Unintended consequences: how human intervention affects the ecology of urban birds

Urbanisation is an ever-growing threat to global wildlife. Nevertheless, urban areas around the world hold significant wild bird populations and urban birds provide a key connection between people and wildlife. Many people provide supplementary resources, such as food and nesting sites. However, even apparently beneficial actions may have unintended negative consequences. This work explores some of these direct and indirect effects. Grey Squirrels Sciurus carolinensis are a widespread, introduced species in the UK, acting both as a competitor for resources with birds and predator of their nests. When present, Grey Squirrels effectively excluded birds from supplementary feeding stations. Allowing them unrestricted access both supports their energy requirements and reduces its availability to target taxa, through both behavioural exclusion and food consumption. In addition, nest predation was higher in artificial nests adjacent to filled bird feeders which were frequented by potential nest predators and the exclusion of these predators did not significantly reduce nest predation. Providing point attractants during the breeding season may therefore depress local urban bird breeding success in addition to directly supporting predator/competitor populations. Garden supplementary feeding stations may also represent a threat to wild bird and human health through pathogen transmission. Bacterial communities were found to differ between two bird feeder types but there was little association between feeder usage by animals and bacterial load or pathogen presence in a typical UK suburban garden bird-feeding setting. Nest boxes are commonly provided for cavity nesting urban birds as an additional supplementary resource. Nest box using Blue Tits Cyanistes caeruleus and Great Tits Parus major differed in their use of anthropogenic material. Anthropogenic nest material was associated with lower arthropod diversity and ectoparasite predator abundance but higher ectoparasite loads. Higher arthropod diversity was linked to lower flea numbers, implying more complex arthropod communities depressed ectoparasite abundance though no direct link was found between these factors with breeding success. Domestic cats Felis catus are the most abundant predator in many urban ecosystems. Cat home ranges varied with level of urbanisation and they ranged significantly further during the night. To reduce the probability of Domestic Cats entering local protected areas a management zone of 300-400m from the nearest housing was estimated to be of management value and must be adjusted to the local landscape to ensure effectiveness. Despite the various negative effects highlighted in this thesis, the findings suggest that many of them can be mitigated, to ensure that our best intentions do effectively benefit urban birds