The Yellow-crested or Lesser Sulphur-crested Cockatoo. Part 5. Do the feral cockatoos in Hong Kong damage the environment?

This is the 5th of a series of articles on this once common but now critically-endangered species from the islands of Indonesia and of Timor Leste.

Introduced species cause immense damage in many parts of the world. But what about the feral cockatoos in Hong Kong?

Part of the two pages on the feral cockatoos in
A Photographic Guide to the Birds of Hong Kong

In a review of invasive birds in Hong Kong in relation to the clearance of the natural tropical evergreen forest before the 18th Century and the progressive restoration of the forests, Michael Leven and Richard Corlett (writing in 2004) considered the topic:

Of the species that have invaded Hong Kong in historical times, both Yellow-crested Cockatoos and Rose-ringed Parakeets cause temporary damage to trees in city parks by feeding on growing shoots (Herklots 1967 [reference only to parakeets]. The Yellow-crested Cockatoo also causes similar damage to native trees in secondary forest on Hong Kong Island and occasionally destroys crops of unripe fruits (T Corlett pers. obs.). These birds are not abundant enough for these impacts to be serious, but any future increase in parrot populations should be viewed with some concern. Perhaps more significantly, it has been suggested that these species may have been implicated in the disappearance of the native Great Barbet Megalaima virens from Hong Kong Island, presumably by competition for nesting holes (Carey et al. 2001). This can be excluded as an explanation in the case of Yellow-crested Cockatoo, as Great Barbets vanished from Hong Kong Island prior to the occurrence of the cockatoos, but the disappearance of the barbets did coincide with the period of peak abundance of the parakeets.

So the answer seems to be that their effect is negligible

Leven MR, Corlett RT. 2004. Invasive birds in Hong Kong, China. Ornithological Science 3, 43-55