Rivers of Illinois: Ecology: Animals
By Micah Moen
Rivers of Illinois: Mississippi, Illinois, Wabash and Ohio Ecology: Animals Ecology is the scientific study of relations that organisms have with each other and their natural environment. In this podcast, we will focus on some of the river-dependent animal species of Illinois. The diverse animal life of these rivers is among the richest of the world’s temperate-climate river systems. Invertebrates An invertebrate is an animal without a backbone. This group includes worms, mollusks, crustaceans and insects. They exhibit a variety of adaptations for surviving in the constantly changing conditions of the large rivers. While many invertebrates live on the river bottom, others live on the water’s surface and shores. Earthworms have a segmented body and a true body cavity. Some earthworms are entirely aquatic while others live along rivers, burrowing in the mud. . They feed on dead animals, plant material and other organic substances. Leeches have a flat, segmented body with a sucker at each end of the body for attachment to objects. They live in water or other moist habitats. Many leech species are external parasites that suck blood from animals to survive, but others are scavengers or predators. Parasitic leeches make small cuts on their host and exude a pain killer and a substance that keeps blood from clotting so that they can feed without being noticed. Leeches are two to three inches long and swim with an inchworm-type movement. The six-spotted fishing spider can be found on shore, on underwater plants or on the surface of the water. It can walk under water as it climbs down a submerged plant leaf or stem, glide across the water’s surface being pushed by the wind or dive holding an air bubble in its legs to breathe from. It can remain under water for about 30 minutes. Fishing spiders eat mostly insects, but they will also take small fishes, frogs or tadpoles, if available. Freshwater sponges have no true tissues or organs. They grow attached to objects on the river bottom and have a tough outer skin with tiny pores through which water flows. The size, shape and color vary, but in the Mississippi River most sponges look like brown algal growths on submerged objects. They filter microscopic food particles, like bacteria and algae, from the water. Freshwater sponges make important habitats for other organisms. Freshwater shrimp have five pairs of legs, the first having grasping claws. They are more common in southern Illinois than the rest of the state and live for about a year. They live in slow-moving backwaters in areas with plenty of vegetation. These invertebrates have a flattened abdomen and eat living and dead plants and small animals. The species commonly found in Illinois is the Mississippi grass shrimp. Snails, mollusks with coiled shells, often live near and in the large rivers of Illinois. They feed on algae, rotting wood, fungi, bark and plants. An example is the striped whitelip snail that lives on river banks and near swamps. Many mussels live in rivers and streams in Illinois. Like snails, mussels are mollusks. They have two hinged halves to their shell that they can open and close with internal muscles. Inside the shell is a large organ called a foot that is used to pull the animal along the bottom, on which it lies partially buried. Mussels continually pump water through their bodies to obtain oxygen and food that normally consists of plankton and other tiny free-floating organisms. The threeridge mussel is the most common mussel in the Illinois River. It has three prominent ridges on the thick shell’s outer surface that give it its name. The threehorn wartyback is a small, rounded mussel. It has three large protrusions on its shell. These mussels are yellow-brown or green when they are young and turn dark brown as they get older. Crayfish have large, bumpy claws and live in areas of vegetation, which they eat. They often burrow in muddy river banks and wetlands. The virile crayfish (Faxonius virillis) is the most common in Illinois although it is not found in the Wabash or Ohio rivers. Insects The rivers are also home to many insects. Insects can be found living in and on water and have adaptations like external gills for breathing and a streamlined body for moving quickly in the water. Predaceous diving beetles carry an air supply trapped under their wings when they dive under water. To swim they move their legs in unison and surface for air tail first to refill their supply. Diving beetles are very aggressive and cannibalistic. They eat worms, dragonfly nymphs, snails, tadpoles and sometimes fishes as big as themselves. Even their larvae can puncture prey and suck out their fluids. Many other insects lay their eggs in the water. After the eggs hatch, the immature forms live in the water until they change into the adult stage. For example, most of a dragonfly’s life is spent as a nymph. Dragonfly nymphs are aquatic and have gills inside their body. They eat other insects, mollusks and worms. Mayflies live on or in the substrate of a water body during their nymph stage, feeding on plants and dead organisms. When they transform to the sub-adult stage, they may float to the surface and shed their skin, sometimes floating on the shed skin for a while. At this time, they are easy prey for fishes and other animals. The sub-adult soon changes to the adult form. Adult mayflies do not feed and generally live for a few hours to a few days. The water strider lives on the surface film of rivers. It can skate across the water’s surface because of water-repellent wax on its feet. It also uses the feet to sense vibrations to locate prey and a mate. The dragonfly adult lives near the water where it began its development. Adult dragonflies flap their wings alternately, allowing them to hover as well as fly backwards. They