The forests, prairies and aquatic habitats of Illinois are home to over 2,500 plant species (14). Cypress Creek National Wildlife Refuge, located in southernmost Illinois, contains some of the oldest living trees east of the Mississippi River, and harbours 91 percent of Illinois’ high-quality swamp habitat (7). Leafy prairie-clover (Dalea foliosa), a highly rare and federally endangered species, exists in three locations in the United States, one of which is the Midewin National Tallgrass Prairie in north-eastern Illinois (16) (17).
Currently, there are 61 mammals native to Illinois and an additional 8 species that were historically found in the state but which have been extirpated within the last 200 years, including the American bison (Bison bison) (18). Rodents such as squirrels and rats make up the largest group of mammals and range widely in size from tiny voles to the stocky woodchuck (Marmota monax) (18). The Franklin’s ground squirrel (Spermophilus franklinii), listed as threatened in Illinois, prefers grassland habitats as opposed to wooded areas like many of its relatives, and spends 90 percent of its lifetime underground (19).
The Chautauqua Refuge found in central Illinois has been designated a ‘Globally Important Bird Area’ and accepted into the Western Hemisphere Shorebird Reserve Network (7). Up to 50 percent of the world’s canvasback ducks (Aythya valisineria) use the Upper Mississippi River National Wildlife and Fish Refuge as stopover habitat during fall migration (7). Sandhill cranes (Grus canadensis), once a common bird in Illinois, were driven from the state in the late 1890s due to the species’ very low tolerance of human disturbance. However, wetlands conservation efforts and limits on wildfowl hunting allowed the return of sandhill crane breeding populations to their historic range in Illinois almost 80 years later (20).
Reptiles and amphibians
There are 101 species of reptiles and amphibians in Illinois, 27 of which are threatened or endangered (1) (15). The largest terrestrial salamander in Illinois, the tiger salamander (Ambystoma tigrinum) is surprisingly tolerant of human disturbance, and can be found within towns and cities as long as there is access to suitable breeding ponds (15).
The alligator snapping turtle (Macrochelys temminckii), the largest freshwater turtle species on Earth, was nearly driven to extinction in Illinois but has shown signs of a rebounding population with the help of state captive breeding and reintroduction programmes (21).
Thousands of invertebrates can be found in every ecosystem in Illinois, from the federally endangered fat pocketbook mussel (Potamilus capax) that inhabits the state’s large rivers, to the Madonna Cave springtail (Pygmarrhopalites madonnensis), a tiny cave-dwelling invertebrate discovered in 2003 and named for the cave in which it was found (1) (15). The monarch butterfly (Danaus plexippus), a species with a vast habitat range and spectacular North American migration route, travels through Illinois and has been dubbed the official state insect (2).
The Upper Mississippi River National Wildlife and Fish Refuge is the longest river refuge in the continental US at 420 kilometres (261 miles), and is home to 119 species of native fish (7). Invasive aquatic species, such as Asian carp, have contributed to the list of 31 threatened and endangered fish species in Illinois (1).