Historically, the Illinois River Valley (IRV) and its flood plain wetlands provided quality habitat for migrating ducks during fall and spring. Several factors have reduced or degraded IRV wetlands over the last century including: diversion of water from Lake Michigan to the Illinois River, creation of drainage and levee districts that drained wetlands for agriculture, and increased summer flooding due to navigation dams and reduced water storage capacity. Swan Lake is a 920 ha backwater wetland adjacent to the Illinois River near the confluence of the Mississippi River. Within years of the installation the Alton Dam on the Mississippi River, sedimentation in the lake increased from flood events on the Illinois River and runoff from adjacent agricultural lands. The increase in sedimentation decreased water quality, aquatic plant growth, and lake depth, thereby reducing Swan Lake's value as fish and wildlife habitat. To address the various environmental problems on Swan Lake, a Habitat Rehabilitation and Enhancement Project (HREP) was initiated by the USACE in 1994. The HREP at Swan Lake intended to improve habitat for ducks and fish. We evaluated the success of the HREP on improving habitat for ducks by comparing peak abundance and foraging behavior of ducks between pre- and post HREP implementation. As predicted peak abundance, duck use days, and feeding intensity increased. To our surprise, however, these 3 factors also increased on neighboring wetland habitats that were unaffected by the HREP. We use optimal foraging theory to explain the change in abundance and behavior on the impacted and non-impacted wetlands and suggest that juxtaposition of wetlands is an important consideration when restoring wetlands because enhancement of one wetland may have positive impacts to wildlife on neighboring wetlands.
