The Pied Currawong's role in avian nest predation: a predator removal experiment

Abstract

Pied Currawongs Strepera graculina have been implicated as a major threat to the persistence of small passerines in urban and rural landscapes through their intense nest predation while raising their young. Pied Currawongs have recently increased in abundance and colonized new areas, due to the planting of exotic berry-bearing trees and shrubs. In association with habitat fragmentation, this may have intensified their predatory impact. We measured the rate of predation on 416 artificial nests, using quail and plasticine eggs, in a 240 ha remnant of eucalypt woodland. Nests were placed in one grid from which Pied Currawongs were removed and in one control grid. The level of predation was monitored before and after Pied Currawong removal. Overall, nest predation was extremely high with 91 % of all nests preyed upon in seven days. Moreover, nest predation decreased significantly following Pied Currawong removal, thus identifying them as significant nest predators. However, imprint evidence from plasticine eggs and the remains of real eggs indicate that other animals, particularly other birds, are also important predators. If this high level of nest predation is reflected in real nests and occurs over a number of years, it may lead to low recruitment of open-nesting birds at this site. If it occurs regionally, it could contribute to long term declines of these species. Our findings suggest that even quite large woodland fragments may be too small to sustain many declining bird species.