UPDATED 08/30/11 10:04 a.m.

CHICAGO (CBS) — The waterfowl that have recently died en masse at the Park District’s McKinley Park, and elsewhere in the Chicago area, were suffering from avian botulism.

The Chicago Department of Animal Care and Control confirmed that the birds died of botulism type C.

WBBM Newsradio’s John Cody reports more than 30 birds have been found dead at McKinley Park, 2210 W. Pershing Road, and two other city parks.

Annette Prince, of the Chicago Audubon Society said before the Animal Care adn Control report that the birds’ symptoms resembled that of avian botulism.

“We know that there have been other areas and places in the Chicago area where birds have been found with avian botulism,” Prince said. “It’s a condition that develops particularly during high-temperature situations.”

Prince says avian botulism weakens the muscles in the wings, and legs and in the neck, which means some birds drown because they can’t raise their heads out of the water.

Prince, who also serves as director of Chicago’s Bird Collision Network, says the first victim in early August was a swan at McKinley Park. Most of the other bird victims have been Canada geese, along with a few mallard ducks.

Lagoon maintenance worker Lorenzo Torres told CBS 2’s Derrick Blakley earlier this month that he had never seen so many dead geese at the park at one time.

“We find once in a while, like once a month and that’s it,” he said. “Maybe a total, maybe five geese a year.”

While most have been in McKinley Park and other parks, Prince says the deceased birds have even been found in Lake Michigan.

“We have picked up a couple in Lake Michigan,” she said. “Now, whether the avian botulism is actually in Lake Michigan, or whether these birds acquired it at a different location and then were found in Lake Michigan” is not known.

Prince says a few water fowl have survived after being taken for treatment at the Willowbrook Wildlife Haven.

Prince says avian botulism flourishes when temperatures are high and water levels fluctuate – reviving dormant bacterial spores.

She says she hopes that if the problem is indeed botulism, that it will end with the arrival of the current cooler temperatures.

Meanwhile, warnings have been posted at McKinley Park, and at nearby McGuane Park at 2910 S. Poplar Ave.

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