Associations between gamebird releases and generalist predators.
Abstract
The release of more than 40 million captive-bred pheasants and red-legged partridges in Britain annually represents a significant addition to the potential food resource base for predators and scavengers. If this extra food availability subsidizes predator populations, gamebird releases could increase predation pressure on other wild birds, affecting their populations. Using three extensive datasets, we examined the spatial relationships between reared and free-roaming gamebirds (pheasant Phasianus colchicus and red-legged partridge Alectoris rufa), and explored spatial and temporal associations between these gamebirds and five species of avian predator (buzzard Buteo buteo, jay Garrulus glandarius, raven Corvus corax, magpie Pica pica and hooded Corvus cornix and carrion Corvus corone crows combined) in lowland rural Britain. Patterns of spatial variation in the abundance of free-roaming gamebirds across Britain appear to be largely determined by gamebird releases, over and above any effects of land use or habitat. Predominantly positive associations between gamebird abundance (both reared and free-roaming) and the abundance and inter-annual population growth rates of predators tested suggest that large-scale variation in avian predator populations may be positively affected by gamebird releases. Synthesis and applications: The positive associations between large-scale gamebird release and predator populations shown here may have implications for prey populations if the releases cause increased predation pressure. If this occurs, game management could have an indirect negative impact on some prey species partially counteracting previously reported positive or benign effects of game management on wider biodiversity. Overall impacts of gamebird releases are likely to be determined by complex interactions between multiple factors, including induced predation pressure, better understanding of which would be possible with compulsory recording of releases and numbers of predators killed. Restriction of releases warrants further investigation and consideration as a potential conservation tool for wild bird populations.