Evolution of Backwater Lakes along the Illinois River with Waterfowl as a Sentinel of Change

Backwater lakes within the Illinois River Valley (IRV) historically provided habitat for >20% of the Mississippi Flyway’s mallard (Anas platyrhynchos) population during autumn, but use has declined more than 80% since the 1950s. Similarly and more dramatically, lesser scaup (Ayathya affinis) use has declined more than 90% since the 1970s. Despite declines in species historically common and widespread loss of aquatic vegetation communities in the region, use and peak abundances of several other species of waterfowl have dramatically increased within the last decade. For example, total use days for ducks (29,681,598 use days) during autumn 2013 were the highest recorded since 1985 in the IRV. Similarly, peak abundances of northern pintail (Anas acuta), American green-winged teal (A. carolinensis), gadwall (A. strepera), and northern shoveler (A. clypeata) were the greatest recorded since initiation of aerial surveys in 1948. Even diving ducks have increased in recent years. We estimated a peak abundance of 118,830 diving ducks along the Illinois River in 2013, which was 258% above the 5-year average. While species traditionally common, such as lesser scaup, have not recovered to historical use levels, other species have apparently responded to recent habitat restoration in the region (e.g., ring-necked duck [Aythya collaris] and ruddy duck [Oxyura jamaicensis; highest peak abundance ever recorded in 2013]). Waterfowl abundances in the IRV have increased concurrent with restoration of several backwater lakes in the region which provide a diversity of aquatic vegetation communities previously eliminated from the region. For example, Emiquon Preserve is a restored wetland complex that accounts for more than 30% of the total waterbird use days in the IRV. We will describe backwater lake restoration strategies used, illustrate how a few signature restoration projects can change patterns of waterfowl use for an entire region, and recommend indicators to assess restoration success and trajectory.