They're Toronto Islands' newest visitors, but residents hope cormorants don't stay long

Hanlan's Point may be a popular destination for Torontonians in the summer, but the city and conservation officials say they're working to deter some unwanted visitors — a population of double-crested cormorants — from nesting in an environmentally sensitive area nearby.

The Toronto and Region Conservation Authority (TRCA) said it got word in May that the birds began appearing near Blockhouse Bay and Long Pond near the Hanlan's Point ferry deck at the west end of the Toronto Islands.

"There was a large increase in cormorants at the very beginning of June. And so we took immediate action to develop a sort of short-term mitigation strategy," said Andrea Chreston, the TRCA's project manager for Tommy Thompson Park.

Island residents worry about the damage the birds cause to trees. They're also not fond of the distinct odour from the cormorants' fish-based diet and their excrement. The TRCA says it's working to prevent them from nesting and expanding their footprint. But some experts say given the proximity to Tommy Thompson Park on the Leslie Street Spit, their arrival on the islands doesn't come as a surprise.

Cormorants are a native species that was in decline in the 1800s due to hunting and came close to local extinction in the 1970s and 1980s due to the use of DDT insecticide. The largest breeding colony of double-crested cormorants in North America is now at Tommy Thompson Park. Last year, there was an estimated population of 12,000 birds. 

The TRCA manages the colony and works to contain the area where they nest because their acidic excrement can damage trees.

"The excrement sort of rains down and it changes the soil chemistry. So the nutrients are no longer sort of readily available in the soil that the tree needs to absorb," Chreston said.."And so over time, the health of the tree declines."

But their droppings aren't the only problem. Chreston says the cormorants can strip the trees of their leaves by repeatedly nesting in them over a period of years.

She says the TRCA is also trying to set up ground nests to encourage the birds to stay away from the trees.

She says when they learned the birds began nesting on Toronto Island, they moved in quickly.

"We removed immature nests during June to the point where we were no longer seeing cormorants attempting to build new nests," said Chreston.

As it's now the end of breeding season, Chreston says conservation workers will return in a few months when the birds fly south for winter and remove all nest material so when the cormorants come back next spring, it'll be empty.

"We want to encourage cormorants that have nested at the Toronto Islands to come and nest on the ground at Tommy Thompson Park."

Some residents on the Toronto Islands are not yet sure what to make of the birds.