Saturday, September 12, 2026

“Cormorant Overpopulation Wreaks Havoc on Toronto Islands”

Share

LISTEN | Are they causing issues that need to be controlled, or essential members of ecosystems that require protection?:

Double-crested cormorants are creating disturbances on the Toronto islands, primarily due to their widespread excrement.

Their feces, known as guano, is not only causing an unpleasant environment but is also damaging the trees they inhabit due to its acidic nature.

Concerns have been raised by Warren Hoselton, a former park supervisor on the islands, about the escalating environmental impact caused by the cormorants.

The population of these birds at Hanlan’s Point has surged to around 18,000, leading to a threefold increase in the past year, as reported by the Toronto and Region Conservation Authority (TRCA).

Local residents and visitors on the islands are advocating for the relocation of the cormorants to mitigate the issues they are causing.

Why the Controversy Surrounding These Birds?

The detrimental effects of cormorant guano have transformed the once lush green shoreline into a dystopian landscape.

Gordon Ballantyne, the general manager at the Toronto Island Marina, described the situation as an environmental catastrophe for the forested areas.

A man stands on a boat with a shoreline in the background and birds nesting in trees.
Warren Honselton criticizes the lack of actions against cormorants on Toronto islands, which are wreaking havoc on the trees they inhabit. (John Chipman/CBC)

Ballantyne highlighted a significant decline in boat traffic at Hanlan’s Point due to the cormorants’ activities, causing inconveniences and disturbances for boat owners.

Their Migration Story

It is speculated that the cormorants originated from a nearby colony at Tommy Thompson Park on Toronto’s mainland.

The TRCA noted a correlation between the declining population at Tommy Thompson Park and the sudden increase in cormorants on the Toronto islands in 2022.

The presence of predators at the mainland colony, particularly raccoons preying on cormorant chicks, might have prompted the birds to seek safer nesting grounds.

A large group of birds nesting on the ground.
This image showcases the cormorant population residing at Tommy Thompson Park in 2025. (Submitted by Gail Fraser)

Gail Fraser, an avian ecologist at York University, suggested that the stress from predators might have prompted the cormorants’ migration.

Exploring Solutions

In some regions of Canada, cormorants can be culled to manage their populations, but a bylaw in Toronto prohibits such actions within city limits.

The TRCA, representing the City of Toronto, is actively involved in managing the cormorant population at Tommy Thompson Park.

The focus is on discour

Read more

Local News