Energetic Carrying Capacity in the Upper Illinois River for Waterfowl

The Illinois River historically provided productive habitats for a variety of migratory birds, but management for commercial navigation, sedimentation, and increasing hydrologic variability has led to a reduction in aquatic vegetation and naturally-occurring foods foraged by waterfowl. The vast majority of aquatic vegetation disappeared between 1940 and 1960 and has not returned to most of its historical prevalence. The Dresden reach of the Illinois River is composed of the Kankakee and Des Plaines rivers which form the Illinois River at their confluence. The Dresden reach is productively different from the rest of the Illinois River because unlike other reaches, it is home to an abundance of seed-producing aquatic macrophytes important to waterfowl. Additionally, the Starved Rock reach, to a lesser extent, has also retained some of its aquatic vegetation. Energetic carrying capacities, duck energy days, and overall waterfowl food characterization have been well documented in the lower Illinois River valley, however little information exists to characterize energetic carrying capacity for waterfowl in the upper Illinois River. To determine energetic carrying capacity of seeds and tubers in the upper Illinois River, we collected benthic core samples from 20 locations in backwater lakes connected to the river, 60 random locations throughout the Dresden Reach in fall, 2013–2014, and 30 sites from the Starved Rock Reach in fall 2014. Seeds were removed from sediment samples, identified to the lowest possible taxonomic level, weighed to nearest 0.1 mg, were used to estimate the overall seed density (kg/ha; dry mass) and were assigned appropriate total metabolizable energy (TME) values to calculate duck energy days (DEDs). All sampling locations (i.e., river reaches and backwaters) had low average density (<175 kg/ha) of seeds and tubers and low duck energy day estimates (<1,200 DED/ha) when compared to managed wetlands. In river reaches, the Dresden reach had the greatest ECC in 2014 (109.0 ± 85.7 kg/ha; n = 30), followed by Dresden Reach in 2013 (47.2 ± 10.7 kg/ha; n = 28), and Starved Rock Reach in 2014 (13.7 ± 35.7 kg/ha; n = 30). Energetic carrying capacity in backwaters was also low (53.0 ± 13.7 kg/ha; n = 20). Upper Illinois River ECC estimates were -88.5 % to -94% below estimates from lower Illinois River valley wetlands, and were below waterfowl foraging giving-up density (GUD) estimates prior to peak fall migration. The Des Plaines River exhibited greater ECC estimates (95.8 ± 64.2 kg/ha; n = 40) than the Kankakee River (37.7 ± 14.0; n = 18), despite abundant commercial barge traffic and channel manipulation in the Des Plaines River. Additionally, Mallards collected from public and private hunting areas on the Illinois and Des Plaines rivers fed primarily on agricultural seeds, and low food availability coupled with significant disturbance from hunting, recreational and commercial barge traffic may limit the value of the Upper Illinois River for waterfowl. Conservation planners should consider integration of waterfowl management areas which utilize and encourage growth of remnant naturally-occurring aquatic vegetation and incorporate moist-soil management practices and water level manipulation to maximize the potential for quality waterfowl habitat the Upper Illinois River.