^°190^^^] Adams, Ecological Succession of Birds. 137 



habitat is only extensive in the aggregate. With the presence of the 

 open aspen and birch woods, the following society is likely to be 

 characteristic: — Jiinco, Oven Bird, Red-eyed Vireo, Chipping 

 Sparrow, AVhite-throated Sparrow, Flicker, Cedar Washing, Wil- 

 son's Thrush and the Chickadee. As the deciduous trees are re- 

 placed by the open encroaching conifer forest, the Song Sparrow, 

 the Nashville, Myrtle and Black-throated Green Warblers and 

 Wilson's and Olive-backed Thrushes, which frequent the forest 

 margins, increase in abundance. The Oven Bird has an extensive 

 northern range from Labrador into the Yukon Valley and may well 

 have been a very early pioneer upon the island as the aspens and 

 birches were probably the first broad-leaved tree arrivals. From 

 the above it is seen that this means an extensive variety, but as the 

 dominance of the climax forest encroaches this number again 

 becomes reduced. 



The composition of the society varies somewhat, depending upon 

 the surroundings, as proximity of the present shore or distance 

 from it. ]\Iany of these openings are continuous with the present 

 beach. It is not improbable that this was a prominent society 

 whenever the waters fell rapidly from the island between rather 

 stationary levels. This has been a society decidedly on the decline 

 with the encroachment of the forest. 



Probably this association varies considerably in its composition, 

 and has done so in the ])ast; l)ut its main features are fairly constant. 

 These variations seem likely, through the influence of openings pro- 

 duced by fires which, when extensive, may have caused a new 

 equilibrium among those species frequenting openings. 



The Burned Area dissociation. 



This phase should perhaps be considered as supplementary to the 

 aspen-birch association just considered. A fire brings about a 

 reversal of conditions through the destruction of the forest, and in 

 some cases, a part of the soil as well. As there are all degrees of 

 extent and completeness in this process, there is a corresponding 

 variation in the details of the resulting succession, at least in its 

 early stages. It is only when there is a very complete destruction 

 of the vegetation that the continuity with former occupancy is 

 wholly broken. 



