Pied Currawongs and the decline of native birds

Predation pressure by Pied Currawongs, Strepera graculina, has been implicated as a principal factor in the decline of native bush bird populations. We review the available literature, analyse the types of avian species reported as being preyed on by currawongs, and examine whether this evidence suggests that increased currawong predation is limiting bird populations. Virtually all species reported as prey could be classified as 'introduced/common' and 'native/common'. The results suggest that predation is greatest on introduced/common species, and less than expected on native/common species and native/rare species. Currawongs seem to be generalist predators and do not appear to target any particular size or age range of avian prey. Nonetheless, it is not clear that currawongs are primarily responsible for predation on both nests and adults in all populations of small native birds, nor are the possible compensatory effects of density-dependent population growth rates in small Australian passerines well understood. It is also difficult to separate the effects of predation (increased mortality, possible reduced recruitment) from the effects of gross habitat change (degradation, fragmentation, changes in species composition and/or abundance). We discuss the limitations of some previous studies on currawong predation, and suggest possible directions for future research.