Evaluating Habitat Dynamics for Lesser Scaup on Pools 13 and 19 of the Mississippi River

The lesser scaup (Aythya affinis) is a diving duck that migrates through Illinois following the Mississippi Flyway. The scaup population began to decline in the mid-1980s, and numbers have not returned to what they were before this drop. One theory to explain this decline and the lack of recovery suggests that a decrease in food quantity and quality at migration stopover sites may be the cause. If female scaup are unable to forage nutritionally dense foods, they may arrive in the breeding grounds with fewer fat reserves and lay fewer eggs.

Under a Federal Aid in Wildlife Restoration (W-200-R-1: Waterfowl and Large River Ecology) grant, personnel from Western Illinois University and Illinois Natural History Survey Forbes Biological Station collaborated with U.S. Fish and Wildlife Service and U.S. Geological Survey biologists to evaluate current food availability at key stopover areas along the Mississippi River (Pool 13 and Pool 19). The 2019 and 2020 scaup food sampling effort revealed that fingernail clams and snails are some of the most abundant foods in these areas. Also collected were historical aerial waterfowl inventory, hydrology and aquatic vegetation data which were used to better understand how the environmental conditions in these areas have changed over the past four decades. Our methods for quantifying vegetation coverage utilized Landsat imagery, making it possible for biologists to analyze coverage quickly and remotely in future years.

A secondary part of this research involved conducting controlled feeding trials with wild-caught scaup to see how they metabolize some common foods. Understanding the amount of energy derived from these foods may help prioritize conservation actions as well as explain the effect of landscape-level change on population dynamics. We measured True Metabolizable Energy (TME) of amphipods (Gammarus spp.), planorbid snails (Planorbidae), fingernail clams (Sphaeriidae), wild millet (Echinochloa crus-galli) and chironomid larvae (Chironomus spp.). Any excreta (waste matter) the scaup produced after being fed was collected with a bag strapped to each bird with a body harness (Figure 2). Average TME (kcal/g[dry]) was greatest for wild millet (2.2), followed by chironomids (1.81), amphipods (1.33), planorbid snails (0.17), and fingernail clams (-0.59). These are the first TME estimates that have been calculated for scaup. They were used to estimate current energetic carrying capacity in our study areas and will also be used to improve the accuracy of future food resource evaluations.

Our carrying capacity estimates suggested that both study areas contained enough food to support the numbers of scaup that stopped there in 2019 and 2020. River conditions can, however, change rapidly. The average yearly discharge of water from both dams has gradually increased over the last four decades, along with the number of days each Pool has spent at or above minor flood stage in the spring. As larger amounts of water move though these Pools there is an increase in suspended sediment. This sediment limits the amount of sunlight that reaches submersed aquatic plants and affects macroinvertebrates that may not be as abundant as fingernail clams or planorbid snails but are more nutritionally dense.

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Lauren Larson is originally from Owatonna, Minnesota. She graduated with a bachelor’s in Biology from Wartburg College in 2016 and earned her master’s from Western Illinois University in 2021. She currently works for the U.S. Fish and Wildlife Service, focusing on wetland conservation projects and endangered species recovery.