Impacts of predator abundance on red grouse Lagopus lagopus scotica during a period of experimental predator control.

Abstract

During a nine-year study manipulating predator abundances, post-breeding numbers of red grouse Lagopus lagopus scotica increased initially in response to experimentally reduced levels of key predator species (i.e. red fox Vulpes vulpes, carrion crow Corvus corone, stoat Mustela erminea and least weasel M. nivalis), but subsequently declined whilst predator control continued. Raptors, which were not controlled, were also present and may have influenced grouse demography. Our study examines the relative importance of controlled predators and raptors on grouse breeding success and survival. Raptor abundance did not differ between periods of predator control and periods of no predator control. However, during the breeding season, the survival of adult grouse was negatively correlated with the abundance of both raptors and controlled predators. Within the group of controlled predators, the strongest effects on red grouse adult survival were attributed to small mustelid abundance. Grouse breeding success was negatively correlated with the abundance of controlled predators, particularly carrion crows; however, no significant effect of raptor abundance was detected.