THE NATURAL HISTORY SURVEY. II 



Illinois rivers. This region of our area is much higher and its 

 influence is shown very plainly among certain varieties of bird 

 life. The Great Blue Heron nests in great numbers in the tall 

 timber along the more secluded portions of the Desplaines River, 

 while only a very few are to be found in the Calumet Region. 

 Most of our records of Short-billed Marsh Wrens, Cerulean 

 Warblers, Yellow-throated Vireos, Lark Sparrows, hawks, owls 

 and other birds show that a very large number of species prefer 

 the former region, along the Desplaines River. In this region the 

 land is more heavily timbered and there are also tracts of rich 

 prairies and pastures. The altitude of Du Page County is much 

 higher, as a whole, than that of the Calumet Region and a large 

 portion is quite heavily timbered. This is just such an area as 

 is enjoyed by many birds. Directly east of this region, along 

 Lake Michigan, we find deep ravines which afford shelter to 

 many of our birds during migration. The city of Chicago, and 

 Calumet, Hyde, Wolf and George lakes lie in the center of this 

 great basin formed by the areas just described. This tract is but 

 slightly above the level of Lake Michigan. 



CLIMATIC INFLUENCES. 



The fact that Chicago has a greater per centum of lake winds 

 than any other station on the Great Lakes, as may be seen by 

 consulting the charts of the United States Signal Service, may 

 account for the large number of northern and maritirne species 

 of birds in which, during the migration periods, this region is 

 particularly rich. I will quote from Mr. E. W. Nelson's excel- 

 lent report on the climate of this area. He says : "Not only is 

 the influence of the Lake upon the fauna shown by the occurrence 

 of numerous species of birds, attracted by the presence of a large 

 body of water with its congenial surroundings, but the influence 

 of the Lake upon the climate and the vegetation in its immediate 

 vicinity, has a marked influence upon the list of summer residents. 

 "As is well known, the country bordering upon the Great 

 Lakes • has an average lower temperature during the summer, 

 and a higher temperature during the winter, than the surrounding 

 districts. This has a decided effect upon the movements and 

 distribution of the birds in the vicinity of these large bodies' 

 of water. This influence is shown in a retardation, often of a 

 week or more, in the spring migration, and in the scarcity^ of 



