HUTTON — ON THE BIRDS OF THE SOUTHERN OCEAN. 237 



/«jw^»^^n«»(Temm.),andPe^»M5o5sc?« , ws{Gmel.),toP^»<sas«w«j7w 

 (Gould) ; and the Stormy Petrels of the northern seas, with the excep- 

 tion of Thalassidroma Leachii (Temm.), differ from those of the southern 

 seas only in some minor points of plumage, Thalassidroma oceanica 

 (Kuhl.) being, as far as I know, the only Petrel common to both he- 

 mispheres. But, while most of the northern Petrels have representative 

 species in the southern hemisphere, many of the southern ones find no 

 analogue in the northern hemisphere — e.g., P.gigantea (Gmel.); Dap- 

 tion Capensis (Lath.); Prion vittatus (Cuv.), Pelecanoides urinatrix 

 (Cuv.), &c. These facts make it appear probable that the northern 

 species crossed over the Equator from the southern hemisphere, per- 

 haps during the glacial period, and, having been isolated ever since, 

 have varied somewhat from the parent forms ; and the fact that in the 

 three cases I have mentioned two distinct species in the northern he- 

 misphere are closely related to one species in the southern hemi- 

 phere points also to the same conclusion. The great extent of land 

 in the northern hemisphere will probably explain why the genus Puf- 

 finus, whose habits are the least oceanic of any, has been so lai'gely de- 

 veloped in those seas, while that of Procellaria is restricted to two 

 closely allied species. The only two species of Procellaria at present 

 known to inhabit the tropical parts of the Pacific are also each repre- 

 sented in the Southern Ocean — viz., P. parvirostris (Peale) by P. 

 Coohii (Gray) j and P. rostrata (Peale) by P. Lessonii (Gam.); they 

 both, however, differ more in colour from their types than the Ai'ctic 

 ones do from theirs. Thalassidroma lineata (Peale), also from the torrid 

 zone of the Pacific, is a representative species of T. melanogastra 

 (Gould). 



The shape of the beak of the Petrels is another point well worthy 

 of notice — so formidable is it in appearance, so harmless in reality ; the 

 bite of the Albatross even being attended with but little inconvenience, 

 unless the point of the beak happens to catch the hand, as the whole of 

 the inner parts are quite soft, and yield to a slight pressure of the 

 finger. The natural food of the Petrel tribe consists of small fish, the 

 shell-less molluscs, small crustaceans, medusas, &c, which are swallowed 

 whole, and they do not therefore require a sharp beak fitted for cutting 

 or tearing ; for, although they may now and then regale themselves on 

 the body of a dead seal or whale, it is evident that before sealers and 

 whalers existed their opportunities for doing so must have been few 

 and far between — perhaps not more than once in their lives; and if 

 dead whales and seals were their usual food, they would find the tube 

 formed by the nostrils on the top of the beak of many of the species very 

 disadvantageous, as it must prevent them striking their beaks deep into 

 the blubber. 



Of what use, then, it may be asked, is the sharp curved point of the 

 beak ? I believe it to be of little or no use, but that it simply marks 

 their close relation to, perhaps their direct descent from, the Skuas 

 (Lesiris), who use it in their attacks upon Gulls. It cannot be said 



