130 Adams, Ecological Succession of Birds. [xl'rii 



White and Yellow Birch, and rarely Sugar Maple. Upon the dry 

 ridges, Jack Pine; and in burned areas, Aspen and Paper Birch. 

 Climate, seasonal changes very pronounced ; winters very long and 

 cold, and summers short and cool ; a relative humidity of about 

 80% in December and of about 70% in July (c/. Johnson, '07); 

 a mean temperature for January of 7.97° F. ; and for July, 62.24° 

 F. (Port Arthur data). Early, deep snows. Predaceaus animals, 

 as the Lynx, Marten, weasels, Red Squirrel and bats are directly 

 in competition with the birds for food, or prey upon the birds. 



The above environmental factors are dominant features and 

 give us a general picture of the conditions, largely in terms of com- 

 mon experience. In the life of the birds, however, a complete 

 reassortment and change of intensity in these factors occurs when 

 they are combined as habitats. The surrounding lake, the numer- 

 ous bays, small lakes and ponds compose the aquatic habitat and 

 make it a characteristic feature. The very irregular and extensive 

 shore line and limited beach area characterize the coastal border, 

 while inland, excepting the main bodies of the few larger lakes, 

 the encroachment of the bog vegetation upon the shores is such as 

 to prevent an extensive development of sandy open beaches. The 

 above mentioned habitats are open unforested areas ; the remainder 

 of the island, with the exceptions of the bare rocky ridges, the 

 clearings and burned over areas, are forested. Very extensive 

 swamp forests abound in the elongate valleys and the borders of the 

 water bodies, and are composed of Tamarack, Black Spruce and 

 Arbor Vitae. The mesophytic forest occurs on drained areas and is 

 characterized by Balsam Fir, White Spruce and Paper Birch; the 

 burned areas by second growths of aspens and Paper Birch. Then 

 there are also influences which are exerted upon the bird life in 

 general, as for example, migration. In this case, undoubtedly 

 both external conditions and the habits and the behavior must be 

 correlated. x\nother general and dominant influence should be 

 reiterated here, and that is that all open areas tend to become in- 

 vaded with vegetation and finally forested, whether they are lakes, 

 ponds, bogs, rock openings on the ridges, burns or clearings. The 

 mesophytic Balsam-spruce forest tends to monopolize all habitats, 

 and gives a definiteness to all succession upon the island. 



From a genetic standpoint the past and present dominance of the 



