Herons persist in Chicago wetlands despite exposure to banned chemicals

“So that’s the good news: Even though they’re getting an exposure, it’s not enough to cause problems – at least in those parameters we measured,” Levengood said.

The researchers did see an increase in some liver enzymes, he said, “but that’s not unexpected because the liver is trying to detoxify these compounds.” The long-term consequences of the rise in these liver enzymes are unknown, he said.

Populations of black-crowned night-herons in the Lake Calumet wetlands have fluctuated dramatically in the last 20 years, peaking at more than 1,500 birds in the early to mid-1990s. This population increase coincided with prolonged flooding in nearby rivers, which may have disadvantaged these short-legged herons, Levengood said.

Birders counted 447 black-crowns in Lake Calumet wetlands in 2005, the last year for which data are available.

Numbers of black-crowned night-herons and other colonial fish-eating birds had declined nationally – and in Illinois – by the 1960s. Many populations started to rebound after the ban on DDT. Illinois’ populations of black-crowned night-herons did not experience this comeback, however.

Many of the remaining heron colonies are found in or near industrial areas, Levengood said.

“Wetlands have persisted in these areas because they were out on the back 40 of some company and people generally didn’t have access,” he said. These urban industrialized sites provide needed habitat, Levengood said, but are also “contaminated and degraded.”

Urbanites are beginning to discover these areas, and want to clean them up for wildlife – and humans – to use, he said. Chicago’s Department of Environment is leading a drive to reclaim parts of the Lake Calumet wetlands, an effort that prompted the current study.

Editor’s note: To reach Jeff Levengood, call 217-333-6767; e-mail: