To define, objectively, a comprehensive set of functional groups of bird species in Scotland, taking into account season and spatial scale; to use these groups to assess how functional biodiversity of Scottish birds is related to land cover/use patterns.
Analyses were of all bird species (resident or migrant) present in Scotland, excluding only the rarest and seabirds which come ashore only to breed, at both individual territory (`Functional Groups')and landscape (`Landscape Clusters') scales, separately for summer and winter, using data covering the whole of Scotland. Functional Groups were defined by species' use of a large number of habitat features for feeding, nesting, roosting/perching and cover/shelter. Landscape Clusters were derived from the strength of species' associations with six land cover/use strata: arable (cropped land), inbye (controlled/managed grasslands), mooredge (mixed moorland/non-moorland landscape), moor (large areas of essentially uninterrupted moorland), plateau (areas containing the highest or most climatically severe moorland or montane land) and non-agricultural (principally urban areas, large forest blocks and large water bodies). Bird species and Functional Groups were related to landscape-scale land cover/use by their associations with strata. Biodiversity patterns in relation to land cover/use were similarly examined both as species diversity and Functional Group diversity.
Both Functional Groups and Landscape Clusters were clearly interpretable ecologically. Species within Functional Groups had consistent patterns of association with strata, linking birds with land cover/use at landscape as well as local habitat scale. However, Landscape Clusters showed several differences from Functional Groups, mainly linked with the relative importance of `local' and landscape-scale habitat features, or limited geographical range of some species. While there were clear groupings of species related to land cover/use in summer, bird distributions in winter were primarily related to climate severity, with broad land cover/use of only secondary importance.
Bird biodiversity varied functionally as well as numerically between strata. Variation between strata was consistent with the habitat-use characteristics of each Functional Group. Limited geographical range of some species reduced the per-square species richness of all Functional Groups below their potential maximum but the degree of reduction varied markedly between Functional Groups.
Structural heterogeneity in the landscape was an important determinant of bird biodiversity, with both homogeneous and heterogeneous landscape types (strata) of value to different Functional Groups. The importance of the lowland strata for birds generally, especially in winter, contrasted with the specific importance of every stratum for particular Functional Groups, especially in summer.
The combination of Functional Groups and land cover/use stratification enables a concise, comprehensive, direct assessment of bird biodiversity in relation to land cover/use at landscape scale. It also provides a framework within which effects of regional or global changes in environment or land use on bird biodiversity can be estimated. Total species richness in a stratum is a poor measure of its importance for overall bird biodiversity; species richness within Functional Groups, together with the analyses of Functional Groups in relation to the strata, provides a better base for the formulation of national-level conservation and biodiversity policy.