Birds Common to Europe mid North America. 1 83 



might be fairly considered distinct species; moreover, that the 

 higher the latitude of the place of birth of any species, the 

 larger will be its size ; for example, as I will show presently, 

 enormous flights of the well-known golden plover, breed in 

 Canada, many pushing up into the Arctic Regions, of these 

 the individuals born in the former are relatively smaller than 

 the specimens reared further northwards. Much evidently de- 

 pends on the amount of food and the distance gone over in the 

 migrations, which cause a greater development of the muscles, 

 the bill and feet participating in the laws which regulate the 

 development of organs in connection with the animal's re- 

 quirements. As to coloration, it has been frequently observed 

 that birds frequenting coasts are darker in plumage than those 

 of the interior ; hence the bleached appearance of many of 

 the denizens of the desert tracts, as observed in the larks and 

 other birds of Egypt, etc., as compared with the darker hues 

 of the denizens of forests and of the umbrageous vegetation 

 of the tropics. 



I have stated that there are only about sixty species of 

 birds common to the northern continents of Europe, Asia, and 

 North America. Now with reference to birds common to the 

 Old and New Worlds. These are chiefly water birds, there 

 being only a very few land species — to wit, the golden eagle, 

 peregrine falcon, osprey, sea eagle, rough-legged buzzard, long- 

 eared, snowy, and hawk owls, sand martin, Bohemian chatterer, 

 pine grosbeak, redpoll, snow and Lapland buntings, raven (?), 

 willow grouse, and ptarmigan. Moreover, eliminating the 

 above, we find that nearly thirty- five land and about as many 

 water birds, strictly American, have turned up accidentally 

 from time to time in Europe, more especially in Great Britain ; 

 whereas in the interchange between Europe and America the 

 numbers are restricted to only a very few species, including 

 the white-rump and skylark among the land birds, and these, 

 with the exception of the lark, are met with in Greenland. 

 The causes of this marked discrepancy have been accounted 



