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Eurasian watermilfoil |
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We were interested in submersed aquatic vegetation (SAV), which was historically widespread throughout the backwater lakes and wetlands of the Illinois River. Because of wetland destruction and degradation, SAV has been mostly eliminated from large portions of the Illinois and Mississippi Rivers. Wetland restoration projects, such as The Nature Conservancy’s Emiquon Preserve in Fulton County, have replaced a portion of historical SAV communities on the landscape, and waterfowl are using it. The INHS Forbes Biological Station found that the Emiquon Preserve made up 30 percent of waterfowl-usage days during autumn migration (2007–2013), despite accounting for only 5 percent of the flooded area in the Illinois River Valley.
SAV, such as coontail and invasive species such as Eurasian watermilfoil, grow quickly and accumulate large amounts of biomass in a single growing season. There is a potential for these species to provide a significant amount of energy for migrating waterbirds, but first we need to know how much energy birds actually digest from SAV. We caught wild mallards from wetlands in the Illinois River Valley and kept them in captivity at the Forbes Biological Station for the duration of the study. We fed six species of SAV that are common throughout the Midwest and have been documented in duck diets. We fasted each bird for 48 hours, fed a species of SAV, and collected the bird’s excreta for the following 48 hours. The results of this process, plugged into a fancy equation, give us an estimate of the amount of energy that birds assimilated from the vegetation.
Interestingly, we found that energy available to mallards within SAV species varied widely. The average across all six species was 0.68 kcal/g, compared with the average moist-soil seed which has a TME value of 1.78 kcal/g. SAV species such as Canadian waterweed (Elodea canadensis; 1.69 kcal/g) and southern naiad (Najas guadalupensis; 1.40 kcal/g) rival moist soil seed energy values. Other species, such as the Eurasian watermilfoil (Myriophyllum spicatum; -0.53 kcal/g) require more energy to digest than the bird receives from it and, therefore, may be less energetically beneficial for the bird.
Wetland restoration projects that promote SAV provide many resources for waterfowl and other water-loving creatures. SAV communities not only provide food through foliage and seeds, but also support greater populations of aquatic macroinvertebrates and fish than open water communities support. Active management, including removal of less beneficial species such as Eurasian watermilfoil, may result in greater overall wetland health and energetic value for the waterbirds that stop in for a snack on their way further south.
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