Cormorants lose ground on Island
Carrie West
Special to Times Colonist
July 24, 2005
Nicknamed the "crow duck" because of its black feathers and V-shaped formations in flight, the double-crested cormorant is very abundant in North America. In fact, other parts of Canada and the U.S. use culling programs to control large populations, considering these goose-sized birds pests that wreck environments and eat too many fish.
So with growing populations elsewhere, why did B.C. lose two-thirds of its crow ducks in 13 years? No one really knows. This dramatic decline in B.C. is a troubling statistic... and an unsolved mystery.
Our greatest colonies of double-crested cormorants are very close to Victoria. The largest is on Mandarte Island, near Sidney. That colony of 1,100 active nests in 1983, dipped to just 215 nests in the 2000 count. It's a similar story for the Great Chain Island near Oak Bay. Once hosting 686 nests, this island now has just 104.
Boats, kayaks and humans on shore can disturb nesting sites. The cormorants get scared. They take off and fly in big sweeping circles over the water, leaving undefended eggs and chicks for crafty gulls and crows. But bald eagles also scare the cormorants, especially the "big dumb juveniles" looking for easy food.
"I've seen them land right in the middle of the cormorant colony; flush all the cormorants. Cormorants do the same thing -- the big sweeping turns, panicking, freaking out. But then the gulls during that interlude and the crows will come in and just remove all the eggs so fast, even in an area with 50 or 60 nests.... And I've seen the eagle stand there and not take anything and not even seem to know what's going on," says John Elliott, a research scientist with the Canadian Wildlife Service.
Elliott says the cormorants return once the eagle is gone and lay more eggs the next night. In fact, these cormorants will start laying in May and keep trying to breed until August. Still, Elliott believes it's unfair to pin all the blame on eagles.
Elliott monitors double-crested cormorant eggs for such dangerous ocean chemicals as PCBs. Crow ducks eat fish close to shorelines. Thus, they make a great barometer of the continued presence of PCBs in our waters and the effect on our ecosystems. Environment Canada has tested double-crested cormorant eggs on Mandarte Island since 1970. Contaminants have been linked to birth defects in double-crested cormorants, but formal federal studies dried up in the mid-'90s, Elliott says.
Since then, PCB levels have remained reasonably constant and scientists don't believe they are the direct cause of our plunging double-crested cormorant populations. (But equally nasty fire retardant chemicals are on the rise and those also affect marine environments.)
An avian disease called Newcastle disease apparently killed 10,000 double-crested cormorants in Canada's Prairie provinces after a 1990 outbreak. Two B.C. colonies tested positive in 1993. A 2002 provincial report on double-crested cormorants said avian diseases should not be overlooked.
And another possible reason for our disappearing crow ducks is lack of food. There could be fewer little fish around for them to eat, due to changes in the marine environment and fishing practices. But again, those studies haven't been done.
Times Colonist
Sunday, July 24, 2005
DOUBLE-CRESTED CORMORANT
Species: Double-crested Cormorant
Location: Strait of Georgia and Juan de Fuca Strait; also Stum Lake (west of Williams Lake)
Official Status: Red listed (provincial)
Number remaining: 602 breeding pairs, or fewer than 2,000 (last published estimates)
Ecological significance: Abundant in North America (in fact, culls take place). B.C.'s population has decreased by two-thirds
Favourite food: Small fish
Key threats: Bald eagles, crows, glaucous-winged gulls; human disturbance. Also, marine environment (food supply); toxic contaminants
Carrie West can be reached at carriewest@telus.net.