Established in 1958, the Mark Twain National Wildlife Refuge Complex encompasses 345 miles of the Mississippi River and includes 45,000 acres.The Long Island Division is one of the original Mark Twain National Wildlife Refuge units, and is located six miles north of Quincy, Illinois in Pool 21, in the south-central part of the state. This 6,300-acre division consists of a complex of islands, sloughs, ponds and bottomland forests.
This entire Mark Twain complex historically consisted of the Mississippi River and its changing system of sloughs, islands and sandbars. Annual floods changed the course of the river, and created new wetlands, deposited nutrient-rich sediments on forests and prairies and provided spawning habitat for fish. As European settlers arrived in the 19th century, large tracts of floodplain forest and prairie were lost to agriculture and other development. The Mississippi River became an increasingly important travel and trade route so Congress authorized a series of navigation improvements to be implemented by the Corps of Engineers. In 1930, construction began on a series of locks and dams to provide a 9-foot-deep navigation channel for heavy barge traffic. These dams created a series of 26 navigation pools extending from St. Paul, Minnesota to St. Louis, Missouri. The Corps was also given flood control responsibilities, and assisted landowners in building levees that isolated the river from its historic floodplain except during extremely high floods.
These human-caused changes to the Upper Mississippi River have dramatically impacted wildlife habitat. Over time, sediment from soil erosion has been filling wetlands, reducing water clarity and destroying habitat. Increased water levels in the pools formed by the dams have accelerated island erosion and reduced the diversity of bottomland forests. Many efforts are now underway to strike a better balance between the needs of humans and wildlife.
Migratory waterfowl, raptors, shorebirds and songbirds use the tremendous food resources provided by the bottomland forest, sloughs, wetlands and rivers in the Long Island Unit of the Mark Twain National Wildlife Refuge.
In March and April, some 26 species of migratory waterfowl can be found here. These include Green-winged Teal, Redhead, Red-breasted Merganser, Hooded Merganser, Northern Pintail and Wood Duck.
During spring when water levels are very low, many of the shallow bays and sloughs form mudflats which provide temporary habitat for shorebirds such as Semipalmated Plover, Greater and Lesser Yellowlegs, White-rumped Sandpiper, Dunlin, Stilt Sandpiper, both species of dowitchers and Common Snipe.
In summer, wading birds breed here, including Yellow-crowned Night-Heron.
Many neotropical migrants choose this region in which to breed. These include Yellow-throated and Prothonotary Warblers. In addition, this is possibly one of the best areas in Illinois for breeding Brown Creeper.
In a typical year, at least 180 species of birds visit the refuge with at least 80 of them breeding.
This site was chosen as an IBA because it met the criteria for Wading Birds, Shorebirds, and Waterfowl.