Seven dead geese and two dead mallard ducks were collected Thursday from near an island in a lagoon in McKinley Park, the Chicago Tribune reported.
That brings the total of dead birds found in the park since the first ones were discovered Tuesday to 25, the newspaper said.
The Chicago Commission on Animal Care said it was working with the U.S. Department of Agriculture to determine the source of the problem, and several of the birds were undergoing necropsies and toxicology tests at a lab.
While a Chicago Park District official has initially said poisoning was suspected, Animal Care Executive Director Cherie Travis said that has not been confirmed.
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