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Birds 

Cormorants

Double-crested cormorants visit Grenadier Pond in the spring, before they settle in at their regular nesting grounds (most likely at Leslie Street Spit).

See also Cormorant FAQs


Double-Crested Cormorants
Double-crested Cormorant
Colin Marcano

Double-crested Cormorants (Phalacrocorax auritus) are large, black birds that are named for the two small tufts of feathers occurring on either side of their head. They are beautiful birds, with bright emerald green irises, blue, yellow or orange eyelids, and blue interiors of their mouths. They’re often easy to recognize by their habit of orienting themselves to the sun and spreading their wings in order to dry their feathers, and in some cases, to help regulate heat gain or loss.

Although there are thirty species of cormorants world-wide, there are only six in North America. Of these six species, the double-crested cormorant is not only the most widespread, but also the only one commonly found around inland fresh bodies of water.

Double-created cormorants feed primarily on small, and largely non-native and non-commercial fish, helping to keep populations of unwanted fish species in check. The majority of their diet is the non-native, invasive Alewife and Round Gobies, and they also commonly feed on abundant species like rainbow smelt and yellow perch.

Cormorants build large, shallow nests in trees and on the ground. They will gradually kill the trees they nest in through the deposition of their guano and by breaking branches for use in their nests. However, despite the damage these birds cause, the trees can continue to support them for long periods of time.

Double-crested Cormorants
Tony Pus

While there are historical accounts of double-crested cormorants in North America as early as 1604, they have experienced dramatic population changes over the last three decades. The widespread use of DDT caused a major population decline in North America, due to eggshell thinning, (meaning that the cormorants’ eggs would break before they had hatched and kill the embryos in the process), making them uncommon for some time. Double-crested cormorants were completely devastated by these chemicals, disappearing as a nesting species entirely on Lakes Michigan and Superior, and having only ten nesting pairs remaining on Lake Ontario at one point.

However, a ban on the use of DDT, as well as changes in the availability of the species’ prey base, led to an enormous population growth. From 1973 to 1993, the double-crested cormorant population witnessed a 300-fold increase to 38,000 pairs!

While this recovery is celebrated by some as an ecological miracle and success, it has caused great fear among many others, and has led to increasing cormorant and human conflicts (see Cormorant FAQs below). Some levels of government and groups have called for mass slaughters of these birds based on the ecological concern that the excrement of double-crested cormorants damages the trees they nest in, including on sandspits in the Great Lakes region. However, as noted above, double-crested cormorants do not kill as many trees as is claimed, as they re-use the same nests year after year, until the trees become too weak to use anymore, and in fact they prefer to use ground sites for nesting when they are available and the colony is safe from disturbance.

An Interesting Note About Cormorants! As they are a diving bird, species of cormorants have played a role in human fishing industries in Japan and China for more than 2000 years. In China, they were fully domesticated, with their eggs hatched and reared by human hands, their wings clipped, and training implemented to have them respond to their masters’ voice and whistle commands. A signal was given to have the birds dive for fish, and a long bamboo pole was used to have them jump on, after which they would be lifted into the boat.

Author: Barbi Lazarus


 
Cormorant FAQs

The following notes provided by Dr. Gail Fraser respond to some of the concerns and questions people may have about this species.

Adults with chicks
Dr. Gail Fraser

#1. "Cormorants will take over High Park."

Nesting cormorants are very sensitive to human disturbance. Thus it is unlikely that they will take up nesting in High Park given the volume of people that go through the area.

#2. "The management of High Park should be harassing/scaring off any cormorants which visit the park."

Where warranted as a management technique, harassment of cormorants requires a permit from the Ontario Ministry of Natural Resources. If this were ever to be considered, this management action should undergo community consultation.

#3. "Cormorants will eat all the fish in Grenadier Pond."

As long as there are natural hiding places in the pond, cormorants will not be able to catch all the fish.

''#4. "Cormorants will chase away other waterbird species such as Great Blue Herons because they will eat all of the fish."'

Herons and cormorants have completely different foraging habits and it is unlikely they compete for food. Cormorants are pursuit divers (i.e., they chase after fish underwater), whereas herons are waders (i.e., they walk along shorelines and hunt for a variety of organisms). This automatically means they are foraging in different places and catching different things.

#5. "Cormorants will damage the park's habitats."

There is no question that cormorants modify the habitat when they nest in trees (they will nest both on the ground and in trees) and the results may not be aesthetically pleasing, yet their presence is a conservation success story. Cormorants were virtually extirpated from this region in the 1960's. (See factsheet).

The changes cormorants cause to their habitat is a natural succession process; cormorants are a native bird in the Great Lakes landscape.

One of the most likely reasons habitat modification is seen as a problem is because humans have deforested much of southern Ontario and therefore greater value is placed on remaining green spaces. The number one driver of loss of biodiversity in southern Ontario is agriculture, not cormorants. Focusing on protection and expansion of natural areas which have existing high biodiversity is a good way to offset concerns about cormorants.

Author:

Dr. Gail S. Fraser, Faculty of Environmental Studies, York University

Dr. Fraser’s expertise is on the ecology of colonial nesting waterbirds.


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Content last modified on August 07, 2011, at 02:26 PM EST