Birds of upland margins 1: An overview

by Rob Fuller

The edges of our uplands are important places for birds. The BTO has been involved in several studies of these habitats in Scotland, Wales and England. The first of two articles on this subject draws on this work to discuss the bird communities of the upland margins and the changes that they face.

The uplands of Britain are extremely diverse in character and in the habitats they provide for birds. Many of us equate the uplands with birds such as Golden Plover, Red Grouse, Merlin and Golden Eagle — species that are typical of wild moorland and mountain landscapes. However, the edges of many of our upland tracts, where low-lying farmland gives way to relatively infertile moorland, hold bird communities very different to those of the upland interior. As one might expect, these bird communities are often intermediate in character between lowland and true upland. In conservation terms, the importance of the upland margins has become more widely appreciated in recent years. The mixture of habitats found in these areas often results in a fairly high diversity of species. Furthermore, several birds, such as Lapwing and Whinchat, have very large breeding populations in the upland margins. In some regions, several species nesting on open moorland, make heavy use of the margins for feeding, e.g. Twite, Golden Plover and Merlin.

The character of the upland margins varies greatly from one part of Britain to another and this strongly influences the nature of the bird communities. In the northern Pennines, numerous high-level grass fields are relatively rich in breeding waders. In some areas of Scotland there is considerable natural regeneration of trees and scrub on the lower moorland areas where grazing pressure by deer has been reduced; this generally results in an increase in bird diversity as described below. The situation in Wales is strikingly different to other parts of Britain. Here there is often a clearly defined zone of rough land between the farmland and the open hill. This land,the ffridd, is a highly variable mixture of bracken, rough grass, gorse, deciduous scrub and scattered trees; the bird communities are correspondingly diverse.

Declining bird populations

By comparison with the lowlands, population trends of many birds in the upland regions of Britain are poorly documented. However, two recent papers based on Common Birds Census (CBC) data, mainly for plots in the Pennines, indicate that major declines have occurred over the last 30 years in several species in the upland margins.

The first study was an analysis of trends on two CBC plots in the southern Pennines censused for many years by Eric Ward and David Hird (Fuller et al Bird Study 49: 146-152). In both cases there were large declines in Lapwing, Snipe, Skylark, Twite and Reed Bunting. The timing of the declines was different at the two sites, although Twite trends were almost identical (Figure 1). Numbers of most ground-nesting birds were much lower by the late 1990s compared with the 1970s although the number of species was similar. The population declines at one of the sites were probably linked with a switch from dairy to sheep farming as well as loss of rough grassland but changes in land-use were not obviously involved at the other site.

Fig. 1 Population trends on upland plots Population trends of four species on two upland CBC plots in the southern Pennines. The plots were 27km apart and were at similar altitude ranges (about 270-350 m). Densities (territories/km2) of four declining species are shown as running 3-year means. The black line shows the trend for a plot near Rossendale, Lancs, from 1968 to 1999. The red line shows the trend for a plot near Sutton-in-Craven, West/North Yorks, from 1972 to 1984 with the densitiy in 1999 shown as a cross. Twite were extinct on both plots in 1999

The second study, summarised in the following article, also recorded marked, long-term declines amongst grassland passerines and non-passerine species.
Whether bird populations have declined in other areas of marginal upland, where land-use patterns are often very different to those in the Pennines, is unknown. However, the BTO is undertaking work in Wales and Scotland that should help to understand better the habitat associations of birds in these areas and create a baseline against which future changes can be gauged.

Studies of upland margins in Wales and Scotland

Despite the uniqueness of the Welsh upland margins there has been remarkably little documentation of their bird communities. The BTO and RSPB have recently jointly analysed an extensive set of bird counts made in the mid 1980s at 120 ffridd sites spread throughout central Wales. There are major variations in the composition of the bird communities depending on whether the sites are bracken-dominated or grass-dominated and on the quantities of trees and scrub. Unlike the Pennine upland margins, the Welsh sites are relatively poor in breeding waders but often rich in scrub-nesting passerines. In the 1970s and ’80s some of the largest concentrations of breeding Whinchats in Britain occurred in these habitats. It would be valuable to repeat these surveys to assess the extent of population change in Whinchats and other upland edge species, especially since grazing pressure by sheep has been more intense in the Welsh uplands in recent decades than anywhere else in Britain. Also, little is known about the successional trends in the bird communities that would occur where the scrub was allowed to develop gradually into woodland.

