The Double-crested cormorant

By Jeanette Rive
Walking along the Canal or Dow’s Lake, you may have noticed a black bird flying low above the water. Or a bird with a snake-like neck briefly surfacing before diving again. Or several of the dark birds roosting in the trees on Pig Island or on the rocks on Dow’s Lake, wings unfolded to dry their feathers. It’s the Double-crested cormorant, a bird native to North America, related to the booby and the frigate bird. One of six species of cormorant found in North America, it’s the most common one in the Ottawa area, although there was great excitement in the birding community a few years ago when a Neotropic cormorant, smaller and much browner than our common residents, spent some time on Dow’s Lake. The name cormorant is a contraction of two Latin words “corvus” and “marinus” which when combined mean “sea raven.”

Cormorants almost became extinct in much of Canada due to hunting, but they are abundant now and are considered pests by many. They consume vast quantities of fish. Their guano destroys trees where cormorants set up colonies. And there was a misguided belief that they weren’t native and were a threat to local nesting populations of native gulls and herons. Before it was banned in the early 1970s, the pesticide DDT also affected their breeding cycle. But like the Bald eagle, cormorants have recovered well.

The Double-crested cormorant – the crest is only visible during mating season – is quite large, 70-90 cm in length with a wingspan of about 120 cm, and it weighs between 1.2 and 2.5 kg. It has bright, light-blue eyes, and its mouth, bright blue on the inside, is visible when it hisses at other birds or when a male greets a female as part of the mating ritual. Cormorants are entirely matte black except for a bare patch of orange-yellow facial skin.
Unlike other waterfowl such as ducks, they don’t produce much preen oil so their feathers get water-logged when they dive. This is thought to be an adaptation to counter buoyancy – they can dive deeper because air bubbles do not get trapped under water-logged feathers. Because their bodies are adapted for swimming and diving, they expend more energy in flying than any other bird.

They are impressive fishers and divers – some cormorants can dive as deep as 45 metres and can hold their breath for several minutes. They chase fish underwater, propelled by webbed feet and using wings as rudders. Small fish are consumed immediately; just like Great blue herons, they bring larger fish to the surface and toss them in the air to so they go down the throat head first. Their upper bill is hooked, which is useful for catching prey. They also eat crustaceans, amphibians and some insects.

Cormorants are gregarious birds, nesting in large colonies. There are colonies along parts of the Rideau and Ottawa rivers, including near the Chief William Commanda Bridge and Conroy Island in Gatineau. Choosing a new mate every year, the male will find a nesting site, showing off his crests and the bright colours of his neck and eyes, waving his outstretched wings to attract the female. Both build the nest, made up of small twigs, bits of debris, seaweed and grasses. Quite large, about 75 cm in diameter, the nest can be on the ground, on rocks or in a tree. If a nest is left unguarded, other cormorants will pilfer building material for their own nest. On average, five pale blue eggs are laid and incubated for almost four weeks. Chicks are tended another three to four weeks before leaving the nest.

In some Asian and South American cultures, cormorants have traditionally been trained to catch fish. A loop was tied around the bird’s throat, allowing only small fish to pass and trapping larger fish in the gills. Along the Li River in China, for example, there was a belief that cormorants were very intelligent because they knew they were allowed to swallow every eighth fish. Once the bird had caught and delivered the seventh, it would refuse to dive again until it was allowed to eat the eighth. This practice has mostly died out and is now primarily performed for the tourist trade.

Cormorants are migratory, and ours will be heading to the Atlantic Ocean for the winter. This fall has been very mild, and the cormorants may stay around longer. After the water level in the Canal and Dow’s Lake is lowered for the winter, many migratory birds take advantage of the exposed shoreline to fish and refuel before flying to their winter destination.

Jeanette Rive is a Glebe bird enthusiast and frequent Glebe Report contributor.