208 



MIGRATION 



No other biological field numbers so many and such ardent amateurs 

 as ornithology, and it was perhaps inevitable that the mystery of 

 migration should loom far too large in the consideration of the theme. 

 Even professional students have too often appeared sympathetic with 



Fig. 49. — Distribution and migration of the golden plover, Pluvialis dominica 

 (Miill). Adults of the eastern form (P. d. dominica) migrate across north- 

 eastern Canada and then by a non-stop flight reach South America. In spring 

 they return by way of the Mississippi Valley. Their entire route is therefore 

 in the form of a great ellipse with a major axis of 8,000 miles and a minor axis 

 of about 2,000 miles. The Pacific golden plovers {P. d. julva), which breed in 

 Alaska, apparently make a non-stop flight across the ocean to Hawaii, the Mar- 

 quesas Islands, and the Low Archipelago, returning in spring over the same 

 route. (After Lincoln, 1935.) 



views such as those of Lucanus (1922), who resorts to an incompre- 

 hensible migratory impulse that requires no particular external stimu- 

 lus and an instinct that determines direction automatically. Diametri- 

 cally opposed is the attitude of Nicholson (1929), Grinnell (1931), 



