CHARADEIIDJE. 



67 



Climatic dis- 

 tribution. 



characters are correlated with others of much greater importance, which are only omitted 

 in consequence of a difficulty in clearly defining them. 



Although there cannot be much doubt that the group of species which form the 

 subfamily Charadriinse had an Arctic origin, only 6 species can now be regarded as 

 Arctic. No fewer than 50 species or subspecies breed in the Temperate Regions, in 

 climates of which the mean temperature of July in the northern hemisphere and that of 

 January in the southern hemisphere (dates which may be regarded as the height of the 

 breeding-season in each) varies from 60° to 77°. It is quite possible that during the 

 Pliocene age this temperature may have been the normal degree of heat in the Arctic 

 Regions, though the mean temperature of July now varies in that district according to 

 latitude from only 40° to 60°. The remaining 48 species or subspecies of the Charadriinae 

 have succeeded in adapting themselves to a tropical climate, where the mean temperature 

 of the two months selected varies from 77° to 90°. It must, however, be borne in mind 

 that in the tropics the date of the breeding-season of these birds varies locally to a 

 remarkable degree, and frequently extends over a much longer period than a month 1 . 



None of the Charadriinse are forest-birds, and many of them still retain what appears Habits 

 to me to have been their habit so long ago as the Pliocene Age — the habit of frequenting 

 the sea-shore, where they find abundance of food on the sandy beach or on the mud-flats 

 left exposed at low tide. A few seem to have slightly modified this habit so far as to seek 

 their food on the banks of rivers and lakes rather than on the sea-shore. Some find most 

 of their food on marshy swamps ; but the greater number of species belonging to this 

 subfamily appear to have been forced, in the struggle for existence, to adapt themselves to 

 a life on dry arid plains. A still greater divergence from their original habits must have 

 been achieved by the Pratincoles, who actually obtain most of their food on the wing like 

 Swallows. 



The fact that out of 104 species or subspecies only 19 are found in the New World, 

 and that out of 6 genera 3 are entirely unrepresented on the American continent, is a 

 strong argument for coming to the conclusion that this subfamily represents a natural 

 group, the common ancestors of which had already been isolated and differentiated from 

 their allies who lived on the shores of the Polar Basin in the Pliocene Age. We may 

 perhaps follow the argument a step further, and suggest the probability that the great 

 Asiatic steppes was the locality where the subfamily Charadriinae was isolated and 

 differentiated, where its members changed their habits, and that the descendants of some 

 of them, who are now shore-feeding birds, have not so much retained their ancestral habits 

 as reverted back to them. 



The species contained in this subfamily have been distributed amongst no fewer than 



Ancient 

 home. 



Pseudo- 

 genera. 



1 Of the breeding of the Cream-coloured Courser (Cursorius gallicus) Hume writes (' Nests and Eggs of 

 Indian Birds,' p. 564) : — " July was the month in which I found them " (the eggs), " and it is in this month 

 generally that the great bulk are found ; but the Eian has taken them from the middle of March to the 

 middle of August, and the laying-season varies a good deal according to the rains." 



k2 



