Herons in Chicago Wetlands Survive Exposure to Banned Toxics

University of Illinois veterinary biosciences scientist Jeff Levengood, who led a newly published study of the herons, said chemicals banned 30 years ago for harmful effects on wildlife are still showing up in the herons' offspring.

Pair of black-crowned night-herons in nesting cover near Lake Calumet, in southeastern Chicago (Photo by Michael Jeffords, Illinois Natural History Survey)

The researchers found polychlorinated biphenyls, PCBs, and DDE in the eggs of the night-herons nesting in wetlands adjacent to Lake Calumet. These wetlands are surrounded by industrial developments along Lake Michigan near the Illinois-Indiana border.

PCBs were commonly used in electrical transformers and other industrial applications until they were banned in 1977 because of their toxicity in the environment.

DDE is a metabolic by-product of dichlorodiphenyltrichloroethane, commonly known as DDT, a pesticide banned in 1972 because it was observed to kill or disrupt the reproduction of birds and other wildlife.

The DDT ban is believed to have reversed the dramatic decline in the American bald eagle and the peregrine falcon in the continental United States.

Levengood, a wildlife toxicologist at the Illinois Natural History Survey, put together a research team with scientists from the U.S. Geological Survey, the Illinois Waste Management and Research Center, and Purdue and Duke universities.

They found that the Lake Calumet herons appear to be picking up the contamination primarily from Lake Michigan by means of an invasive fish, the alewife.

Alewives harbor comparable levels of PCBs and DDE in their tissues, Levengood said. The spawning season of the alewife in Lake Michigan coincides with the nesting season of the night-herons.

"The alewives come to shore to spawn when the first warm waters of spring run into the lake and the temperature starts to rise," he said. "There are untold millions of these things along the shore in April."

On several occasions the researchers saw large numbers of night-herons, "in some cases a hundred birds or more," along the sea walls on the southwest shore of Lake Michigan, Levengood said. "They'd be standing there peering into the water, and then they'd kind of do a belly flop into the water and grab a fish."

The researchers collected data over two years and conducted several genetic, biochemical and reproductive analyses to determine whether the chemical exposures were adversely affecting the birds.

They looked at DNA strand length, a measure of genetic damage, and oxidative stress, a contributor to aging and disease. They compared the number of eggs and the viability of the eggs and young chicks to those in other, less polluted reference colonies of black-crowned night-herons in Minnesota and Virginia.

"These were all normal compared to the reference colonies," Levengood said. The team found no evidence of eggshell-thinning, which is sometimes associated with exposure to DDE.

"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.

Populations of black-crowned night-herons in the Lake Calumet wetlands have fluctuated in the last 20 years, peaking at more than 1,500 birds in the early to mid-1990s.

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

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."

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

The study appears in the current issue of the "Journal of Great Lakes Research."

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