Woodland provides an important multi-taxa refuge within managed agricultural ecosystems, and historically was the predominant habitat in Britain. However, it exists today in fragmented patches, arguably conserved in part due to game shooting interests. Annually, more than 37 million omnivorous non-native common pheasants (Phasianus colchicus) are introduced into woodland to top up wild populations for the shooting industry yet the trophic impacts of these mass releases are not well understood. This thesis is the first study to assess quantitatively the impact of releasing pheasants on invertebrate communities. The data show that ground-active invertebrate biomass was lower in woodlands where pheasants are released, particularly in late spring. Also, the proportion of arthropod content in pheasant faecal samples was higher April to July, which suggests pheasants have an increased reliability on invertebrates after the shooting season ceases. Supplementary grain provided by gamekeepers during the release and shooting season may help mitigate pheasant predation pressure on invertebrate populations. Weak evidence was found that pheasant density affected biomass of Lepidoptera and Symphyta caterpillars along woodland tracks. Biomass was best predicted by plant species richness and temperature when using an information theoretic approach. There was no evidence to suggest that pheasants were avoiding aposematic larval morphotypes. Additionally, there was no impact of releasing pheasants detected in day-flying woodland Lepidoptera recorded in the Butterfly Monitoring Scheme, suggesting that any positive or negative effects of pheasant management on Lepidoptera are insubstantial. Overall, impacts observed in invertebrate populations could be driving trophic perturbations in woodlands. Mass-releasing non-native pheasants into already sensitive woodland ecosystems require further study to determine the implications for communities.
|Date of Award||2009|
|Supervisor||Stephen Harris (Supervisor) & Jane Memmott (Supervisor)|