Moorland birds and their predators in relation to afforestation
The breeding bird assemblages of blanket bog and moorland habitats in the United Kingdom are of special international importance. They are characterised by species drawn from arctic to temperate regions breeding at high density and showing a particular affinity for open, in parts waterlogged, grazed and burned landscapes. Much recent debate has focussed on the effects of conifer plantations on the distribution and breeding success of these birds. This study concentrates on differences in breeding distribution and success of selected moorland birds. On blanket bog in Caithness and on heather moorland in Grampian Region, moorland waders Charadrii and red grouse Lagopus lagopus scoticus were counted using three methods cross-checked against each other; a) transects using trained dogs, b) listening for calls at dawn and dusk, and c) daylight transects without dogs. Counts were done on afforested ground and adjacent 'edge' areas, and on open moorland far from trees. In Caithness, densities of moorland waders on afforested ground started to decline as soon as planting began, and none was found inside plantations > 7 years old. Red grouse densities on afforested ground in Caithness and in Grampian rose higher than on open moorland areas during the first five years after planting, before declining. It is suggested that red grouse will disappear from afforested ground in Caithness 8-9 years after planting, and in Grampian 11-12 years after. On areas adjoining plantation < 8 years old in Caithness, densities and breeding success of waders and red grouse did not differ significantly from those on open moorland areas far from trees. However, next to older trees the densities of some waders were lower, and breeding success of golden plover Plurialis apricaria and red grouse lower than on open moorland. In Grampian, densities of red grouse did not differ between the different types of area, but breeding success was significantly lower on edge areas than on open moorland. Lower densities and poorer breeding in the two species mentioned above coincided with older nearby trees and taller ground vegetation. However, within areas there were no significant relationships between density and distance from the forest edge for any species, and similarly for breeding success.