Pomatorhorine Relatives

Bird On! Abstract
12th May 1997

Older bird watchers would not be phased by this extraordinary name. It used to be used for the species now known as the Pomarine Skua. This is one of the Northern Hemisphere skuas and the second biggest. Recent research reported in the Proceedings of the Royal Society, 264: 181-190 by a team headed by Bernard Cohen of Glasgow University confirms what many people have thought.

This species is much more closely related to the Great Skua than the two smaller species (Arctic and Long-tailed). Indeed the two bigger species are more closely related to the Antarctic members of the family. This is confirmed by all sorts of means including DNA and studies of the species specific lice on the birds.

These are birds obviously related to gulls which mostly find their food by stealing it off other seabirds. The real question is what happened to the ancestral skuas to make the present relationships possible. There seem to be three scenarios according to Bernard and his co-authors:

1. The ancestral skua was originally Pomarine-like and the others arose from it.
2. This is a case of convergent evolution with the Pomarine evolving small skua characteristics anew.
3. The original Pomarine species arose through hybridisation

With a family of birds that seems to have arisen in the Southern Oceans and to have invaded the North, successfully, at least twice there would seem to be many other possibilities. Will we ever know? I expect so as our analytical techniques on DNA become better.

Chris Mead