Here are the most readily accessible books and articles about the Great Plains, High Plains, bison, and beaver.
Sherow, James E. The Grasslands of the United States This edited volume from ABC Cleo is a collection of overviews, essays, shorter articles, and case-studies about different aspects of the North American grasslands.
McHugh, Tom. Time of the Buffalo A great natural history about bison, readable and well illustrated.
Flores, Dan, “Bison Ecology and Bison Diplomacy” in the collection The Natural West.
Isenberg, Andrew The Destruction of the Bison Despite its title, this is a well-balanced account of bison and their predators.
Müller-Schwarze, Dietland, and Lixing Sun, The Beaver: Natural History of a Wetlands Engineer. More than you ever wanted to know about beavers, well written with nice illustrations.
McCarty, John D. Maverick Town: The Story of Old Tascosa is not an animal book per se, but he explains a great deal about the Canadian River Valley and how it looked prior to 1890.
Rathjen, Frederic, Texas Panhandle Frontier describes the region as it was before Anglo settlement began.
Of the books listed above, McCarty and Sherow may be a little difficult to find, but should be available through inter-library loan.