Birds that nest in marshes are the least understood birds in Missouri. One reason for this is the difficulty of entering marshes, especially in summer. We know even less about other marsh inhabitants or the intricate relationships that play out within these lush, aquatic systems.
Of Missouri's natural communities, marshes are the richest. Compared to upland grasslands and forests, marshes in summer produce the most animal biomass per unit area in the least amount of time. They also provide the greatest number and assortment of niches for wildlife. Marshes could be called "nature's cities" because their abundant resources allow their residents to pack densely together.
Marshes are low-lying tracts of land that hold water throughout much of the year. They are dominated by rooted, perennial, non-woody vegetation that emerges above the water's surface. Marshes support perennial, water-loving plants, such as bulrushes, spike rushes, arrowheads, burreeds, cattails, water lilies and pickerel weed. Many of these plants provide marsh birds with nesting habitat and cover. The presence of water during much of the year protects eggs and nestlings from land-dwelling predators.
In Missouri, marshes were once common in our river floodplains, especially along parts of the Missouri and Mississippi rivers. Under natural conditions, new marshes are always forming while others are silting in. In the last century, however, Missouri has lost as much as 90 percent of its wetlands. Modern control of our big rivers prevents new marshes from forming, and existing marshes have been drained at an accelerated rate.
To obtain more information about marsh birds, Missouri Department of Conservation biologists periodically coordinate surveys of selected marshes with ornithologists, conservation area managers, U.S. Fish and Wildlife Service biologists and interested citizens. These marsh bird surveys began in the early 1980s and are conducted semi-annually.
The surveys begin by playing taped calls to provoke birds to respond. Some species answer the tapes more readily than others. Some are more likely to call after dark, and others are unlikely to answer at all. To pinpoint respondents and locate non-callers, surveyors walk parallel courses in patterns that allow them to cover much of the marsh. They record the number of nests they locate, including the species using them, the number of eggs or young, the water depth and the type of vegetation supporting the nest.
Typically, surveyors target about two dozen marshes during the May-through-June survey period. Most of the marshes are on Conservation Department areas and national wildlife refuges. Most are located in western and northern Missouri. Often, floods or droughts interfere with surveys, but researchers survey as many as they can.
Missouri's Marsh Nesters
Not only are marshes fascinating, they are also important to the survival of many specialized species. Of Missouri's 20 rarest breeding bird species, nearly half nest in marshes. Marsh birds vary in abundance, from the widespread least bittern to the seldom-seen black rail. We've listed some of the birds that inhabit Missouri marshes.
Pied-billed grebe: This nine-inch swimmer has a black bar on its bill. Its courtship call is similar to that of a loon and is often heard at night. Pied-billed grebes build soggy, floating nests anchored on rooted vegetation in water one- to two-feet deep, and they lay up to 10 eggs per clutch. The young sometimes ride on their parents' backs.
In his 1907 book, "A Preliminary Catalog of the Birds in Missouri," Otto Widmann referred to pied-billed grebes as common. They are rarely reported now, but good populations remain at Ted Shanks Conservation Area (Pike County) and Grand Pass Conservation Area (Saline County).
American bittern: Standing two-feet tall, these wading birds tend to hide in reeds, often with their bills pointed skyward to match the vertical, surrounding vegetation. Their call is a low, pumping sound that can carry for a mile. They often nest alone on small islands surrounded by thick, emergent vegetation. They lay four to five eggs.
According to Widmann, American bitterns were once common residents here in the summer, but now less than a dozen individuals are found each year. Ted Shanks Conservation Area is the most dependable site.
Least bittern: Only 11-inches tall, least bitterns are the smallest members of the heron order in Missouri. They readily emit their "coo-coo-coo" calls and are fairly easy to locate wherever they occur. They nest over water in the densest patches of vegetation, raising broods of four to five young twice each year.
Widmann called the least bittern, "A denizen of the reedy lakes and sloughs in the flood plains of the Mississippi and Missouri rivers." Today, about half of the marshes surveyed harbor least bitterns.
Sora: Our most common rail, these seven-inch, charcoal-colored birds are difficult to locate because of the dense marsh vegetation they inhabit. They are easiest to find in May by their chirping call that descends in pitch and volume. The nests they weave into vegetation over water are nearly impossible to locate. They lay as many as 12 eggs per clutch.
Though perhaps a regular breeder in many Missouri marshes, soras are seldom found. This apparently was true in Widmann's era, too, because he wrote little about their nesting status. Soras are much more common during migration and can be legally hunted.
King rail: These 14-inch rails are listed as endangered in Missouri. Where present, they are relatively easy to detect by surveyors because they readily answer to electronic playbacks of their calls. Later in the summer, they bring their broods out of the reeds to feed on open mud flats. Nests are canopied, basket-like structures suspended in vegetation over water, often near shore.
In Widmann's day, king rails were, in his words, "A fairly common summer resident in the marshes along the large rivers." Now, only one or two Missouri wetlands are known to harbor king rails.
Common moorhen: The primary difference between these 11-inch, dark gray swimmers and American coots is their red bill and face-shield. They are easy to find because they select marshes with open water and are often seen swimming in rafts, sometimes with their broods in tow. They suspend their nests in vegetation, often right at water level, and they lay clutches of up to 15 eggs. As water levels fall during their nesting period, they build ramps to their nests.
In 1907, according to Widmann, common moorhens occurred in the bottomlands from St. Louis northward. Currently they are known to live in fewer than a half-dozen Missouri wetlands.
Marsh wren: Of the six wren species that occur in Missouri, the marsh wren is most closely tied to marsh habitat. They can be identified by their cocked tail, russet color and white line through the eye. Their call, a wren-like chatter, often resonates from deep within a marsh. They associate with tall sedges, rushes and grasses. Their nests are softball-size globes intertwined with supporting vegetation, with entrance holes in the side. They nest twice per nesting season and lay an average of five eggs.
Widmann called marsh wrens "fairly common summer residents in the marshes of the Mississippi and Missouri floodplains and locally common in the prairie regions of the north and west." They are still commonly found where dense marsh vegetation occurs over shallow water.
Yellow-headed blackbird: Along with red-winged blackbirds, these are the most easily seen and identified marsh birds. Males emit raspy, buzzy calls to defend territories, and one male may attract several females to mate with him. Nests are invariably constructed over water, often in cattails. They lay three to five eggs and nest twice each year.
In Widmann's day, yellow-headed blackbirds were found west of a line from the northeastern to the southwestern corners of the state. Today, they nest only in northwestern counties and are limited to no more than five to 10 Missouri marshes.
Other birds that use Missouri marshes for nesting are the mallard, blue-winged teal, black-crowned night-heron, American coot, sedge wren, common yellowthroat, swamp sparrow and great-tailed grackle.
Somewhat rarer marsh birds include Wilson's phalarope and black tern. The latter was formerly a common breeder. It was last known to nest at what is now the Marais Temps Clair Conservation Area (St. Charles Co.) in the 1950s. The black rail is one of the rarest marsh birds in the country. Although Missouri lies in the center of its Midwestern breeding range, it has been detected less than half a dozen times during the state's history.