Colonies of Caspian terns are becoming harder to find in Lakes Michigan and Huron.
James Ludwig is an ornithologist who has studied migratory birds in the region since the 1960s and just finished a trip across the Canadian waters of Lake Huron. He says he found about 100 Caspian tern nests where he found more than 1,900 in 1995.
Ludwig says the situation for Caspian terns is similar in the Michigan waters of the upper Great Lakes.
A colony that had long nested on Hat Island, near Beaver Island in northern Lake Michigan, was absent last year when researchers with the Seney National Wildlife Refuge visited. As recently as 2010, more than 300 nesting pairs of Caspian terns could be found on Hat Island.
Ludwig says most colonial waterbirds, like cormorants and herring gulls, are fewer in number in the areas he surveys. He says it’s because the amount of fish in the lakes is in a steady decline.
“The populations [of colonial waterbirds] are all going down and I have no idea how far they’re going to go down,” Ludwig says. “Some things may go virtually extinct, and in the upper Great Lakes it might be the Caspian tern”
But Ludwig says it is a different story in the lower Great Lakes, where fish are more abundant.
“I think an awful lot of these birds have simply relocated down into Lake Ontario and Lake Erie,” he says. “There are colonies in lake Ontario and Lake Erie that were never there twenty years ago.”
Ludwig says the situation could be different for double-crested cormorants. That’s because a small fish that has become more numerous in Lakes Michigan and Huron is the round goby. Gobies live on the bottom of the lake and terns can’t get at them but cormorants can.
For more than a decade, federal, state and tribal wildlife agencies have killed cormorants across the eastern U.S. to protect fish. A judge halted that program last month saying it was not clear all the killing was necessary.
Ludwig says the shift in the food base to gobies will move cormorant colonies closer to the mainland where gobies live, and likely fuel conflict between the birds and people.