can fly at speeds up to 75 miles per hour and are voracious predators. Deer flies may live near water. They drop their eggs on vegetation above water, and their larvae drop into the water when they hatch. Many deer fly larvae live in mud. Adult deer flies feed on liquid food: females eat blood, while males drink flower nectar. Fishes Many fishes have special traits that help them to survive in the large rivers that often contain high sediment levels, fast velocities, human interferences and pollution. For example, some fishes, including catfishes and carp, have adapted to survive on low oxygen levels when dissolved oxygen levels drop in rivers due to too much sediment, high temperatures, low flow and/or little shoreline vegetation. Other fishes utilize the pools made by dams or backwater lakes to spawn. Unlike most fishes, catfishes do not have scales. They do have eight, whiskerlike barbels around their mouth to help them find food. Sharp spines on the back and shoulder fins are used for protection. The flathead catfish is active at night and unlike other catfishes, only eats live fishes. The channel catfish feeds on the bottom, eating insects, fishes and plants and has a deeply forked tail. White bass travel in large schools and chase bait fish in the open waters close to the surface. These yellow-eyed fish can often be found in large numbers below dams and other obstructions in the water where they like to spawn. The shortnose gar has a snout that is half the length of its head. The body is covered with diamond-shaped scales. This species lives near aquatic plants and submerged logs and can live for about 20 years. The shortnose gar eats crayfish, perch, sunfish, mayflies and carp. The black crappie prefers clear water that moves slowly. These These fish hide in groups around submerged objects in the water, often at depths of 15 feet or more. The black crappie eats insects, plankton, larvae and small fishes. River shiners are common minnows found only in large rivers. They live in the main stream of water and along the banks. These fish eat mostly insects, algae and plant matter. River darters are different from many other fishes in that they do not have an internal swim bladder to help them maintain their place in the water column, so they sink to the bottom when they stop swimming. They can be found in deep chutes and riffles where there is a swift current. River darters commonly eat small
crustaceans, snails and insect larvae. Gizzard shad are often used as bait by fishermen. They live in open water near the surface and collect food, like microscopic plants and animals, with their gill rakers. They are an important food source for many other fish species. The freshwater drum has a humped-back appearance and lives near the river bottom. It gets its name from its ability to make a drumming noise with its swim bladder. These fish normally eat insect larvae, crustaceans, fishes, clams and snails. The bigmouth buffalo eats what it strains from the water with its gill rakers, including plankton and aquatic beetles. This fish has a large head with a sucker-type mouth and lives in schools. Common carp are invasive species that can adapt easily to nearly all river conditions. They are bottom feeders that eat vegetation, insect larvae and small crustaceans. Carp can out-compete many other species and may grow to be more than 80 pounds in weight. Sauger live in loose groups near the bottom and are active at night. This fish closely resembles the walleye except that is it smaller. It is a predator, usually feeding on fishes and insects. Amphibians Amphibians have moist skin that allows for breathing, so they must live in or near water. Many species have their eyes near the top of their head so that they can see above water while most of the body remains in the water. Even if an amphibian lives mainly on land, it must return to water to lay its eggs. Salamanders are very slimy and usually active at night. . In the rivers of Illinois, salamanders tend to live under flat rocks and eat fishes, insects and mollusks. The hellbender lives in the Wabash and Ohio rivers. It likes fast-running water and has a flattened head and a thick body. These salamanders eat insects, crustaceans, earthworms, fishes and even their own eggs. This species is endangered in Illinois, mainly due to siltation of the rocky substrate that it needs. The mudpuppy can be found statewide. It keeps its bushy external gills all its life and has four toes on each foot, different than most salamanders which have five. Mudpuppy salamanders were named from the mistaken belief that they bark. Bullfrogs live on the rivers’ edges and defend a territory from other bullfrogs. A bullfrog’s eardrum is wider than its eye. These frogs live alone and eat almost anything they can catch and swallow. The cricket frog also lives on the edges of water bodies. This frog has warty skin and is usually active during the day. Cricket frogs are in the treefrog family but do not live in trees. They feed on spiders, mites and insects. reptiles Many types of reptiles have traits that make them well-suited for aquatic environments. Aquatic turtles have webbed feet to help them swim, and many can retreat into their shell for protection from predators. Snakes are streamlined for swimming and hiding in small crevices. Even if the adult is entirely aquatic, all reptiles must go to land to lay their eggs. Spiny softshell turtles live in river sections where the bottom is sandy. Their tan, leathery shell is covered with bumps. This animal likes to bury itself in sand with only its head sticking out of the water to breathe. Softshell turtles eat fishes, crustaceans, insects, amphibians and mollusks. The snapping turtle has a huge head and a long tail with a saw-toothed upper surface. It spends much of its time on the bottom of rivers waiting