceeded by lowland populations in crops.

Declines for Whinchat and Wheatear, for which marginal upland habitats probably hold a major proportion of the UK population, follow range contractions from historically occupied lowland habitats. Declines in two common and widespread species, Skylark and Meadow Pipit suggest that very large areas of upland breeding habitat may have become less suitable for nesting or foraging since the 1970s.

Explaining declines

Direct explanations for many of the declining trends reported above are not readily available but the broad composition of species affected suggests that changes have not been restricted to specific habitats. For example, Grey Partridge, Skylark, Whinchat and Yellowhammer prefer drier conditions to Redshank, Snipe, Yellow Wagtail and Reed Bunting. It was apparent that improved pastures had become more prominent on all surveyed sites since the 1970s, a trend that was consistent with conditions in the Yorkshire Dales National Park where improved pastures increased by 24% in the 10 years of the 1980s.

Elsewhere across Britain, widespread changes to the composition of upland habitats have resulted from increased grazing densities, particularly from sheep in areas of England and Wales, where their numbers at least doubled between 1980 and 1990. Changes in grazing and grassland improvement tend to reduce floristic variability and increase the occurrence of shorter and denser grass swards. This may increase predation risk, since birds nesting in more exposed, grazed swards, become more vulnerable to increasing numbers of predators such as crows and foxes, that track livestock. There is evidence, for example, that in Lapwing, clutches may suffer higher rates of predation in improved rather than unimproved grasslands.
The production of silage rather than hay intensifies the cutting regime of grassland, to which Yellow Wagtails are particularly sensitive. Remote areas have also become more accessible to modern machinery allowing many sensitive habitats to experience a rapid transformation in floral composition.

Future prospects?

Overall, the demographic mechanisms affecting bird populations in the uplands are poorly understood. Currently the conservation profile of upland farmland in the UK includes options within agri-environment schemes. However, the success of these prescriptions will be difficult to assess without data from representative monitoring studies.

Grazing and grassland improvement could lead to an increase in predation of some ground-nesting species such as Lapwing.

Acknowledgements

As always, thank you to all Regional Representatives, volunteer fieldworkers and landowners who made the study possible, and to JNCC, the funders of CBC.

The above article was first published in BTO News 254 (Sept-Oct 2004).

Back to Conservation Advice home