Two New Petrels For One Old

Abstract from Ibis
2nd September 1996

Many birds exhibit different colour morphs while being considered the same species. There are, for instance, light and dark (and intermediate) Arctic Skuas breeding happily together - and having their genetics studied - in Shetland and other parts of the arctic.

Many of the specialist seabirds, the petrels, show these different colour morphs but conventional taxonomists classify them as the same species. Their measurements and structures are very much the same and they breed on remote islands where it is very difficult to determine whether their breeding habits are subtly different. As birds which have to live in the marine ecosystem it is not surprising that they should be very similar even if they have been separated for millions of years.

Mike Brooke and Graham Rowe began to wonder whether the dark morph of the pan-Pacific Herald Petrel Pterodroma heraldica which is particularly common on Henderson Island in the Pitcairn Group might be different. They seemed to breed apart, to have different calls, at slightly different times of the year and on different parts of the island. Now DNA sampling has proved them right and it is clear that there are two species on Henderson. The new one is dark morph, called the Henderson Petrel Pterodroma atrata, named in the latest issue of Ibis (138, 420-432).

Modern technology is also able to provide an estimate of how long the species have been separated and their estimate is about two million years. The picture is by no means clear as there are other populations of similar species that need investigation. Very sadly there are not as many as there should be since several forms have been rendered extinct in the last 300 years by Man - and his cats and rats.