Fact Sheet

Double-crested Cormorants in Ontario



Double-crested Cormorants are not new to Ontario; they are known to have been a resident of Lake of the Woods since 1798.  The earliest nesting record for cormorants in Ontario is from Black Bay in Lake Superior in 1920. By 1931, cormorants were breeding in Lake Huron and by 1938 they were breeding in Lake Ontario.  Today cormorants are found throughout the Great Lakes and in many inland lakes and rivers in Ontario.



Identification – Double-crested Cormorants are likely the only cormorant species to be seen in the Great Lakes region.  Cormorants are about the size of a small goose and have a uniform shiny greenish-black feather colouring.  The bill is long (5-8 cm), slender and hooked at the end.  They often fly singly or in small flocks flying in a single line or V-formation. Cormorants are fish eating birds and consume small bait-sized fish and some aquatic insects.


Range – Cormorants breed in Canada as far west as Alberta and easterly to the Atlantic Coast including Newfoundland. In Ontario, they are found throughout the Great Lakes and have a breeding range that extends north up to Southern James Bay and Lake Abitibi.  Cormorants that breed in Ontario typically spend winter months in southern United States. 


Breeding – Cormorants are sexually mature by 3 years of age.  Both male and female cormorants take care of the nest and young. Cormorants are a long-lived bird species and in the wild have been known to live for up to 23 years.


Nesting – Cormorants are a colonial nester selecting islands as breeding areas.  Nests are found on the ground or within the upper branches of trees, directly adjacent to water.  Nests are composed of sticks, leaves, weed stalks and other available material.  Cormorants lay an average of 3-4 pale greenish-blue eggs with a chalky covering. 



Cormorant populations have been increasing the past few decades throughout Ontario.  Nonnative baitfish in the Great Lakes, such as smelt and alewives, has provided an ample source of food for cormorants. As well, a reduction of toxins such as DDT has enabled cormorant populations to increase.  Cormorants have been dispersing into new habitats and expanding their North American range.  In some areas of Ontario, their recent rapid expansion has had impacts on terrestrial and aquatic environments and has resulted in increased public concern. 



In Ontario cormorants are protected under the Fish and Wildlife Conservation Act (FWCA). 

Cormorants are not a game species and cannot be hunted.  Under Subsection 31(1) of The Fish and Wildlife Conservation Act (FWCA), an individual who believes on reasonable grounds that cormorants are damaging or are about to damage their property can harass, capture or kill the cormorants on their own property.  



Protection of Property

Cormorants are known to kill trees used for roosting or breeding sites.  The death of the trees and under-story vegetation occurs due to deposition of guano.  Under provisions of the FWCA the destruction of trees and vegetation on private property or depredation of fish from a privately owned aqua-culture facility, may constitute reasonable grounds to harass, capture or kill cormorants.  Cormorants are very susceptible to disturbance; therefore harassment techniques can be quite effective.  Constant human presence on an island during nesting or roosting periods will discourage cormorants from using an island.  In situations where constant presence isn’t possible, then, harassment techniques such as using bangers or air horns may deter cormorants.  As a last measure landowners may kill cormorants to protect property.  The FWCA requires that there be no unnecessary suffering to the birds and that control is limited only to the number of birds that is necessary to protect the property. Dispatch of adult nesting cormorants would deprive the hatch of sustenance and shelter and cause it to suffer. Landowners who chose to exercise their rights to protect private property should only do so at a time and in a manner that would not cause unnecessary suffering to adult cormorants or their progeny.


 A landowner may acquire an agent to do the harassment or killing of cormorants that are damaging property if the person belongs to a class of agents prescribed by the regulations or has an authorization from the Ministry of Natural Resources.


Eggs or nests cannot be disturbed without authorization by the Ministry of Natural Resources. 


Cormorants on Crown Land

Cormorant breeding and roosting colonies on Crown lands are protected under the FWCA.  It is illegal to harass, capture or kill cormorants on Crown land, including cormorants swimming in or flying over lakes and rivers.  


Current Status

The Ministry of Natural Resources is interested in cormorant populations throughout Ontario and has been involved in cormorant monitoring and research in a number of areas.  Recently, Presqu’ile Provincial Park has been actively managing cormorant populations to prevent negative impacts on the park ecosystem.


The MNR is working with the Canadian and U.S. federal governments and other Provincial and State governments in North America to share information about cormorant populations.  


MNR has assisted the Canadian Wildlife Service in monitoring population trends of all colonial nesting water birds on Lakes Huron, Erie and Ontario.  MNR is also aware of many inland lake cormorant populations and in some cases has been involved in providing breeding evidence to the Ontario Breeding Bird Atlas.  


The ministry is committed to maintaining a diversity of environments in Ontario and this includes habitat for cormorants. Future management for cormorant populations will be determined based on results of current research and will involve consultation with stakeholder groups and interested clients.  

For more information on cormorants please contact your nearest District MNR office.