Shorebirds in the Illinois River Valley

Millions of wetland-dependent birds undergo long-distance migrations from wintering grounds in Central and South America to breeding grounds in the arctic and rely on wetlands to stop and refuel in the United States along the way. Shorebirds, which are a group of long-legged wading birds frequently found along shorelines and on mudflats, are notoriously long-distance migrants, even though individuals of some species, such as least sandpipers (Calidris minutilla), only weigh about an ounce. Refueling areas, known as “stopover sites,” are essential for migrating shorebirds to forage and replace fat stores during these energetically taxing trips. The midwestern United States is an important region that provides many of these stopover wetlands where birds stay for a few days to multiple weeks.

Shorebirds have been experiencing population declines (37 percent) since the 1970s, which can partially be attributed to loss of stopover habitat in the agriculturally dominated Midwest. Illinois in particular has experienced excessive wetland losses, but still hosts thousands of shorebirds during migration. In fact, Chautauqua National Wildlife Refuge is a Western Hemisphere Shorebird Reserve Network Site due to the abundance of birds that use the mudflats associated with this migratory bird refuge. Because of the importance of the Illinois River Valley (IRV) to migratory shorebirds, from 2016 to 2019, the staff at the University of Illinois and Illinois Natural History Survey – Frank C. Bellrose Waterfowl Research Center in partnership Illinois Department of Natural Resources and Cruce Aviation initiated aerial surveys of 95 floodplain lakes and impoundments of the IRV from near DePue to just south of Meredosia, with a goal of estimating shorebird abundance during both spring (April–May) and fall (August–September) migrations. We also wanted to estimate the area of mudflats available to shorebirds across the IRV in spring and fall, and determine if mudflat availability coincided with peak shorebird abundance.

Our results show drastically greater shorebird numbers in fall than spring (Fig. 1). Weekly survey estimates during fall averaged 22,836 (range: 4,718–83,525) shorebirds, compared to a spring average of 1,366 (range: 90–3,320). Overall abundance and mudflat availability varied by season, with more than 15 times more shorebirds and more than twice the area of mudflats available in the fall.

Our results highlight the ongoing importance of the IRV for migrating shorebirds, especially during fall migration. Wetland managers should focus on progressively exposing wetland substrates for migrating shorebirds especially during late July–August, and also in May if the Illinois River is low enough for managers to manipulate water levels. This management practice will allow shorebirds to benefit from continuous exposure of fresh mudflats, while moist-soil vegetation progressively takes over the longer-exposed mudflats and grows seeds that can be flooded for the imminent waterfowl migration from September to December.

Luke received his master’s degree from the University of Illinois in association with the Illinois Natural History Survey based out of the Forbes Biological Station in Havana, Illinois. He has been an avid hunter and fisherman his whole life and is happy doing anything outdoors with his yellow lab. Luke currently works for Solitude Lake Management in their Manassas, Virginia, office where he helps clients improve and properly maintain their lakes and wetlands.

Dr. Mike Ward is originally from Jacksonville, IL and received his PhD from the University of Illinois, Urbana-Champaign in 2004. He is currently an associate professor in the Department of Natural Resources and Environmental Sciences, in the College of Agricultural, Consumer, and Environmental Sciences at the University of Illinois and an Ornithologist at the Illinois Natural History Survey. He and his students are working on a variety of projects throughout the Midwest but also in Texas, Mexico, and Cuba. In summary, Dr. Ward studies the ecology and behavior of birds in natural and modified ecosystems in order to inform conservation and management.

Aaron P. Yetter is a Waterfowl Ecologist at the Forbes Biological Station, Illinois Natural History Survey.