ECOLOGY OF ISLE ROYALB. ' 125 



the succession of the vegetation, a factor of the utmost importance in 

 the study of avain succession. 



While considering Townsend's results, it may be well to outline 

 briefly a general succession of bird life along the shore as indicated 

 by his records. It is evident from the map accompanying his volume 

 that the currents and waves are constantly modifying the coast line 

 and forming spits, bars and islands ; and that the barrier beach area is 

 increasing, and thus tending to become continuous at the expense of 

 some of the ocean habitat. As the continuity of the beach develops, 

 the area, of swamp land behind it tends to increase and; tlius to further 

 restrict the open water and increase the swamp haibitat. The beach 

 sands, once free from the waves or ground water, are caught up bv the 

 winds to form dunes, and may migrate into the swamps and thus trans- 

 form them. Thus with the extension of the beach the sea birds are re- 

 placed in dominance by the shore birds, and a succession is produced. 



In a similar manner the dunes encroach upon the swamp, and swamp 

 birds are succeeded by those of the dunes. As the wandering dunes 

 become anchored by vegetation and forests grow upon theta, still other 

 birds will invade them,. Thus all stages may be expected, from ocean 

 to beach birds, onward to those characteristic of wandering and fixed 

 forested dunes. These relations are outlined simply to indicate the 

 problem and its causes, which need detailed investigation. 



In Michigan a few habitat studies have been made. One in the Por- 

 cupine Mountains, on the south shore of Lake Superior, and another on 

 Isle Eoyale. Both are by McCreary ; the paper on the latter area is pub- 

 lished in this volume. The summer birds of the Porcupine Mountains are 

 listed (McCreary '06) by selected' localities and the habitat preferences 

 are discussed as follows: water birds, birds frequenting the shores and 

 banks of streams, birds frequenting grassy meadows and alders, birds 

 frequenting tamarack and cedar swamps, birds frequenting hemlocks 

 and maples, and birds frequenting the cliff and mountain top. In its 

 emphasis upon habitat preference this paper is the only one so far seen 

 which at all approaches Townsend's discussion of this subject. Mc- 

 Creary's work was done without a knowledge of Townsend's. 



In southeastern Michigan,, Brown ('06) made a locality study and 

 outlines the habitats as follows : birds found in orchards, birds of the 

 open woods, birds of the open fields, birds of the thicket, and birds of 

 the marshes and river. Brown's paper is internalediate in character 

 between the preceding papers and those of an economic nature, to be 

 mentioned later, because the area studied has been so much influenced 

 by man. 



There are a few papers which, although primarily faunistic or geo- 

 graphic, contain habitat data. Such, for example, is Ridgway's ('74) 

 discussion of the birds of the Wabash Valley and ('89) the birds of 

 the Illinois prairie (pp. 13-16). An exceptionally good paper of this 

 character on the Louisiana birds is by Beyer, Allison and Kopman ('06), 

 although its aim and nuethod of treatment differs from that of Town- 

 send. The bird life is, however, closely correlated with the vegetation 

 and the physical conditions of the State. 



The papers previously mentioned have been written from a regional 

 standpoint. The study however of all the various conditions frequented 



