The effect of management for red grouse shooting on the population densityof breeding birds on heather-dominated moorland

1. Breeding birds, vegetation and moorland management were surveyed in 320 1-km squares on 122 estates in upland areas of eastern Scotland and norther n England where red grouse shooting is a widespread land use. We assessed w hether population densities of 11 species of breeding birds differed betwee n heather-dominated moorland managed for red grouse shooting and other moor land with similar vegetation. 2. We classified estates that had a full-time equivalent moorland gamekeepe r as grouse moors. The mean density of red grouse shot per year was four ti mes higher and the mean density of gamekeepers was three times higher on gr ouse moors than on other moors. Rotational burning of ground vegetation cov ered a 34% larger area on grouse moors than on other moors. 3. Selection of heather-dominated squares resulted in similar composition o f vegetation on grouse moors and other moors (about 76% heath, 12% grass, 8 % bog, 2% flush and < 1% bracken on both types). However, grouse moors tend ed to have less tall vegetation than other moors and differed significantly in some other characteristics of the vegetation, topography and soil type. 4. Densities of breeding golden plover and lapwing were five times higher a nd those of red grouse and curlew twice as high on grouse moors as on other moors, while meadow pipit, skylark, whinchat and carrion/hooded crow were 1.5, 2.3, 3.9 and 3.1 times less abundant, respectively, on grouse moors. T he differences in density between moorland types remained significant (P < 0.001) for golden plover and crow and approached significance (P < 0.10) fo r lapwing and meadow pipit after allowing for variation among regions. 5. We used Poisson regression models to relate bird density to vegetation c over, topography, climate and soil type. After adjusting for significant ef fects of these habitat variables, significant differences in bird density b etween the two moorland types remained for six species, although their magn itude was reduced. 6. Correlations of adjusted bird density with measures of different aspects of grouse moor management provided evidence of a possible positive influen ce of predator control(assessed using crow density) on red grouse, golden p lover and lapwing. The control of crows by gamekeepers is the most probable cause of the low densities of crows on grouse moors. There was evidence of a positive effect of heather burning on the density of red grouse and gold en plover and a negative effect on meadow pipit. Multiple Poisson regressio n indicated that predator control and heather burning had significant separ ate effects on red grouse density. Significant relationships between adjust ed breeding bird densities and the abundance of raptors and ravens were few and predominantly positive. 7. The results provide correlative evidence that moorland management benefi ts some breeding bird species and disbenefits others in ways that cannot re adily be explained as effects of differences in vegetation type or topograp hy. However, experimental manipulations of numbers of some predators and he ather burning are required to test these findings.