- 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."
-
- © Copyright 2004 Bell Globemedia Publishing Inc.
All Rights Reserved.
-
- http://www.theglobeandmail.com/servlet/story/RTGAM.20041126.wfrogs27/BNStory/Front/
|
