The pied currawong's impact on smaller birds that are vulnerable to nest predation is controversial: several studies have suggested that the species has become a serious problem, but the truth of this widely held perception was queried in a 2001 review of the published literature on their foraging habits by Bayly and Blumstein of Macquarie University, who observed that common introduced birds were more affected than native birds. However, predation by pied currawongs has been a factor in the decline of Gould's petrel at a colony on Cabbage Tree Island, near Port Stephens in New South Wales; currawongs have been reported preying on adult seabirds. Their removal from the islands halted a decline of the threatened petrels. Furthermore, a University of New England study published in 2006 reported that the breeding success rates for the eastern yellow robin ("Eopsaltria australis") and scarlet robin ("Petroica boodang") on the New England Tablelands were improved after nests were protected and currawongs culled, and some yellow robins even re-colonised an area where they had become locally extinct. The presence of pied currawongs in Sydney gardens is negatively correlated with the presence of silvereyes ("Zosterops lateralis").