. The sportsman's British bird book . ween the members of the two groups being,as in so many similar instances, merely an adaptation to the samekind of existence. With the gulls and terns the auks agree in thewebbing of their toes, which is, however, only another adaptivecharacter, as well as in certain far more important features, such asthe structure of the bony palate of the skull, which is of the open as 190 AUK GROUP distinct from the closed type, the sHt-likc apertures of the nostrils inthe skull, and the forked shape assumed by the fcather-bcarin<j tract onthe lower part of the back.
. The sportsman's British bird book . ween the members of the two groups being,as in so many similar instances, merely an adaptation to the samekind of existence. With the gulls and terns the auks agree in thewebbing of their toes, which is, however, only another adaptivecharacter, as well as in certain far more important features, such asthe structure of the bony palate of the skull, which is of the open as 190 AUK GROUP distinct from the closed type, the sHt-likc apertures of the nostrils inthe skull, and the forked shape assumed by the fcather-bcarin<j tract onthe lower part of the back. In their peculiar bodily shape and up-right position when standing, due to the backward situation of thelegs, and the deep and highly compressed beak, as well as by theirextremely close and compact plumage, auks present, however, amarked contrast to the gulls and terns ; from which they also differvery decidedly in their habits, more especially the great developmentof the power of diving. Indeed, it is for the purpose of diving that. MObNT&D ih THE ROWLAHLf AARO STuC;iOS IN (;\(;i-: these birds arc so specially modified and differ so remarkably fromthe normal type. Auks are also characterised by the fact that theydeposit their eggs, which are pear-like in form, on a bare ledge ofrock, in a cranny, or in a hole burrowed by the bird itself, without theslightest attempt at a nest ; and that, as a rule, only a single egg, andthis of relatively large size, is laid by each female, while never morethan two eggs are incubated together. All the members of the groupare sea-birds, and are confined to the northern hemisphere, where theybreed in the sub-Arctic and Arctic zones, and in winter visit moresouthern latitudes, although never reaching any part of the Intlianregion or crossing the equator. Two moults in the year are character-istic of the group ; and it is a remarkable fact that among the , AUK OR RAZORBILL 191 in which the beak is ornamented by b
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