Two Rivers National Wildlife Refuge

Considering the life history of our priority species and the effects of human alteration of lands surrounding Two Rivers, we manage habitat using a variety of techniques and evaluate our efforts by conducing wildlife and vegetation surveys.

Habitat History

The installation of locks and dams in the Mississippi and Illinois rivers during the mid-1900’s made commercial shipment of goods possible by minimizing major water level fluctuations that historically made navigating these rivers virtually impossible. The influx of boat traffic along the rivers resulted in urban centers like St. Louis just 20 miles south of the confluence of the Illinois and Mississippi rivers and 6 miles from the confluence of the Missouri and Mississippi rivers. Water levels in these rivers can now be controlled with the locks and dams, with the stretch of river between two locks and dams named after the lock and dam on its downstream border.

But none of this could have been accomplished without consequence, the plants and animals in the floodplains of these major rivers were accustomed and even adapted to the water level fluctuations the locks and dams set to control. Historically, the floodplain had a wet-dry cycle where water levels rose in early spring and retreated in late spring which allowed areas to dry out during summer when vegetation flourished before the area was again flooded with water in fall. Highly productive vegetated areas in summer provided food for migrating waterfowl once flooded in fall, flooded backwaters in spring served as vital spawning areas for fish, and sandbar islands provided nesting habitat for terns in early summer.

Now the rivers have more stable water levels year-round. Due to the absence of major water fluctuations, water intolerant plant species could now occupy land without being drowned by annual water level rise and have crept closer to riverbanks, taking over habitat once dominated by water tolerant species that cannot compete in dry habitats.

Land managers along the Rivers have faced other challenges including pollution, the conversion of floodplain habitat to farmland, sedimentation, invasive species invasive species
An invasive species is any plant or animal that has spread or been introduced into a new area where they are, or could, cause harm to the environment, economy, or human, animal, or plant health. Their unwelcome presence can destroy ecosystems and cost millions of dollars.

Learn more about invasive species , and erosion of islands and other features within the Rivers. In addition, flood and drought events have been amplified in recent years, largely attributed to climate change climate change
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's climate system and caused change on a global scale.

Learn more about climate change .

But not all is lost, Two Rivers National Wildlife Refuge has partnered with numerous agencies and groups to restore and protect habitat for migratory birds, fish, plants, and threatened and endangered species that rely on the Mississippi and Illinois river floodplains. We have played a key role in research and monitoring and strategize with our partners on better land management and restoration techniques. We have learned to work with the new river conditions post lock and dam installation and continue to find new and innovative ways to more effectively manage habitat for the species and future generations we serve.

Habitat Management

With these major habitat alterations, the affected floodplains will never function the same. Two Rivers National Wildlife Refuge uses habitat manipulation to mimic annual wet-dry cycles that would have historically occurred along the Mississippi and Illinois rivers, for the benefit of migratory birds.

Starting in spring we pump or gravity flow water into land management units surrounded by raised berms or levees, allowing water to sit on the landscape for an extended amount of time to attract a variety of waterbirds. Migratory waterfowl and shorebirds are abundant on the refuge during this time and can be seen gathering in large numbers to feed and rest.

After a spring flood comes a dry period during summer when land management units are drained until they are dry, then disked, mowed, or burned to set back woody plant encroachment. In the absence of river alterations, floodplain succession was naturally set back by wildland fires or extended flood events of which only floodplain and fire tolerant species survived.

Following summer comes another round of flooding to attract waterbirds during their annual fall migration. The fall migration occurs in conjunction with the fall waterfowl hunting season, during which the refuge has sanctuary areas closed to public access. Sanctuary areas give waterfowl a place to feed and rest without disturbance, which can inhibit the ability of a bird to put on enough body weight to meet the demands of migration.

Waterfowl Annual Cycle

At Two Rivers National Wildlife Refuge, we manage habitat to be optimal for waterfowl (Anatidae) which include ducks, geese, and swan. Annually, most waterfowl complete a life cycle with different life events among seasons, dubbed their annual cycle.

