Page:The Zoologist, 3rd series, vol 1 (1877).djvu/42

16 To account for the appearance of North American birds in this country is not so easy. I was at one time inclined to believe that the majority of them must find their way here from Greenland viâ Iceland, but the investigations of Professor Spencer Baird have led me to alter this opinion, and to concur for the present in his own view that their appearance here is due principally, if not entirely, to the agency of the winds at the period of their migrations. Prof Baird's remarks on this subject are so extremely interesting and at the same time so instructive, that they may be here appropriately quoted. After some pertinent observations on zoological geography and the general principles of distribution to which he has been led by an examination of the large collection of specimens in the Museum of the Smithsonian Institution, he proceeds to deal in detail with the migration of North American birds, and referring to the species which are reported to have occurred in England, he says:—

"Birds of North America rarely, if ever, reach England from Greenland by direct spontaneous migration by way of Iceland, as shown by the fact that only three of the American birds occurring in Greenland are found in Iceland, and that few of the American species observed in Europe are found in Greenland at all. Most specimens of American birds recorded as found in Europe were taken in England (about fifty out of sixty-nine), some of them in Heligoland, very few on the Continent (land-birds in only five instances). In nearly all cases these specimens belonged to species abundant during summer in New England and the Eastern Provinces of British America. In a great majority of cases the occurrence of American birds in England, Heligoland, and the Bermudas has been in the autumnal months. The clue to these peculiarities attending the interchange of species of the two continents will be found in the study of the laws of the winds of the northern hemisphere, as developed by Prof. Henry and Prof. Coffin. These gentlemen have shown that 'the resultant motion of the surface atmosphere, between latitudes 32° and 58° in North America, is from the west, the belt being twenty degrees wide, and its greatest intensity in the latitude of 45°. This, however, must oscillate north and south at different seasons of the year with the varying declination of the sun. South of this belt, in Georgia, Louisiana, &c., the country is influenced, at certain seasons of the year, by the north-east trade winds, and north of the same belt by the polar winds, which, on account of the rotation of the earth, tend to take a direction