Associations between gamebird releases and general predators
Author(s): Pringle, H., Wilson, M., Calladine, J. & Siriwardena, G.M.
Published: July 2019 Pages: 12pp
Journal: Journal of Applied Ecology
Digital Identifier No. (DOI): 10.1111/1365-2664.13451
New BTO research has revealed that the release of Pheasants and Red-legged Partridges for commercial shoots may be boosting numbers of the avian predators and scavengers.
Every year, 41-50 million non-native gamebirds (Pheasant and Red-legged Partridge) are released in the UK. Fewer than half these birds are shot, meaning there is potentially a large food resource available to predators and scavengers, sustaining their populations above the levels they would otherwise reach. If it occurs, this inflation of predator numbers might alter predator-prey dynamics, increasing predation pressure on some vulnerable species, including declining breeding waders like Curlew.
This study used data from the Breeding Bird Survey and Bird Atlas 2007-11 to identify associations between the occurrence patterns of gamebirds and the abundance and population growth rates of several generalist predators, including Buzzard, Jay, Raven, Magpie and crows (Carrion and Hooded combined). While many other factors influence predator abundance, such as fine-scale habitat variation, availability of other food sources, and game management activities, the results suggest that large-scale variation in avian predator populations is predominantly positively affected by gamebird releases. The potential implications of this finding need to be thoroughly tested. Such tests could include regulation of releases on a trial basis, to determine effects on ground nesting birds, for example. The compulsory recording of releases and the number of predators controlled would also be valuable for a better understanding of the impacts, positive or negative, of gamebird releases on the wider environment.
1. 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 subsidises predator populations, gamebird releases could increase predation pressure on other wild birds, affecting their populations.
2. 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.
3. 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.
4. Synthesis and applications. The positive associations between large-scale gamebird release and predator populations shown here may have implications for prey populations that contrast with previously reported findings of positive 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.
This work would not have been possible without the vast amounts of data collected by volunteers.
This work was funded by Mark Constantine.
What effect might annual releases of non-native gamebirds be having on native biodiversity?
Henrietta Pringle reveals the work behind a recent paper on gamebirds and predation