H^MATOPUS. 



299 



the Pacific coast of the New World. The South-American Black Oystercatcher (H. niger 

 ater) is evidently the result of an emigration from the range of the preceding species, which 

 has caused a colony to cross the Tropics and establish themselves as residents on the coasts 

 of Chili, Patagonia, and the Falkland Islands ; but the isolation of the two colonies thus 

 produced does not appear to have lasted quite long enough for the complete differentiation 

 of the two forms. 



These two forms represent the Pacific New-World group of Oystercatchers, which 

 may be characterized as having the whole of the plumage black and the legs flesh-coloured. 



There yet remain for consideration two very closely allied Oystercatchers, and we have 

 yet undisposed of the route by way of the Pacific coast of the Old World. If the con- 

 nection between them be a historical one, the ancestors of the Australian Black Oyster- 

 catcher (II unicolor) must have followed the mountainous coast of China, and have crossed 

 the too tropical Malay Archipelago to settle in Australia and New Zealand. 



Instead of retracing their steps to the Behring Sea, the surplus population of the 

 Australian Black Oystercatchers appear to have emigrated westwards to South Africa, 

 which has resulted in a nearly allied, and not yet more than subspecifically distinct, race, 

 the African Black Oystercatcher (//. unicolor capensis). 



These two forms represent the Pacific Old-World group of Oystercatchers, which may 

 be characterized as having the whole of the plumage black and the legs red. 



We have now attempted to trace the history of the American detachment of Oyster- 

 catchers, and we have tried to follow the fortunes of the other portion which retreated along 

 the shores of the Old World. The two American parties found a comparatively restricted 

 coast-line at their disposal, and both of them seem to have been glad enough to retrace their 

 steps, after the glacial climate had passed away, almost to the entrance of the Polar Sea. 

 The Asiatic party, on the other hand, found a practically unlimited extent of coast-line 

 suitable to their requirements, They seem to have had room and to spare in Australia, 

 South Africa, and on some of the numerous islands in the southern half of the Eastern 

 Hemisphere ; consequently they never had occasion to recross the line to occupy once more 

 their old route of emigration on the Pacific coast of Asia. But although they wandered 

 to the other side of the world, the fact that the two Pacific parties travelled in company 

 for more than two thousand miles further than the two Atlantic parties could have done 

 has produced precisely the results which we anticipated : the Pacific Old- World Oyster- 

 catchers scarcely differ from the Pacific New-World Oystercatchers in anything beyond the 

 colour of their legs. 



This completes the list of Oystercatchers, a group of birds whose peculiarities of colour 

 and whose geographical distribution bear unmistakable evidence of the Glacial Epoch 

 almost as obvious as the geological evidence. We can trace almost with certainty the 

 routes which the various parties took on their emigration from the shores of the Polar Basin. 

 The great invasion of Europe by Pallas's Sand-Grouse in 1863 is almost the only instance 

 of sudden migration which the present generation of ornithologists have witnessed, but the 



2 Q 2 



Emigration 

 along Pacific 

 coast of 

 Asia. 