In 1996 the BTO commenced studies of the effects on birds of birch and pine scrub development on moorland in eastern and central Scotland where grazing pressure by deer has been reduced. The aim of this work was to assess how the shift from open moorland through scrub to woodland would affect birds. Several long-term monitoring plots have beenestablished where bird populations can be measured in response to future habitat change.
So far we have detected very little change in either habitats or birds. The growth of trees is very slow in these northern sites and it will take many years before there are substantial changes in the bird communities.

Fig.2 Distribution of species across a successional habitat gradient Distribution of selected breeding species across a successional gradient from moorland, through birch scrub to old birch woodland at Dinnet National Nature Reserve, Grampian Region. Based on data collected in 1996. Dashed lines indicate lowest densities and thickest lines highest densities. Species codes: S Skylark, MP Meadow Pipit, CU Curlew, TP Tree Pipit, WW Willow Warbler, CH Chaffinch, WR Wren, R Robin, BT Blue Tit, TC Treecreeper, RT Redstart.

By comparing adjacent areas of moorland, open scrub, closed-canopy scrub and mature woodland it is possible to make predictions about long-term changes. Responses of several species to habitat change at Dinnet National Nature Reserve are summarised in Figure 2. With the colonisation of scrub there is a slight increase in numbers of species, although the bird community is a simple one, strongly dominated by three species: Willow Warbler, Chaffinch and Meadow Pipit. The richest habitats by far are old woodland which holds relatively high densities of cavity and crevice-nesting birds including tits, Treecreeper and Redstart. Interestingly, we have found that few species are confined to these northern scrub habitats — the mature woodland supports most of the species that can be found in scrub. In other words there appear to be rather few scrub specialists in the birch and pine scrub which contrasts with scrub habitats in southern Britain where several warblers and Nightingale strongly select scrub habitats. However, one bird in particular is likely to benefit from expansion of scrub in the Scottish Highlands* – the Black Grouse.

*For further information on bird communities in scrub in the Scottish Highlands see: Gillings et al. 1998. Ornis Fennica 75:27-37;. Fuller at al. 1999. Vogelwelt 120 (suppl) 53-62; Gillings & Fuller 1998 Scottish Birds 19: 231-238; Gillings et al. 2000. Scittish Forestry 54: 73-85.

Change in the upland margins

The edges of our uplands have probably been susceptible to change for hundreds of years, depending on the economics of farming and local population pressures. Grazing pressures and demand for land will have fluctuated over the years and the boundary between productive and abandoned land may have shifted back and forth. In recent times it seems likely that increased grazing pressure, scrub removal, bracken control, re-seeding and drainage will have affected the range of habitats available to birds in many areas.

Reed Bunting populations showed a marked decline on two Common Bird Census plots in the Pennines since the early 1970s.

There is evidence that intensification of grassland management in the Pennines has resulted in declines in ground-nesting birds. Elsewhere it is less clear whether recent changes in land-use have had more than local effects on bird populations. With changes in agricultural support, it is possible that in the coming decades we may see less intensive use of many marginal farming areas, especially reduction in sheep, where the soils are infertile and the terrain rugged. Provided that browsing pressure from deer is not too great we may see a gradual shift of many areas towards woodland. This is an especially exciting prospect in Scotland where there are opportunities for large areas of old growth woodland to become established through natural regeneration. However, a balance between open moorland, scrub and woodland is desirable to provide habitats for all species of birds and other wildlife. The BTO will be able to play a part in helping to identify what this ideal balance might be.

Acknowledgements

Many thanks to all those people who have helped collect the data for the studies outlined in this article. The Scottish scrub work has been co-ordinated by Simon Gillings with help from Dawn Balmer, Andy Wilson and Su Gough. The Welsh ffridd work is a combined effort by BTO and RSPB staffincluding Phil Atkinson, Greg Conway, Martin Garnett and Ian Johnstone. The late Colin Bibby was the instigator of work on the birds of ffridd in the 1980s. Much of the work outlined here was carried out under the BTO-JNCC partnership on behalf of English Nature, Countryside Council for Wales, Scottish Natural Heritage and the Environment & Heritage Service in Northern Ireland and was part funded from the legacy of Mrs Firth.

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

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