Cormorants have taken over the Toronto Islands. The reason? Two bald eagles

Officials with the Toronto Regional Conservation Authority (TRCA) say an effort to remove thousands of cormorants from the Toronto Islands was going well until two bald eagles showed up over the winter.

Though it is considered a milestone for the bald eagles to call Centre Island home, the population of cormorants has doubled this summer.

The TRCA has been trying to safely move cormorants off the island and back to their home at Tommy Thompson Park, but because eagles are sensitive to humans, they had to create a 100-metre buffer from the eagle’s nest and stop using tools to relocate the cormorants.

“We had a plan for 2024 to triple our resources and really try to ensure that we minimize cormorant nesting at Toronto Island Park, but in the winter, when the cormorants were down south, a pair of bald eagles decided to take over a cormorant nest,” said Karen McDonald, the TRCA’s Senior Manager of Ecosystem Management.

“We are not going to take a nest count until the leaves fall off during the fall, but we estimate there is a nest count of about 2,000 [cormorants] near this eagle nest.”

Large population of cormorants a problem for Toronto Islands?

Cormorants are medium to large birds with long bodies and necks found in freshwater and marine environments worldwide. They feed on fish and nest in colonies, often on cliffs, islands, or trees near water.

You don’t need to travel far through the Toronto Islands to catch a glimpse of these birds that have completely taken over.

“Cormorants are interesting birds as they kill the trees in which they nest. A few actions kill the trees, notably their guano or droppings, which are very acidic,” McDonald said. “Killing the trees and stopping them from growing; when they are all nesting in one location and pooping in one location, you can imagine the smell is not pleasant.”

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Some experts, like Gail Fraser from the Faculty of Environmental and Urban Change at York University, believe the large presence of cormorants is a good thing.

“I like to think about the presence of cormorants, which means that there’s a pretty healthy ecosystem supporting them,” she said.

“I’ve seen boaters come right up to the colony. They get on to the colony while the birds are nesting. I’ve seen windsails come by. If we want the birds to return to Tommy Thompson Park, we also need to manage the waters around the park to reduce the amount of human disturbances.”

McDonald said that the bald eagles had two healthy, flying eaglets, that the birds responded well, and that their efforts to remove the cormorants safely were not affected.

The TRCA will be more aggressive in relocating the birds back to Tommy Thompson Park, and they hope to have their numbers reduced by next year.