NUMENIUS. 319 



The present geographical distribution of the Curlews can only be accounted for on the 

 assumption that they were originally inhabitants of the Polar Basin. Of the eleven species 

 and subspecies which comprise the genus Numenius, two, N. borealis and N. hudsonicus, 

 are exclusively Arctic during the breeding-season. N. tenuirostris, breeding in the basin 

 of the Mediterranean, might be called semi-tropic, but all the others may fairly be regarded 

 as Arctic or Semi- Arctic. 



The species belonging to the genus Numenius naturally fall into five groups, which Division 

 probably escaped from the Polar Basin by five different routes, when the coming on of the groups. 

 Post-Pliocene Glacial Epoch drove them south . 



The first group to be considered may be described as Pale-rumped Curlews. They 

 may be diagnosed as having the lower back white, or white more or less streaked with 

 brown, but with no mesial line on the crown. They represent the Atlantic-coast Curlews 

 of the Old World, and consist of two species, one of which is divisible into two subspecies. 

 The Pale-rumped Curlews, being represented by two species in Europe, one in Asia, 

 and being entirely absent from America, doubtless escaped from the ice by way of the Kara 

 Sea, along the European coast, and up some of the great rivers of Western Siberia. 



The fact that the range of N. tenuirostris does not extend further east than the Ural 

 Mountains confirms the theory that the Pale-rumped Curlews escaped from the Polar Basin 

 along the Atlantic shores of Europe. At the height of the Glacial Epoch they were 

 probably isolated in two colonies, one in West Africa and the other in the valley of the 

 Nile, for a period long enough to make them specifically distinct. When the Glacial 

 Epoch had passed away, the West-African colony spread over the basin of the Mediterranean, 

 whilst the East- African colony extended its summer range over the head of its ally east 

 and west, until it finally extended from the Atlantic to the Pacific, whilst its winter range 

 covered South Africa, and afterwards reached India, Burma, and the islands of the Malay 

 Archipelago. The complete isolation of the African and Asian winter colonies of the 

 Common Curlew produced variation in the species ; but the uninterrupted area of their 

 distribution in summer, combined with the much shorter period during which they have 

 been isolated, have prevented the birds from these colonies from becoming completely 

 differentiated. 



The second group comprises the Pale-rumped Whimbrels, which may be diagnosed as 

 having the lower back and rump white, more or less streaked with brown, but always 

 contrasting with the darker mantle, and the crown plain brown, with a pale mesial line. 

 They represent the birds which left the Polar Basin along the east coast of Greenland, and, 

 finding the west coast already occupied, crossed over to Europe by Iceland and the Faroes. 

 From their present arctic habits it seems probable that they never crossed the Mediterranean, 

 but remained during the Glacial Epoch on the outskirts of the ice, which they followed on 

 its retreat, until they finally spread over the Arctic Region of the Old World. 



The Whimbrel is so common in Iceland and the Faroes that it is natural to suppose 

 that it emigrated to the Arctic Regions of the Old World by way of those islands along the 



