(CP) - Tens of thousands of migratory water birds
will likely die on Lake Erie next year from botulism
poisoning if recent years are anything to go by, scientists
warn. And there's a danger the epidemic could spread
and actually threaten whole species, they say.
Over the past four years, the numbers of dying loons,
gulls and other fish-eating birds have risen dramatically
but the reasons have yet to be properly understood.
"It's a bit of a mystery," said Jon McCracken, an
ornithologist with Bird Studies Canada.
"Type E botulism has historically been very rare across
the entire planet, so historically we would see a small
outbreak maybe once every 10 or 15 years and quite localized,
so it's very unusual."
Scientists believe the potent toxin, produced by bacteria
that naturally live in lake sediment, is finding its
way into the aquatic food chain.
One theory is that filter-feeding zebra and quagga
mussel, exotic species that began invading the Great
Lakes in 1985, are concentrating the toxins.
Birds then feast either on fish such as the round
gobi, which favours the mussels, eat the mussels themselves,
or pick up the poison from animals that have already
died.
The poison paralyses respiratory muscles, or in the
case of water birds, causes drowning because they can't
keep their heads above water.
Death rates are hard to come by because there are
not enough people counting dead birds on the shorelines
while many simply sink to the bottom of the lake and
disappear.
However, it's believed that tens of thousands of birds
died between August and November this year on Lake Erie
and the Canadian Wildlife Service is predicting mass
deaths next year.
There's also the possibility of the epidemic spreading
to Lake Ontario.
While there's no immediate concern for most bird populations,
rare species, such as bald eagles, could be affected,
McCracken said.
If the outbreaks persist year after year, the impact
even on more abundant populations could become significant.
There are also fears the loons on Lake Erie, many
of which may come from the northern prairies, could
carry the disease back home and cause problems there.
McCracken said studies are badly needed to assess
the role that changes in climate, water temperature,
lake water levels, and invasive species are playing
in the development of the outbreaks.