for its prey of insects, fishes, amphibians, birds, reptiles and vegetation. Painted turtles have a red, yellow and black pattern on their smooth shell. They prefer to stay in shallow, muddy water. Although they are aquatic, they can also be found basking on land, logs or rocks on the shore. A variety of snake species live in the rivers feeding on fishes and amphibians. Most are active in the day except for hot periods in summer when they become active at night. They swim in the water and bask on rocks in the sun. Some of these snakes include the diamondback water snake, plainbelly water snake (Nerodia erythrogaster) and northern water snake (Nerodia sipedon). Birds While some birds are generalists and can survive in a wide variety of habitats, birds that live near or float on the water have special adaptations. For instance, some birds, like the herons, have a long, skinny neck for plunging into the water. Others have a sharp beak for spearing fishes, water-resistant feathers to help them float or webbed feet for paddling. The bald eagle is the national bird of the United States and is the only eagle found exclusively in North America. These birds make a nest that is on average five feet wide and three feet deep. A bald eagle can live to be more than 30 years old. Bald eagles live near open water where they can find abundant food sources and old growth trees for nesting. The great blue heron is a tall wading bird that is commonly found along the rivers’ shores. Its feet have three long toes pointing forward and one pointing backward that allow the bird to spread its weight and walk easily on mud. Fishes, insects, crayfish and other small animals, which they swallow whole, make up the diet. These birds nest 30 to 70 feet above the ground in treetop colonies. The ring-billed gull has a yellow bill with a black ring near its tip. This species migrates through Illinois. It tends to return to the same colony where it hatched to breed each summer in Canada and the northern United States. American crows are generalists. They can survive almost anywhere. They have black feathers and live in cooperative groups. They eat dead animals, grain and garbage. Turkey vultures feed on dead animals. They soar along river bluffs and nest in cliffs. These birds are large and dark with a red head and a great sense of smell. The least tern is a species that is endangered federally and in Illinois. This bird lives in Illinois only during the summer months and likes to nest on river sandbars. The double-crested cormorant perches in dead trees and riverside driftwood. It floats and dives in the water to pursue fishes. Its body type makes it an adept swimmer but less skilled flier. Wood ducks are common migrants through Illinois and summer residents. The males are brightly colored in the winter and spring, while the females are gray-brown. Several females sometimes lay eggs in the same nest.
Unlike most other waterfowl, wood ducks perch and nest in trees. The cliff swallow lives in Illinois in summer and nests in large groups. These small birds have long wings. They prefer to nest in cliffs, steep river banks or under overhangs. The belted kingfisher is a diving bird. It makes headlong dives into the water to catch small fishes to eat. These birds nest in vertical embankments where they make long tunnels in which to lay their eggs. Another diving bird is the osprey, one of the largest birds of prey in North America. It dives feet first into the water to grab fishes, the only type of food it eats. The spotted sandpiper is a shorebird that migrates through Illinois. It lives on sandy, muddy shorelines and “teeters” as it walks along searching for small invertebrates to eat. The semipalmated plover has a black bill in the winter that changes to yellow with a black tip in the summer. It is a migrant that lives on the river shoreline. When feeding, it runs a short distance and stops, repeating this process as it moves. Mammals The mammals that live in rivers have special traits to help them thrive in water. Many of them have small ears or can close their ears to keep water out, have webbed feet and have a tapered tail to aid them in swimming. Other mammals live near the rivers because of the abundance of food, water and shelter available. Beaver live in the rivers of Illinois. They can weigh up to 60 pounds and are active at night. They dig burrows with underwater entrances into river banks. They also make dome-shaped lodges of trees, limbs and sticks in backwater areas. The mink is another nocturnal mammal. It lives in burrows left by other animals or in brush piles along the rivers. It eats all types of small animals. Another mammal that is mostly active at night is the muskrat. Its thick, flat hairless tail can be almost as long as its body. It builds houses of vegetation in shallow water or burrows into river banks. White-tailed deer live in wooded areas near rivers. Males, called bucks, grow and shed antlers. Females are called does. They are most active during the hours around sunrise and sunset. White-tailed deer eat grasses, grains, nuts, mushrooms, leaves and twigs. Raccoons are known for their black-masked face and striped tail. They live in a variety of habitats as long as food, water and den sites are available. These animals will eat fishes, crayfish, mice, berries and nearly anything else they can find. The North American river otter is an excellent swimmer and diver, moving more easily in the water than out of it. It is active both during the day and at night. Otters tend to be very playful and will slide down the banks of the rivers. Our rivers with their tremendous resources are teeming with life. Whether living permanently in water, moving in and out of water, living near water or passing through in migration, hundreds of animal species depend on the river systems for their existence.