Aspects of red grouse Lagopus lagopus scoticus population dynamics at a landscape scale in northern England and the implications for grouse moor management

Abstract

Red grouse Lagopus lagopus scoticus are an important game species in the United Kingdom, with many areas of heather moorland managed specifically to produce them for driven shooting. In order to effectively manage red grouse populations it is important to have an understanding of their population dynamics and to determine which of the vital rates most effect population growth and recovery and whether these parameters can be influenced by management activities. The focus of my research was to provide a greater understanding of the respective roles of juvenile dispersal, heather management and mortality causes in red grouse population dynamics at a landscape scale in northern England. The study was undertaken between 1999 and 2005 and encompassed four privately owned grouse moors, covering some 113 km(^2) of heather dominated moorland. Central to my research was the ability to accurately and efficiently survey the distribution and abundance of red grouse across the study area. To facilitate this I evaluated a distance sampling method to survey red grouse across the study area pre-breeding in spring and post-breeding in summer. The distance sampling technique proved a reliable, repeatable and practical method for extensive surveys of red grouse. Grouse distribution data were used to construct spatial patterns of grouse abundance at a moor scale using a geostatistical interpolation technique. Rotational heather burning is practised by grouse moor managers to create a mosaic of heather ages which provide food, shelter and nesting habitats for red grouse. To assess the spatial and temporal effects of heather burning on grouse, I used an earth observation technique, using satellite remote sensing to map the habitat mosaic across all four study moors in 2000. Temporal effects of heather burning, from 2000 to 2005 were studied on one moor, with annual heather burning mapped annually. Dispersal is an important element of population dynamics which influences population growth and spread, gene flow and disease transmission. I used radio telemetry to investigate the timing, frequency and distances of dispersal in juvenile red grouse. Dispersal distance differed between sexes, with juvenile females dispersing on average 861 m (±120 SE) compared to 343 m (±31 SE) recorded in males. Population growth did not appear to be limited by dispersal and abundance increased until the density dependent effect of the parasitic nematode worm Trichostrongyle tenuis caused a population crash. On the study moors, grouse moor management resulted in rapid population growth with population oscillations caused by density dependent strongylosis induced crashes. The main cause of mortality was found to be shooting and to dampen population oscillations, modified shooting programmes to limit population growth in conjunction with parasite control measures should be adopted to better manage grouse populations.