A prothonotary warbler rests on a branch. Photo by Melissa McMasters from Memphis, TN, United States, CC BY 2.0, via Wikimedia Commons.

May 1, 2024

The Lower Mississippi River Bottomlands Natural Division: A Land of Rare and Unusual Animals

A purple map of the state of Illinois with a zoomed in area in the south west corner of the state indicating the Lower Mississippi River Bottomlands Natural Division.
A map of the Lower Mississippi River Bottomlands Natural Division. Map courtesy of Sarah Marjanovic.

Part 1 of this series highlighted sites where visitors can experience the diverse and unique habitats and plants of southwestern Illinois’ Lower Mississippi River Bottomlands Natural Division. Let’s now discover some of the rare reptiles, amphibians, birds, mammals and fishes that reside within bald-cypress-tupelo gum swamps, floodplain bottomland habitat and a silt-laden shallow regions of the Mississippi River.

Swamps and Sloughs Host Distinct Reptiles and Amphibians

Among the unique herpetofauna inhabiting the area are green treefrogs, northern cottonmouths and mole salamanders. All three of these species share a similar range within the southernmost seven counties of Illinois and a similar preference for low woodland, swamp and flatwood slough habitats.

Sitting open-mouthed on the bottom of a river, oxbow lake or cypress swamp, the Illinois-endangered alligator snapping turtle wiggles a pink ‘lure’ extending from its mouth to attract its fish prey. It is the largest freshwater turtle in North America, weighing between 35 and 150 pounds.

Another resident of cypress-tupelo swamps and river sloughs, the state-threatened non-venomous Mississippi green watersnake is a stout, greenish black or olive brown snake. Its range is restricted to extreme southwest Illinois, which is the northern most range for this snake species.

A photo collage of a black and dark green water snake on dry ground, a green tree frog on a branch, and a dark brown snake on top of leaf litter and gravel with its mouth open. There is text overlaying each image. The text to the left is Mississippi green water snake, Nerodia cyclopion. The text in the middle is green tree frog, Hyla cinerea. The text to the right is northern cottonmouth, Agkistrodon piscivorus.
Photos by Scott Ballard.

Illinois’ Mississippi River Floodplain Provides Ecologically Important Bird Habitat

The website eBird notes that 228 species have been sighted at Horseshoe Lake State Fish and Wildlife Area, with 212 species noted at LaRue-Pine Hills Ecological Area. Both Horseshoe Lake and LaRue Pine Hills are recognized as National Audubon Society Important Bird Areas.

Notable species such as the red-shouldered hawk, state-endangered northern harrier, state-threatened least bittern, state-threatened common gallinule, prothonotary warbler, fish crow and bald eagle may be sighted in the area. Wetlands in the region provide essential waterfowl refuge habitat, as well as high-quality habitat for shorebirds, wading birds and neotropical migratory songbirds.

Swamps and Marshes Host Mammals

A brown rat with a long tail sits near and on some tan grasses.
Marsh rice rat, Oryzomys palustris. Photo by Sturgis McKeever, Georgia Southern University, Bugwood.org.

Within the Lower Mississippi River Bottomlands Natural Division live two mammals species whose names suggest their habitat—the swamp rabbit and marsh rice rat.

The swamp rabbits found in Illinois are at the northern edge of their range and occur in isolated patches of optimal habitat. Swamp rabbits live in areas close to water and are adept swimmers. To avoid predators, swamp rabbits will take to the water, often disappearing from sight by diving under overhanging vegetation or roots. Locating swamp rabbits often entails locating the elevated sites where they rest or defecate.

Adaptations on the feet of the semi-aquatic marsh rice rat allow it to live in swamps and marshes. Often, this 8-inch-long rodent will dive underwater to escape predation. Although more common in marshlands in the southeastern section of the United States, the state-threatened marsh rice rats can be found in the southern one-fourth of Illinois.

Unique Aquatic Communities Host Exceptional Fishes

According to Brian Metzke, an Aquatic Ecologist in the Illinois Department of Natural Resources’ Division of Natural Heritage, rare assemblages of native fishes are present in the waters of the Lower Mississippi River Bottomlands Natural Division.

“In the Mississippi River are fishes such as the sturgeon chub, sicklefin chub and crystal darter that inhabit areas with fine substrates in low gradient, slow-moving and turbid waters of the Mississippi River,” he explained. “Equally interesting are the bantam and redspotted sunfishes that inhabit densely vegetated backwater and swamp communities.”

According to An Atlas of Illinois Fishes: 150 Years of Change, published in 2022 by the University of Illinois Press, the state-endangered sturgeon chub is known only from the southernmost section of the Mississippi River. Adult sturgeon chubs may be up to 3.25 inches in length. Adult sicklefin chubs are about an inch longer and are more common than sturgeon chubs. Sicklefin chubs are often collected in concert with the sturgeon chub.

“Another unique fish in the division is the crystal darter, which is found in flowing, moderately deep waters and today is most prominently found in Illinois within the lower reaches of the Mississippi River,” Metzke said. “When disturbed, crystal darters will bury themselves in the mixed sand and gravel substrates they prefer.”

The dense aquatic vegetation found in swamp and oxbow communities holds equally interesting fish species.

Bantam sunfish are found often in Louisiana and parts of Texas, Arkansas, Kentucky and Tennessee, yet this Illinois threatened species inhabits LaRue Swamp in areas with heavy vegetation, stumps and logs in sloughs, oxbow lakes, ponds, backwaters and swamps.

The redspotted sunfish pictured above right is so named for the rows of bright red-orange speckles along its sides. In Illinois, redspotted sunfish occur in scattered locations along the Wabash, Ohio and Mississippi rivers and in tributaries of the Sangamon River. Their preferred habitats are ponds, lakes, pools of creeks and small to medium rivers, and swamps having dense vegetation.

Point your vehicle toward southwestern Illinois today and you will find locations that harken to soggy landscapes reminiscent of swamps of the South that hold a gleam of promise as home to an amazing diversity of plants and animals.

Kathy Andrews Wright is retired from the Illinois Department of Natural Resources where she was editor of Outdoor Illinois magazine. She is currently the editor of OutdoorIllinois Journal.

Share and enjoy!

Submit a question for the author