Meadow pipits, red grouse and the habitat characteristics of managed grouse moors.
The abundance of meadow pipits (Anthus pratensis) appears to be a good indicator of the breeding density of hen harriers (Circus cyaneus) on moorland managed for red grouse (Lagopus lagopus scoticus) in Scotland. High densities of hen harriers can limit grouse populations at low density and reduce shooting bags, with repercussions for grouse moor management and conservation. We therefore examined the habitat characteristics of managed grouse moors, asking whether changes in vegetation could alter the ratio of pipits, and thus harriers, to grouse. We examined grouse abundance and habitat on 69 sites of 1 km2 in upland UK, of which pipit abundance was studied on 36. Similar data were collected on 73 sites of 25 ha within the Langholm estate in south-west Scotland in May-July 1996, in order to make a within-estate and among-moor comparison. The distribution of pipit abundance on the Langholm estate was similar to that seen in the extensive among-moor study. Pipit and grouse abundance were related to habitat in similar ways in the two data sets. Pipits were the most frequent passerine, but their abundance was not related to grouse abundance. Pipit abundance declined with increasing muirburn (burnt Calluna stalks) and heather (Calluna vulgaris), but increased with grass cover. In a linear regression model Calluna, Sphagnum and muirburn cover accounted for 42% of the variation in pipit abundance across UK. Grouse abundance was influenced by the regional location of the grouse moor and to a lesser extent by its altitude. There were more grouse on English moors with less patchy habitats. Bird species declined with increasing Calluna and Sphagnum cover and habitat patchiness. Bird species diversity increased from west to east and on moors with more muirburn. This study provides evidence that meadow pipits are influenced by habitat characteristics on moorland managed for grouse. This work also illustrates how habitat management may be able to mitigate human-wildlife conflicts: long-term increases in heather cover and management of this habitat by muirburn on grouse moors may reduce pipit numbers and thus reduce the ratio of hen harriers to grouse. However, the effects of such vegetation change on other components of the upland bird assemblage requires further investigation.