Effects of Water Fluctuation and Vegetation Change on Bird Populations, Particularly Waterfowl

In recent years reclamation activities in the Columbia Basin of Washington have resulted in profound changes in the character of the entire landscape throughout this region. The present study is an attempt to clarify some of the biological effects of impoundment behind O\u27Sullivan Dam in the Potholes area, Grant County (Johnsgard 1955b). In this area, a large expanse of moving sand dunes and a high water table are responsible for causing the formation of numerous small water areas, or potholes, between the dunes. The physical nature of the area and its limited potentialities have made it of little value to man in the past, and it has only been subjected to grazing. Except for this influence the area remained almost undisturbed until the completion of O\u27Sullivan Dam and the formation of Potholes Reservoir. The reservoir has flooded many of the potholes and has materially raised the levels of those remaining. The objective of this study is an attempt to correlate these water level and vegetational changes with changes in avian populations, thus providing a means of predicting future population changes and population potential. Ecologic work was begun in the area by Stanley W. Harris in 1950 (1952, 1954). His study provides an indication of biotic conditions before the impoundment caused a measurable effect on the wildlife of the area, and is concerned primarily with waterfowl. Breeding waterfowl of the area were also studied in 1952 by Allen J. Greene, U. S. Fish and Wildlife Service. From June 15 to August 15, 1953, and from February 15 to August 15, 1954, intensive field work for the present study was conducted in the area. Periodic surveys were also made during the fall and winter of 1953