Post-Pleistocene differentiation is less marked in the penguins than in the petrels. Of 13 penguin species resident in this region, only the Macaroni (Royal) Penguin (Eudyptes chrysolophus ) has a well defined subspecies, schlegeli, which breeds at Macquarie Island. In contrast, subspeciation in the endemic South Pacific forms of the albatrosses (Diomedeidae) has been strong. Some full species are clearly masquerading as subspecies in the present taxonomy. Needing revision are: the Southern and Northern Royal Albatrosses (Diomedea epomophora); the New Zealand forms of the Wandering Albatross (D. exulans ); the two Black-browed Mollymawks (D. m. melanophris and D. m. impavida), the two colour morphs of the Buller's Mollymawk (D. bulled); and the three distinctive 'cauta' mollymawks, (D. c. cauta, c. salvini, and c. eremita). On the basis of morphology, behaviour, distribution and genetics, there is a good case for separating the mollymawks from the greater albatrosses at the genus level (i.e., retention of the name Thalassarche).

The smaller petrels of the region are mostly circumpolar in their distributions, although there are some geographical and behavioural differences because of the urge to return to their place of birth. Two sibling species of the Giant Petrel (Macronectes giganteus and M. halli) at Macquarie Island are reproductively isolated by a difference of some six weeks in their breeding schedules (Bourne and Warham, 1966). Unsuccessful interbreeding has been observed there by Johnstone (1977). Successful hybridization occurs at South Georgia, a fact attributed by Hunter (1983) to abundant local food supplies. This highlights the taxo-nomic difficulties that can arise with widely distributed species and demonstrates that birds of the same species living in different regions of the circumpolar ocean can adopt differing behaviours as a result of food abundance. Another behavioural difference occurs with the Snow Petrel (Pagodroma nivea) which is common in ice-free waters of the Scotia Sea (J.P. Croxall, pers. comm.); yet in the Pacific, the Snow Petrel rarely ventures far from the ice edge. Paucity of the region's food north of the ice edge may be a reason, but other factors might include flight distances to nest sites. The sea ice in this region from open water to Marie Byrd

Land on the Antarctic coast can be as much as 500-1,000 km — even in summer.

The increasing number of specimens of oceanic birds from their breeding localities in recent years has the potential to aid taxonomy greatly, and this information could be combined with modern biochemical techniques to unravel the complexities in several groups, such as the urinatrix subspecies of the Common Diving Petrel (Family Pelecanoididae). Much further work remains to be done.

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