138 MICHIGAN SURVEY, 19fl(8. 



ciations which, while they will vary in their changes, yet all tend to con- 

 verge in harmony with the dominant factors. Th&se conditions migrate 

 or radiate from the highest land. On the other hand, the inland marginal 

 zones, which border the smaller water bodies, migrate Inwardly; and 

 being closed areas, tend to become extinct. This marginal zone, parti- 

 cularly beyond the upper beach, forms one of the most interesting and 

 complex conditions found upon the island. lt>is not an ecological unit, 

 but is composed of several of them. This is where most of the con- 

 fusion arises in actual field work of habitat studies. 



&. The Shore and Marsh Association anil, HaMtat. 



As the area of the islands expanded and the shore line was lengthen- 

 ed, the habitat for shore birds increased ; but the steep and rocky shores 

 were unfavorable for the development of beaches because loose rock, as 

 tools for the waves, was limited in amount. The local character of the 

 shingle and gravel to-day found in the various coves cleariy indicates 

 their local origin; and much the same conditions have obtained in the 

 past. On account of these conditions, the sandy beaches are very con- 

 spicuously absent. The dynamic tendencies of the beach are those 

 which cause the extension or restriction of the aquatic and beach 

 habitats, supplemented by the drift which is tossed upon the shore. 

 Where there is shallow water, and mud accumulates, favorable condi- 

 tions are furnished for invertebrate food for birds. Inland, the numer- 

 ous lakes, ponds and marshes furnish shore conditions which tend to 

 become extinct through drainage or overgrowth of the vegetation, except 

 in those parts of the larger lakes where wave action tends to scatter 

 such accumulations as rapidly as formed, or to prevent its formation 

 altogether. 



Although observations on this subject are quite limited, yet it seems 

 fairly safe to consider the Spotted and Solitary Sandpipers as char- 

 acteristic birds of this association. Upon such a rocky coast, sandy and 

 gravelly beaches are quite exceptional and are confined to protected 

 ooves. Additional diversity is produced where small streams enter 

 these coves and produce deltas. 



Little is gained by sharply segregating the marsh and shore birds, 

 althoug'h the marsh birds show a preference for conditions better 

 represented or correlated with topographically older coasts, pro- 

 tected and inland conditions. Attention should be directed, how- 

 ever, to the significant fact that successions initiated with such 

 diversity will produce a variation in the composition of the associa- 

 tions. Also that so far as possible these variations should be con- 

 sidered comparatively and synthetically in reconstructing and antici- 

 pating successions. 



The American Bittern, Lesser Yellow-legs, Swamp Spai-row and 

 Marsh. Hawk belong, to this society of marsh . birds. As in the case of 

 the aquatic association, these birds generally nest in close proximity 

 or entirely within these shore or marsh conditions. Still other species 

 frequent this belt to feed, as it is an open area.; but their presence is 

 mainly conditioned by the adjacent shrubs or forest. The very limited 

 number of species in the aquatic amd shore associations is worthy of 

 particular mention. 



