ECOLOGY OF ISLE ROY ALE. 113 



northeasterly direction and died away in a southwesterly one. Cer- 

 tain birds, as the Thick-billed Red-wing Blackbird and Lincoln 

 Sparrow, which were found commonly at the island, are very 

 rare or do not occur at all in the region directly south 

 or southeast of it. The Thick-billed Red-wing has never been taken 

 at any point in southern Michigan. These birds, being of western origin, 

 have gradually worked their way east where they have found suitable 

 breeding groimds, but it seems probable that in their fall migration they 

 move westward and join the throng passing down the migration roiite 

 traversed by their ancestors. It seems probable that the greater portion 

 of the migrants which leave Isle Royale', moving in a southwesterly 

 direction, continue thus until they reach the Mississippi Valley, where 

 they are joined by birds from other regions, and all move down this great 

 highway of bird migration. 



It was observed that nearly all the large bird waves were associated 

 with northwest winds. As the birds probably take a southwest course 

 this gives them the beam wind which seems to be most favorable for 

 their flight. Of course it was impossible to tell from what direction 

 the birds came to Isle Royale, but it seems reasonable that they should 

 choose a beam wind when leaving the mainland, since they arrived 

 shortly after at the island flying with such a wind. If this proves 

 to be true, the majority of the birds coming to Isle Royale are from 

 the north or northeast. 



The data for the supposed route to Keweenaw Point is slight com- 

 pared with that for the southwesitern one. Two species, the Rusty 

 Graokle and the American Pipit, were observed migrating in this direc- 

 tion. During their flight the wind was from the northeast giving them 

 the beam wind which a number of observers have noted to be the one 

 preferred by hawks and gulls during their migration. Under "Perils 

 of Migration" an instance is cited where a number of birds were caught 

 by a storm while crossing to the east of the island and were driven 

 to Washington Harbor. These birds were possibly crossing to Kewee- 

 naw Point. Probably the majority of the birds which strike this point 

 are from regions lying to the northeast of it, and arrive there on nortli- 

 west winds as do those birds which mtigrate across Isle Royale. The 

 theory that many birds skirt the Great Lalies, as brought out by ' 

 Tavemer, explains the absence of several species from Southern Mich- 

 igan which is not done by the discussion of the routes from Isle Royale. 



VII. THE PERILS OF MIGRATION. 



Dixon in his "Migration of Birds," divides the perils of migration 

 into three important classes: first, those arising from fatigue due to 

 the mechanical part of season-flight; second, those arising from the 

 natural enemies of each species; and third, those arising from blunders 

 and fatalities on the way. These three classes were observed in vary- 

 ing degree during the fall migration at Washington Harbor. 



1. Fatigue. Between the north shore of Lake Superior and Isle 

 Royale, the distance is so short that unless unfavorable winds inter- 

 cept them the older birds would have little trouble from fatigue due 

 to the simple operation of flight; but the young, which often commence 

 migration soon after being able to fly, would experience considerable 

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