^"l908^^] Adams, PJrnl'yjical Succession of Birds. 129 



species may be noted, with a corresponding decrease in another; 

 and this proportion may continue to change until the intruder be- 

 comes dominant and the rival form may disappear entirely. 

 This process of change, as a rule, is not limited to a single species, 

 but usually involves several or all of the members of the association, 

 as when a dune invades a swamp and the swamp birds are com- 

 pletely replaced by those frequenting the sand dunes. 



2. Succession on Isle Roijale. AVith these preliminary considera- 

 tions in mind, we will turn to the ecological succession of bird life 

 ui)on Isle Royale, I^ake Su])erior. The field work upon the island 

 Avas carried on by a party from the University Museum of the 

 University of Michigan, under the direction of the writer. Aside 

 from succession, the general ecological relations of the birds were 

 studied by Otto INIcCreary and INIax M. Peet, and elsewhere detailed 

 descriptions of the region and detailed notes will be published. The 

 writer has based his main records of habitat preference upon their 

 work. For this outline of succession only the primary features of 

 the location need be given. 



In the present treatment an attempt will be made to follow the 

 genetic succession, at least in its broader outlines. Various quali- 

 fications and reservations have been made, and others Mill follow, 

 so it is hoped that no confusion will be produced by this method of 

 treatment. 



Geographicalhj, Isle Koyale, Michigan, is an island in Lake 

 Superior, near the North Shore, not far from Port Arthur, Ontario. 

 The topography forms a part of an ancient peneplain of moderate 

 relief, glaciated and with an abundance of elongated low ridges 

 and valleys with numerous water basins. The soil, which is locally 

 absent, is generally humic or mixed in character, bordering and in 

 the depressions; but is mineral, stony and residual elsewdiere. 

 The combined shore and beaches are extensive, largely stony and 

 gravelly, and contain but little sand; much of the shore line is 

 rocky and precipitous; many outlying islands. Vegetation, her- 

 baceous in shallow inland waters and as a ground cover except 

 where the shade is too dense, and upon rocks; -shrubs on protected 

 beaches, in more open places in the forest and in burns; the forest 

 consists of Tamarack, Black Spruce and Arbor Vitae in bogs; and 

 elsewhere in mesophytic conditions of Balsam Fir, Arbor Vitie, 



