Biology
Identification – Double-crested Cormorants are likely the only cormorant species to be seen in the Great Lakes region. About the size of a small goose, from far away the Double-crested Cormorant can appear somewhat of a lackluster black bird. Closer inspection reveals many beautiful details of their appearance.
Vibrant jade green eyes stand out remarkably against its iridescent green-black feathered body, encircled by what could best be described as some kind of electric-blue dotted eye-liner. Surrounding its long (5-8 cm) and slender hooked bill is a blazing path of orange-yellow skin.
In mating season, both male and females develop tufts of black and white feathers behind their eyes, giving them their name. They often fly singly or in small flocks; flying in a single line or V-formation.
Diet – In general, the cormorant’s diet is a reflection of where they feed. Within the Great Lakes the majority of their diet is composed of invasive species such as Alewives and Round Gobies, non-commercial fish such as sticklebacks and extremely abundant species such as Yellow Perch, as well as 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.
Populations
Cormorant populations have been increasing the past few decades throughout Ontario. Non-native 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.
Legislation
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.
History
Despite common beliefs, Double-crested Cormorants are not new to Ontario. They are a native bird, 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. Today cormorants are found throughout the Great Lakes and in many inland lakes and rivers in Ontario.
- Cormorant Voices from the Grave: How Abundant Was Pre-Columbian Wildlife?
Barry Kent MacKay addresses how and why damaging myths have prevailed in regards to the history of the Double-crested Cormorant and their population size over time. - Historic Populations of the Double-crested Cormorant (Phalacrocorax auritus): Implications for Conservation and Management in the 21st Century
An academic article detailing specific historic (pre-1900) breeding distribution of Double-crested Cormorants in North America, and a discussion on conservation versus management goals. - Environment Canada’s fact sheet: The Rise of the Double-crested Cormorant on the Great Lakes: Winning the War Against Contaminants
Outlines the birds history in the Great Lakes – from their initial colonization, to their rapid decline due to toxic chemicals, and their eventual return as a result of decreasing levels of contaminants and human influence on fish stocks. - Dawson, W. (1903) The birds of Ohio: A complete and scientific popular description of the 320 species of birds found in the state. This book describes the Double-crested Cormorants appearance, nesting habits, range, and even details significant declines in their population numbers due to persecution from anglers and hunters.
- Grosvenor, G. & Wetrnore, A. (1932). The Book of Birds: Volume One, National Geographic Society. Provides an early account of Double-crested Cormorant behaviour and human interaction. Includes a description of the early Geographical Society of Canada’s study investigating stomach contents of cormorants in response to their persecution. Upon finding no trace of salmon in the birds diet, the 25 cent bounty placed on each birds head by fishing clubs was withdrawn.