MIGRATION. 237 



wind and storm, and perils innumerable? The perils which 

 birds encounter in their migrations are inconceivable to those 

 unacquainted with the facts. Overcome by adverse winds 

 and storms of great severity, immense numbers become 

 exhausted and perish, as is shown by the numbers of the 

 small land-birds drifting on to the shores of the Great 

 Lakes after very severe storms. Attracted and dazed by 

 the light-houses stationed here and there, so many dash 

 their lives out against them as to render these points of 

 incalculable interest to the observer. The continuous net- 

 work of telegraph wires spread over the country maims 

 and destroys countless numbers. After heavy storms, 

 during their migrations, hundreds of Ducks have been 

 picked up dead on a single morning on Niagara River, 

 below the Falls, they having flown into the great cataract 

 and perished. 



Again, the same author says: "If we go back only as 

 far as the height of the glacial epoch, there is reason to 

 believe that all North America, as far south as about 40^^ 

 north latitude, was covered with an almost continuous and 

 perennial ice-sheet. At this time the migratory birds would 

 extend up to this barrier (which would probably terminate 

 in the midst of luxuriant vegetation, just as the glaciers of 

 Switzerland now often terminate amid forests and corn- 

 fields), and as the cold decreased and the ice retired almost 

 imperceptibly year by year, would follow it up farther and 

 farther, according as the peculiarities of vegetation and 

 insect-food were more or less suited to their several consti- 

 tutions." The only possible interpretation of this passage 

 would seem to be that the birds, being held in the south by 

 the glacial epoch, followed up the recession of the cold at 

 the closing of that period, and ever since have kept up the 

 same movement in annual accommodation to cold and ice^ 



