Help for the Prairie State Wetland's Birds: Built habitats might keep them viable

Apr 1, 2001

Black-crowned night heron
Credit Joe Milosevich

Illinois' best hope of protecting its endangered wetland birds may be to shore up their natural habitats.

Each spring, herons, egrets, blackbirds and terns migrate to this state's wetlands to mate, nest and breed. But these ecosystems, so rich in bird life, also are the most threatened, says Steve Bailey of the Illinois Natural History Survey. In fact, 90 percent of this state's original wetlands are gone. As a result, such species as the black and yellow-crowned night herons and the snowy egret are declining in Illinois.

These large birds like to nest in groups, which means they need ample territory to forage and feed their young. Consequently, they establish colonies, or rookeries, in wetlands that can ensure plentiful feeding. The shrinkage of the wetland habitats puts pressure on the rookeries and their inhabitants.

Until the early 1900s, the Illinois and Mississippi rivers supported enormous rookeries that birds returned to each spring. But the wetlands, and the birds, have been displaced by factories, farms and residential areas.

The depletion of these wetlands, and the resulting degradation of rookeries, has forced birds to nest in marginal locations that offer too little protection from predators.

Ironically, Illinois' largest remaining rookery and black-crowned night heron colony is located in an urban area, in Alorton on a narrow strip of woods wedged between an abandoned railroad and an East St. Louis housing development. Located 1.5 miles from the Mississippi, Alorton has lakes and bottomlands enough to support the breeding activities of five species of wetland birds. Last year, 800 nesting pairs of black-crowned herons were counted at Alorton among more than 2,000 migrants, including little blue herons, cattle egrets, great egrets and snowy egrets.

The other remaining large rookeries are located in the Chicago area: Lake Renwick in Plainfield, Baker's Lake in Barrington and Lake Calumet on Chicago's South Side, where, until 1996, three marshes offered habitats for up to 900 nesting pairs of black-crowned herons. Overcrowding is thought to have driven many of the pairs out. When the birds were forced to relocate, some ended up in natural areas such as McGinnis Slough in the southwest suburbs, but others ended up at the steel mill graveyards of Gary, Ind.

Fortunately, some enterprising environmentalists and governmental agencies have taken matters into their own hands and reinforced some of the rookery sites in Illinois.

In 1999, the voters of the Forest Preserve District of Will County approved a $70 million tax increase that included spending $450,000 to reinforce habitats at the Lake Renwick Heron Rookery. Workers built new nesting platforms and replanted depleted vegetation to prevent soil erosion around the rookery's seven islands. The project also calls for lining the shores with rocks to prevent soil erosion and bordering brush with logs to avoid depletion through wave action.

The designers aimed to replicate the eroded base of the rookery in hopes that the colony's natural ecology will redevelop. Icy conditions slowed these efforts, but the project was scheduled for completion in mid-March, in time for the birds' breeding activities.

After last year's rookery restoration work at Baker's Lake Nature Preserve in Barrington, the number of nesting pairs there climbed from 200 to 315. As a result of the combined efforts of the Cook County Forest Preserve District, the Illinois Department of Natural Resources, the Illinois Nature Preserves Commission and Citizens for Conservation, eight black-crowned nests were counted. There were none in 1999.

Nesting material at Baker's Lake includes telephone poles and Christmas trees. Because black-crowneds tend to select lower level nest sites, 350 Christmas trees were strewn at the restored Baker's Lake rookery. The recycled trees opened new nesting possibilities for the endangered birds.

Meanwhile, the tendency to select low nest sites, including reeds and tall grasses, has made Lake Calumet, with its plentiful reeds and cattails, an area favorable to the black-crowned night herons but undesirable to higher-dwelling great blue herons and cormorants.

Some argue that erecting artificial structures might discourage birds from seeking suitable natural habitats elsewhere. But others contend that if humans don't get involved in habitat construction where birds are endangered, the conditions that force those birds into marginal nesting areas will worsen.

There's evidence to support the latter view.

For example, the 1999 flooding of Big Marsh at Lake Calumet killed vegetation and forced black-crowned night herons to relocate to a smaller marsh. And when great blue herons, great egrets and double crested cormorants outnumbered black-crowneds at Baker's Lake, they took the best nest sites, which forced the night herons to seek shelter elsewhere. The number of black-crowned pairs dropped from a high of 228 in 1988 to just 11 in 1992. Indeed, black-crowneds are showing up in such marginal nesting areas as the site of the defunct Johns Manville asbestos plant in Lake County, says Brad Semel, district natural heritage biologist with the Illinois Department of Natural Resources. Thus, while preserving and restoring natural habitat is the ideal solution for staving off the destruction of a species, it isn't always an option.

Having to change breeding locales every two to three years is stressful to the birds, which cuts down on breeding productivity. Birds maintain their numbers not necessarily because their habitat remains the same, but because it provides protection from predators and resembles the original. Furthermore, it can be argued that the loss of a single nesting location could leave hundreds of pairs stranded. Consequently, leaving the birds to their own devices may actually imperil them.

Creating support structures and controlling water levels to protect vegetation could keep the birds out of marginally viable nesting areas in Illinois and other states where habitat is scarce. Therefore, efforts such as those at Baker's Lake and Lake Renwick by natural resource managers, environmental groups and resident volunteers are to be lauded. They may be our last hope to save breeding wetland birds. 

Writer and consultant Gail Goldberger is editor of the Chicago Audubon Society's COMPASS.