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INTRODUCTION. 



Of the many problems in the scientific study of birds, none 

 is more suggestive than that of local distribution. One walks 

 through the open fields in the month of June, and finds there a 

 concourse of birds that he knows will be found nowhere else. 

 There are the Savannah, Vesper, and Grasshopper Sparrows, 

 Bobolinks, and Meadowlarks, birds which are said to be 

 typical of such an environment. Passing on to the overgrown 

 borders of a wooded area, he finds Song Sparrows, Yellow 

 Warblers, Redstarts, Red-eyed Vireos, and Catbirds — a dif- 

 ferent assemblage. Thus, in passing from one distinct type 

 of environment to another, he passes from one distinct group 

 of birds to another. The botanists have long recognized the 

 importance of similar associations or societies of plants, and 

 have done much toward determining their controlling factors. 

 Environments have been intensively studied, and their 

 meteorological and physiographic conditions determined. 

 The various factors imposed by organic and chemical agencies 

 have been investigated, and the resulting adaptations of 

 species and individuals have been correlated. The whole 

 has placed the botanist on terms of intimacy with the natural 

 Hfe processes of the objects which he studies — a state not yet 

 attained by the zoologist. For the student of animal ecology 

 there remains an almost virgin field. Especially is this true 

 in the study of birds. Here much preliminary work has been 

 done in the way of collecting data concerning distribution, 

 migration, and variation. Outlines of the life histories of most 

 of the birds have been formulated. In a few instances en- 

 vironments have been described with appended lists of bird 

 inhabitants. This is valuable and necessary, but far from 

 final. What has been done toward the correlation of these 

 various factors? From almost any volume on birds one can 

 very easily tabulate all of the known differences in structure 

 between the Vesper, Song, and Swamp Sparrows. He can 

 find described at some length the habitat or environment in 

 which each is found. But where can he find set forth the 

 factors which determine that one bird shall inhabit the open 



