446 A HISTORY OF BIRDS 



this migration we of course cannot say, but it is not difficult to 

 imagine members of each group using the higher and drier 

 surrounding country as a temporary resort, and ultimately 

 forsaking the older haunts to found new colonies where com- 

 petition perchance was less keen. At the present day, for ex- 

 ample, many of the Plover tribe pass at least part of the year 

 on the uplands, and the remainder by the sea or in the marshes. 

 The long legs of these two convergent forms, originally de- 

 veloped to enable their possessors to wade in search of food, 

 are now used as an aid to escape enemies before resorting to 

 flight. In the matter of the toes certain changes have taken 

 place in response to the new environment : originally of moder- 

 ate length, so as to support the weight of the body in soft 

 places, they have now become much shortened, thereby form- 

 ing more perfectly a cursorial function. 



As touching the sea-haunting habits of the Plover tribe. 

 As might be expected, some species rarely leave this habitat, 

 such as the aberrant Crab-plovers {Dromas) of E. Africa, Mada- 

 gascar and S. India, for example ; while the curious and aber- 

 rant Chionis or " Kelp-pigeon " of the Antarctic is even more 

 maritime. " It feeds," says Darwin, " on sea-weed and shells 

 on the tidal rocks. Although not web-footed, from some un- 

 accountable habit, it is frequently met with far out at sea. 

 This small family of birds is one of those which, from its varied 

 relations to other families, although at present offering only 

 difficulties to the systematic naturalist, ultimately may assist 

 in revealing the grand scheme, common to the present and past 

 ages, on which organised beings have been created." 



If this much-to-be-desired culmination has not yet been 

 reached, an approach thereto, which he probably at that time 

 did not foresee, has been made, inasmuch as these birds furnish 

 an undoubted link in the chain of evolution of the Auk tribe. 

 No one supposed, when Darwin wrote the words just quoted, 

 that the Auks were related to the Plovers. To-day this is 

 recognised as a fact ; but the lines along which the transforma- 

 tion took place, and the nidus from which they arose has 

 always been a difficult problem. But there can be little room 

 for doubt but that they arose, if not from this family, at least 

 from some ancestral Plover having similar habits to those of 

 the " Kelp-pigeon ". Presently the peculiar features of the Auk 



