Perils of Migration 



The period of migration is a season full of peril for birds. Untold 

 thousands of the smaller migrants are destroyed each year by storms 

 and through attacks of predatory birds, mammals, and reptiles. If 

 each pair of adult birds should succeed in raising two fledglings to 

 maturity, the population of migratory birds would have a potential 

 annual increase of lOO percent and the world would soon be heavily 

 overpopulated with them. Since there is no such increase it is evident 

 that the annual mortality from natural causes is heavy enough to keep 

 it in check. 



Storms 



Of the various factors limiting the abundance of birds, particularly 

 the smaller species, storms are the most potent. Special sufferers are 

 those birds that in crossing broad stretches of water are forced down 

 by a storm within reach of the waves. Such a catastrophe was once 

 seen from the deck of a vessel in the Gulf of Mexico, 30 miles off the 

 mouth of the Mississippi River. Great numbers of migrating birds, 

 chiefly warblers, had accomplished nearly 95 percent of their long 

 flight and were nearing land, when, caught by a norther against which 

 they were unable to contend, hundreds were forced into the waters of 

 the Gulf and drowned. On another occasion, on Lake Michigan, a 

 severe storm came up at a time when large numbers of migratory 

 birds were crossing and forced numerous victims into the waves. Dur- 

 ing the fall migration of 1906, when thousands of birds were crossing 

 Lake Huron, a sudden drop in temperature accompanied by a heavy 

 snowfall resulted in the death of incredible numbers. Literally thou- 

 sands were forced into the water and subsequently cast up along the 

 beaches, where in places their bodies were piled in windrows. On one 

 section of the beach the dead birds were estimated at 1,000 per mile, 

 and at another point at 5 times that number. Most of them were species 

 that rank among our most desirable birds as destroyers of insects and 

 weed seeds, including slate-colored juncos, tree sparrows, white- 

 throated sparrows, swamp sparrows, winter wrens, and golden- 

 crowned kinglets, together with many brown creepers, hermit thrushes, 

 warblers, vireos, and others. 



Of all species of North American birds, the Lapland longspur seems 

 to be the most frequent victim of mass destruction from storms. These 



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