Sunday, 26 February 2017

The Yellow-crested or Lesser Sulphur-crested Cockatoo. Part 4. Geographical Origins of the Feral Population in Hong Kong

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

Can we deduce where the feral population of Yellow-crested Cockatoos in Hong Kong originated?

As I explained in Part 2 of this series, there are seven currently recognised subspecies of Cacatua sulphurea but since some of them are from small or relatively remote island groups which might not have been the easiest places to collect from I would argue we can narrow the possibles to four, viz:

C .s .sulphurea (Gmelin,1788) from Sulawesi
C .s. occidentalis Hartert 1898. Lesser Sunda islands from Lombok to Alor
C. s. parvula (Bonaparte, 1850. Timor
C .s. citrinocristata (Fraser, 1844). Sumba

Collar & Marsden (2014) have done a great job in both pulling together what is known on the subspecies and in making a statistical analysis of morphological characters. However, for my purposes I am relying on differences in the colour of the crest and on the depth and size of the patch of colour of the ear-coverts.

I do not know and do not know if anybody knows the genetics of these differences. Hybrids between Yellow-crested (of unstated lineage) and Citron-crested have been bred. I have found one photograph of such a bird which suggests that the colour of the crest tends towards yellow but have found no indication of what happens in later generations. However, it could be argued that if a citron-crested individual has been spotted in the past few decades amongst the feral birds of Hong Kong, then it is likely that citrinocristata has contributed genes.

In photographs of cockatoos in Hong Kong available on the internet and in photographs (taken in 2003-8) shown in A Photographic Guide to the Birds of Hong Kong, the occasional bird with an orange crest can be seen. Viney, Phillipps & Ying’s The Birds of Hong Kong and South China (8th edition, 2005) states that citrinocristata is present. However, the literature is confused: this source says citrinocristata was not introduced to Hong Kong. In passing it is worth mentioning that the IUCN Red List shows the species as a whole as having been introduced in Singapore with no mention of Hong Kong!

The Citron-crested is easy but what of the Yellow-crested? Viney, Phillipps & Ying (2005) state: Two races occur in HK: sulphurea [C. s. sulphurea] (yellow crest) and citronocristata… However, I am by no means sure that this is the case since none  of the birds we have seen, nor do any of the photographs I have been able to find, show the large deeper yellow ear-covert patch which appears characteristic of sulphurea. (There is also a stock photograph on Alamy which shows the deeper yellow patches of a bird photographed on Sulawesi.)

If we eliminate sulphurea as a major contributor to the present gene pool, that leaves occidentalis and parvula (once, remember, considered one and the same). The ear-covert patch of all the birds we saw in bird shops in the 1960s was relatively pale and the photographs of the feral birds show pale yellow patches. However, the patches do not seem sufficiently small to be parvula.

The photograph below is a greatly enlarged portion of a transparency of the female cockatoo we bought in Hong Kong. She was typical of all those we saw for sale then. Comparing the photographs of skins and the descriptions in Collar & Marsden (2014) leads me to suggest that the commonest form of the Yellow-crested cockatoo in the Hong Kong feral flock is occidentalis.

A greatly enlarged photograph of our female cockatoo in
Hong Kong in 1966 showing the pale yellow ear-covert patch

In terms of logistics in the 1960s and 70s, it could well have been easier to trap and transport cockatoos from Lombok (where they are no longer exist) and the chain of the Lesser Sundas extending east, including Sumba, to Jakarta or even Denpasar Airport (domestic flights in the 1960s) on Bali than to carry them on a fairly long sea passage from Sulawesi.

Determining from which island groups the Hong Kong flock is derived is not just of historic interest. Those conservationists considering reintroduction prefer to introduce the same subspecies as existed originally in the location. One those grounds they might reject the Hong Kong feral birds as a source (as suggested by Gibson & Yong, 2016). However, if they were the only source or if captive-bred birds of mixed origin were the only ones available, then I would be the first to say, introduce them and then let natural selection take its course (the outcome of which would be interesting). Better, surely, to have cockatoos of the same species on an island where they once existed than none at all.

Reflecting the birds being imported over the years, other species of cockatoo have escaped or been released, the commonest being the Tanimbar Corella (Cacatua goffiniana) which is hardly surprising given the numbers being traded in the 1970s. We saw a few Salmon-crested (Moluccan) Cockatoos (C. moluccensis) and White Cockatoos (C. alba) in the bird shops in the 1960s and the odd one has turned up in the wild. The Hong Kong Bird Watching Society also lists the Palm Cockatoo (Probosciger aterrimus) as an escapee.

The status of introduced cockatoos in Singapore in shown here, and in Taiwan by Lin & Lee (2006).

Collar NJ, Marsden SJ. 2014. The subspecies of Yellow-crested Cockatoo Cacatua sulphurea. Forktail 30, 23-27.

Gibson L, Yong DL. 2016. Saving two birds with one stone: solving the quandary of introduced, threatened species. Frontiers in Ecology and the Environment. DOI: 10.1002/fee.1449

Hong Kong Bird Watching Society. 2010. A Photographic Guide to the Birds of Hong Kong (revised edition). Hong Kog: Wan Li Book Co.

Lin RS, Lee P-F. 2006. Status of feral populations of exotic cockatoos (Genus Cacatua) in Taiwan. Taiwania 51, 188-194.

Viney C, Phillipps K, Ying LC. 2005. The Birds of Hong Kong and South China (8th edition). Hong Kong Government.