Start eating those legs… or be eaten

I keep hearing that frogs are “canaries in the mine”, their decrease in numbers warning of imminent environmental catastrophe. So it was with interest, and I confess, some amusement, when I read about the invasion of American Bullfrogs into British Columbia.

Wayne Campbell, former chief ornithologist of B.C. and the author of numerous bird books, said he went to investigate the stories of the Cranberry Lake bullfrogs a few springs ago, and was shocked by what he found.

“There was a big bullfrog floating on the surface, dead. Turns out it had choked, trying to swallow a gosling.”

“A small duck doesn’t stand a hope in hell. They are like alligators. I’ll tell you, boy, don’t put your fingers over the side of the boat.”

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Waterfowl beware: Hungry killer bullfrogs are on the loose in B.C.

By MARK HUME
Globe and Mail Update

UPDATED AT 1:12 AM EST Saturday, Nov 27, 2004

Vancouver — When American bullfrogs were first imported to British Columbia in the 1930s, the idea was that their legs would end up on dinner plates. Instead, the frog farms failed; the stock got free, and now the giant bullfrogs are the ones doing the eating, attacking everything from tiny tree frogs to waterfowl.

Some municipalities are talking of halting the bullfrog invasion by building “control corridors,” where the rapidly expanding population would be electroshocked and killed by freezing.

Clyde Burton, a naturalist in Powell River, said such controls might have helped if they had been in place years ago on the Sunshine Coast, where bullfrogs are blamed for wiping out the Cranberry Lake duck population.

“They will eat just about anything,” said Mr. Burton, who over the seasons has heard the deep, honking sound of bullfrogs displace the songs of water birds on the lake, about 120 kilometres north of Vancouver.

“A small duck doesn’t stand a hope in hell. They are like alligators. I’ll tell you, boy, don’t put your fingers over the side of the boat.”

Mr. Burton said he first realized bullfrogs were eating birds a few years ago. He was standing in a marshy area on Cranberry Lake when a flock of small sandpipers landed.

“There was a big splash, and the flock took off,” Mr. Burton recalled. “By the time I got over there to have a look, here was this bullfrog with a sandpiper in its mouth, just the corner of the wings sticking out.”

Mr. Burton said he started catching bullfrogs after that to study stomach contents because he wanted to know if the sandpiper incident was just a case of one killer frog.

He soon found grisly proof that the scientific name for American bullfrogs, Rana catesbeiana, might as well be Latin for ready to eat anything.

“We had one with two newly hatched wood ducks in its belly. We got one with a male yellow-rumped warbler. We got mice.”

Mr. Burton blames the bullfrogs, which he said stretch 40 centimetres toe tip to toe tip, for the lack of waterfowl on what was once a busy duck pond.

“I used to go over there on Mothers’ Day and count 150 ducklings. Now you see zero,” Mr. Burton said.

Wayne Campbell, former chief ornithologist of B.C. and the author of numerous bird books, said he went to investigate the stories of the Cranberry Lake bullfrogs a few springs ago, and was shocked by what he found.

“There was a big bullfrog floating on the surface, dead. Turns out it had choked, trying to swallow a gosling.”

He said he heard stories about bullfrogs jumping at small songbirds.

Mr. Campbell said bullfrogs have spread from Vancouver to Powell River on the mainland coast and from Victoria to Campbell River, on Vancouver Island.

Although found naturally in much of southeastern Canada, the bullfrogs are an alien species in B.C. and Mr. Campbell said cold temperatures should stop them from spreading much farther.

But they are already posing a serious environmental problem because of their voracious appetite, he said.

“It’s a difficult problem that should be tackled. It requires a team [of experts] to get together. But I don’t know how you get rid of these darned things.”

Purnima Govindarajulu, a University of Victoria PhD student studying bullfrogs in B.C., said any chance of containing them was lost when the frog farms set them free.

Since then, they have migrated along ditches and with human help.

“People are moving them from place to place,” she said. “They have heard frog populations are dwindling, so they think they will help out by introducing them to a local lake or pond. In fact, it has the opposite effect, because native red-legged frogs are a main part of their diet.”

Ms. Govindarajulu said people have also helped the bullfrogs by removing trees and brush, creating more favourable conditions by warming the water.

In Greater Victoria, Stan Orchard, an expert on amphibians, has proposed a long-term eradication project modelled on the program Alberta uses to keep rats out of the province.

Ms. Govindarajulu doubts it will work.

“Once bullfrogs are established, they are almost impossible to eradicate,” she said. “Each female lays about 13,000 eggs. So you just need one breeding pair to escape and the population will explode again.”