8 



NORTH AMERICAN FAUNA 73 



deposits and includes numerous high, rounded hills composed of more 

 resistant bedrock. Geology of this region is primarily highly resistant Pre- 

 cambrian igneous rock, quite unlike southern regions of the Valley. Original 

 vegetation of the Northern Highland was composed almost exclusively of 

 pine forest and coniferous bogs. Presently, the pine forest exists only as 

 scattered remnants interspersed throughout extensive mixed second growth 

 deciduous and coniferous forest. Large lakes and extensive bogs are charac- 

 teristic of the Northern Highland. 



This brief discussion of the major physiographic regions of the St. Croix 

 River Valley points out both similarities and differences between the sys- 

 tems developed for each State. For the sake of convenience and clarity in 

 describing bird occurrence and distribution, I have combined both systems. 

 Thus, throughout this report reference to the Western Upland will include 

 the Wisconsin areas outUned in Martin (1932) and the Southern Oak Barrens 

 region of Minnesota described by Kratz and Jensen (1977). The Central Plain 

 will include the Wisconsin areas outlined and those areas of Chisago and 

 Washington counties included in the Mississippi River Sand Plains and the 

 Grantsburg Section. Reference to the Northern Highland will include the 

 Wisconsin areas and the Mille Lacs Section in Pine County. These agree 

 closely with the physiographic regions used by the U.S. Fish and WildUfe 

 Service s Breeding Bird Survey (BBS; Bystrak 1979). 



Habitats and Bird Distribution 



Within the Valley, a wide range of vegetational communities are available 

 to birds: deciduous and coniferous forest, wetlands, agricultural lands, and 

 urban-residential areas. Original vegetation of the Valley as described by 

 Curtis (1959) and Marschner (1930) included Tall Grass Prairie and Oak 

 Savannah in the Western Upland, Southern Hardwood Forest (primarily 

 oak) and Tall Grass Prairie in the Central Plain, and mixed Coniferous- De- 

 ciduous Forest association in the Northern Highland (Fig. 3). Much of the 

 bed of Glacial Lake Grantsburg was composed of relatively sterile jack pine 

 and oak forest. (Scientific names of plants are given in Appendix A.) 



Man's presence has had a profound impact on the composition, distribu- 

 tion, and extent of these major communities. The Tall Grass Prairie which 

 may have lapped at the shoulders of early settlers is now field and pastures. 

 The prairie is now confined to railroad rights-of-way and small odd corners 

 that would not accommodate a plow. The majestic white pine forest that 

 once blanketed most of the northern regions has been reduced to scattered 

 remnants. 



Habitat changes that adversely affect some bird species often encourage 

 expansion of other species. The clearing of forests of northern white pine has 

 allowed a second growth deciduous disclimax habitat type to develop. Land 

 clearing for agriculture was very important to the advance of the greater 

 prairie chicken (scientific names of birds are given in the species accounts) in 

 this region. Early accounts make vivid reference to the large number of 

 greater prairie chickens that occurred after moderate agricultural expan- 

 sion. However, the rapacious clearing that accompanied intensified agricul- 



