A new shearwater on the Chathams

Forest and Bird, Volume 22, Issue 3, 1 August 1991, Page 6

A new shearwater on the Chathams

Alan Tennyson

I’ JANUARY 1990, Department of Conservation workers, Ron Nilsson and Jill West, were mystified by an unusual looking seabird which they caught at night on South East Island in the Chatham group. The bird was similar to a muttonbird or sooty shearwater, but instead of being dark below like a normal muttonbird, it was white underneath. On closer examination they noted other differences — its tail was longer and it was much lighter in weight. Not wanting to harm the emaciated bird, they released it, after taking measurements and recording plumage details. They concluded that it was either a very peculiar and partly albinistic sooty shearwater or a species previously unknown to science. Unfortunately, it was later found dead. The bird was sent to the National Museum in Wellington, where its skin and skeleton were preserved. Various seabird authorities examined the specimen and after debate decided that the bird was almost certainly a new species of shearwater. Not only were its plumage and measurements unique, but its skeleton was also quite distinct. These days it is very unusual to discover a new species of bird. However, scientists are fairly confident the Chatham bird is distinct because amongst shearwaters, there are no records of different species hybridising and there is little variation amongst individuals in populations. I was a member of a DoC expedition studying petrels on South East Island this

January. We searched for more of the unusual shearwaters but did not see any. If further birds are found, the species’ identity will be more certain and a conservation strategy can be formed. The story of the new shearwater may parallel that of the endangered Chatham Island taiko, which was rediscovered by David Crockett and his team in 1973. The taiko survived, unseen by researchers, for more than 100 years after being first scientifically described in 1867. Petrels and

shearwaters come ashore only at night and breed in long burrows. Therefore they can easily go unnoticed. It appears that the new shearwater has been overlooked until now. The discovery highlights again the unique nature of the animals and plants that have evolved on the Chatham Islands. Only time will tell what the future holds for the new shearwater, but let's hope that some more are found soon. x&