Starting in late summer, cooling temperatures trigger waterfowl to migrate thousands of miles south from their breeding grounds in Alaska, Canada, and the northern United States, to warmer areas known as staging grounds in the central United States. Waterfowl use staging grounds to rest and feed, gearing up for the last leg of their migration south to their wintering areas, some as far as South America, in mid- to late fall. At their wintering areas, males molt into vibrant colors. They flaunt their colors with elaborate courtship displays to attract the attention of a female in the hopes of establishing a pair bond. When temperatures start to warm in spring, the couple makes a quick migration back to the breeding grounds to score the best nesting area to raise their young. During the spring sprint to the breeding grounds, waterfowl stage for shorter amounts of time in the central United States than they did the fall prior, but you can catch a glimpse of their beautiful breeding plumage at one of their short stops to Two Rivers National Wildlife Refuge where they continue courtship displays to maintain their bond. Upon arrival to their northerly breeding grounds in spring, waterfowl breed, nest, and rear their brood. By mid-summer waterfowl experience another molt to a more camouflage pattern before they once more start their journey south to the wintering grounds.

A Sanctuary for Waterfowl

In a truly spectacular feat, waterfowl can travel from the high artic to the southern coasts of the United States, Central America, and South America in a matter of weeks. Waterfowl meet the demands of migration by utilizing staging areas along their migration path where they consume calorie rich food and rest to prepare for the journey ahead. Two Rivers National Wildlife Refuge is situated along the Mississippi and Illinois rivers, a migration corridor for many species of waterfowl, where we aim to provide waterfowl the food and habitat they require during this arduous time in their annual cycle.

Part of providing waterfowl with the food and rest stops they require means closing the refuge to all public use during certain times of the year. Fall can be a particularly demanding time for migrating waterfowl due to hunting pressure and subsequent disturbance. With abundant hunting opportunities surrounding Two Rivers National Wildlife Refuge and legal requirements under the acts of which the Refuge land was purchased under, the Refuge enforces a waterfowl sanctuary period from October 16th through December 31st. During this time, we close the Swan Lake unit and all managed wetlands in the Calhoun Division to all public activities (consult the refuge hunt brochure for maps of closed areas).

Closing our most productive areas during a time of high waterfowl use means hundreds of thousands of waterfowl can feed and rest undisturbed. While these areas are off limits to up-close viewing, the Prairie Adventure Trail along the periphery of one of our closed managed wetlands has a viewing blind so you can stay hidden and still view our feathered visitors. Likewise, the Calhoun Wetland Observation Deck Trail (ADA accessible) keeps you far enough away from the ducks to avoid disturbance but close enough to see them. The viewing deck at the refuge visitor center (open year-round and ADA accessible) also offers views into several managed wetlands.

Wildlife and Vegetation Surveys

Scientists hypothesize food is likely one of the most important factors for waterfowl as they migrate between the breeding and wintering grounds. Birds that don’t accumulate enough body fat during migration may forgo breeding, courtship, or returning to the breeding grounds entirely. In order to sustain waterfowl populations waterfowl must have adequate habitat in areas used throughout their annual cycle, including staging areas like Two Rivers National Wildlife Refuge.

Waterfowl select for energy rich foods during migration including smartweed and millet seeds, and flatsedge tubers. These, along with others, are the plant species we promote through active management at Two Rivers National Wildlife Refuge that would have naturally occurred in areas that experienced a wet-dry cycle.

Biologists can estimate the number of waterfowl a wetland can support and the number of waterfowl that actually used the wetland. These estimates allow us to evaluate our management actions and inform future management decisions. In order to accomplish this, biologists annually conduct seed head surveys of common waterfowl foods in managed wetlands to estimate the total weight of waterfowl food in a wetland. Biologists also conduct waterfowl and landcover surveys in fall and spring to estimate the number of birds that use the refuge during each migration, and the total area and food available during migration.

The Refuge also works with partners to conduct fish, bat, and songbird surveys, forest inventory surveys, and aerial waterfowl surveys.