A paper recently published in the OBC journal Forktail looks again at variability across populations of the Critically Endangered Yellow-crested Cockatoo Cacatua sulphurea of Indonesia and East Timor. Our aim was to identify characteristics of the different subspecies which can help captive breeders maintain genetic integrity of breeding stock and to help authorities to identify the origin of smuggled birds.
Modern taxonomic treatments recognise four subspecies of the cockatoo: sulphurea from Sulawesi and associated islands, abbotti on Masalembu Besar, parvula from Lombok to Timor, and citrinocristata on Sumba. All of these subspecies are extremely rare – abbotti numbers just a handful on a tiny island in the Java Sea. Perhaps the strongest population is of the distinctive citron-crested population on Sumba (one of the foci of Stu's own PhD many years ago).
|Cacatua sulphurea parvula on Komodo island, Indonesia (Photo: James Eaton/Birdtour Asia)|
We compared morphometric data (lengths of upper mandible, wing, tail and crest; colour and size of ear-covert patch) from 136 sexed museum specimens from across the range of the species. Specimens were examined, mainly by Nigel, at American Museum of Natural History, Natural History Museum, Tring, UK, Naturalis at Leiden, Staatliches Museum für Tierkunde, Dresden, National Museum of Natural History, Washington DC, USA (USNM); Zoologisches Museum, Berlin, and Academy of Natural Sciences of Philadelphia.
|Specimens (all female except that from Sumba, for which sex unknown) representing five taxa of Cacatua sulphurea, left to right: citrinocristata; parvula; occidentalis; djampeana; and sulphurea (Photo: Nigel Collar)|
There were clear differences among subspecies and also between the sexes in wing, tail and bill lengths. Ear covert patch size also differed. The races abbotti and citrinocristata were particularly distinctive and would be easy to identify in captivity. Biometric differences were quite complex: wing length differed across both taxon and sex; tail length differed across taxon but not sex; and the main differences in mandible size were across sex rather than taxon (with the otherwise ‘average’ sulphurea having a particularly large bill). Analysis of body structure also revealed important differences – with abbotti, parvula and citrinocristata having long wings and short tails, and the other species having short wings and long tails. There were also differences in ear-covert colour and size.
|The distinctive citrinocristata race from Sumba island, Indonesia (Photo: James Eaton/Birdtour Asia)|
|Males of three geographically adjacent taxa of Cacatua sulphurea: top C. s. sulphurea; middle C. s. djampeana; bottom C. s. paulandrewi type specimen (Photo: Nigel Collar)|
Under the taxonomic scoring system Nigel helped develop, the distinctive race citrinocristata from Sumba comes very close to species status, but not quite. Further evidence on behaviour and juvenile colouration may clinch this in the future.
|Distribution of the subspecies of Yellow-crested Cockatoo Cacatua sulphurea in Wallacea and adjacent islands. Included is the new taxon, paulandrewsi on the Tukangbesi Islands.|
There may be uncertainty about the specific status of citrinocristata, but there is little doubt that the species as a whole is in serious trouble right across its range. There are recent reports of declines on Komodo, a once large and well-protected population, while the Sumba population apparently remains low despite years of protection. We have a new project to resurvey populations of citrinocristata on Sumba and the species on Komodo. More on this project soon.