MAGPIE PICA-PICA PREDATION ON BLACKBIRD TURDUS-MERULA NESTS IN URBAN AREAS

Estimates of rates of Magpie predation on Blackbird nests were made using plasticine eggs added to active clutches. Breeding densities of Blackbirds were lower than those recorded at other urban sites while Magpie densities were higher than those previously recorded in urban areas. Fewer than 5% of Blackbird nests produced flegded young. Predation caused most of the failures where a cause was known, though most nests failed for unknown reasons. Of identified predation, the majority was attributable to Magpies. The characteristics of predation where nest contents were removed suggest that these can probably also be attributed to Magpies. Given their high densities in urban areas and a lack of evidence of other predators, Magpies appear to provide the main predation pressure on Blackbird nests. At such low nesting success rates, the results from the present study suggest that Blackbird populations in urban parkland would be unlikely to maintain themselves. In this study, the breeding populations of Blackbirds were probably sustained by immigration from other habitats.