Information about sick and dying cormorants in Toronto

For the past three weeks, we have had many reports of sick and dying cormorants at Tommy Thompson Park, Toronto Islands and across the waterfront. Preliminary tests suggest Newcastle, which commonly impacts juvenile cormorants and poultry.

Cormorants in Toronto

Double-crested Cormorants are a species native to the Great Lakes, but whose population was nearly extirpated (local extinction) in the latter part of the 20th century. As such, their dramatic population recovery in Toronto since 1990 is often perceived as a non-native invasion. Tommy Thompson Park is home to the largest breeding colony of Double-crested Cormorants in North America, with 14,500 nests recorded in June 2018. With 2 adults per nest, an average of 2 chicks per nest, plus non-breeding adults and juveniles from 2017, our current population estimate is about 60,000 to 70,000 individuals.

Cormorant Management in Toronto

While cormorant populations in North America are usually managed to achieve a target population number, a different approach has been taken by Toronto and Region Conservation Authority (TRCA). Since 2008 cormorants at Tommy Thompson Park have been managed spatially, to encourage ground nesting and prevent tree nesting within healthy trees in the park. This is primarily accomplished by implementing an escalating scale of deterrent activities in defined areas throughout the breeding season from April to early June. This technique has been highly successful, with 74% of the population nesting on the ground in 2018 compared to 15% in 2008. Further, we have prevented further impacts to trees during this time period. Additional information about our management strategy can be found online at

Newcastle Disease

Newcastle disease is a virus that impacts the respiratory, neurological and gastrointestinal systems in birds, and is transmitted through direct contact with infected or carrier individuals. Juvenile cormorants are particularly susceptible, while other wild bird species and adult cormorants are typically immune. Sick Toronto cormorants are displaying typical symptoms including inability to walk or fly; lack of muscular coordination; paralysis of one or both legs or wings; twisting of the head and neck; and walking in circles. They have been observed walking down trails and have lost their fear of humans. This disease is fatal once contracted. The Canadian Food Inspection Agency has a fact sheet online at

Natural Population Management

It is to be expected, and is completely natural, for disease to spread through large populations of wildlife – it is one way that nature restores balance when a population becomes too large. So far there are reports of about 100 individuals that have died from the disease. This is a very small percentage of the 60,000 – 70,000 individuals in the Tommy Thompson Park colony.

What to do with sick cormorants

While difficult for compassionate people to watch, this is a natural process and it is our recommendation that cormorants be left alone. If this is not possible, Toronto Animal Services may be contacted for humane euthanasia.

What to do with dead cormorants

Park managers/property owners that come across dead cormorants should bury the carcasses in deep holes to prevent scavengers from digging them up. Anyone moving carcasses should wear disposable gloves, use garbage bags (though don’t bury the bag), and equipment. Minimal handling of the carcasses is advised. Thoroughly wash hands with soap after the burial is complete.