The Double-crested Cormorants have been returning to the province for the last week or so. I saw a flock of 125 floating as a raft down the St. John River at Crock's Point last weekend (April 16) and there was a report of about 400 roosting on the piers of the former Fredericton bridge that same weekend. They were migrating up the St. John River in large numbers.
The Double-crested Cormorant (Nannopterum auritum) was classified as the Phalacrocorax genus until 2021 when the genus was changed to Nannopterum by the IOC. The genus name, Nannopterum, means small winged which came from a flightless member of the family. The auritum means 'eared' which comes from the nuptial crests.
Cormorants are long-necked diving birds of which there are 6 species in North America. In New Brunswick we have 2 species, the Double-crested Cormorant and the Great Cormorant. For more information on the Great Cormorant, search this blog. Cormorants in general have long necks, long, heavy bodies, stiff tails and long, hooked bills. The Double-crested Cormorants are large birds, 70-90 cm long (28-35 inches). They feed mainly on fish but also amphibians and crustaceans which the catch underwater by swimming swiftly with the strong propulsion of their feet. They get their feathers wet while swimming in order to reduce their buoyancy. After a feeding session they perch and dry their wings by perching and spreading them out. That is a characteristic cormorant sight. See the photo below.
So what about the crests? In breeding plumage they sometimes show a pair of tiny crests/plumes on the top of the head which can be black, white or peppered. The white crests/plumes are more often seen in the north and west of their range.
The Double-crested Cormorant likes both salt and fresh water unlike the Great Cormorant which also occurs here. In order to tell the two species apart you have to take a close look to check for the larger size of the Great Cormorant and its white chin patch and white flank patch.
The range of the Double-crested Cormorant covers most of North America except the far north. They breed in most of southern Canada and the US including all of the Atlantic provinces. A few are beginning to remain here for most of the winter along our coasts. They winter on the west coast from Alaska to the Baja Peninsula and in the east from southern Maine to the Yucatan Peninsula.
During the breeding season the male has an elaborate courtship dance in which he presents the female with nesting materials and points out a suitable nesting site. The nest is built of twigs and seaweed and in it the female lays two pale blue eggs. Both adults incubate the eggs for 28 to 30 days.
The vocals of this species are not spectacular to humans. Their deep guttural grunts are part of the aquatic landscape. Because they are gregarious birds and often found in colonies, they can be loud.
Today the population size of the Double-crested Cormorant is healthy and increasing. In the 1960s their numbers decreased due to DDT poisoning. Because they are perceived as being detrimental to the fish stocks, there has been some loss by humans destroying them. In recent years their population has increased probably due to less contaminants in the water and the rise of the aquaculture industry. They have increased in the Great Lakes region due to the rise in the non-native species of fish, the alewife. In some places culling operations have taken place to control the Double-crested Cormorant population.
In the wild the Double-crested Cormorant life expectancy is 6 years. The oldest documented wild Double-crested Cormorant lived to be at least 17 years 9 months.
No comments:
Post a Comment