G'day all,
A bit of a technical question. I've been monitoring the mortality
rate of a few species at Alice Springs Sewage Ponds after a spike in
botulism poisoning last year.
I'm not a biologist, but what I've learnt is that "c" type
Clostridium botulinum bacteria reside and breed in anaerobic muds at
the bottom of the ponds. When we get the warmer weather the amount of
bacteria increases and bottom feeding birds (swans, diving ducks) can
stir it up and ingest it, resulting in the increased mortality that
we witness.
At the moment we are seeing a greater number of dead and moribund
birds around the ponds (mostly Black Swan, Hardhead, and the
occasional Grey Teal).
My question is this; why are the aforementioned species affected but
the grebes (Australasian and Hoary-headed) which are accomplished
divers have not been observed to be affected to this point. In 18
months, I have not found a single grebe carcass or seen any grebes
that seem effected by botulinum toxicity. I am at the ponds at least
twice a week so have a very good idea of the changes in populations
and movements there. We have a fairly stable population of between 80
and 120 grebes, and I'm surprised that they never seem to be affected
by this toxin which always seems to take out quite a few swans and
ducks (and the odd stilt and lapwing) each summer. I can only imagine
that there is some difference in their feeding technique or the
physiology of their digestive tract which keeps them safe from it.
Can anyone enlighten me?
Cheers,
Chris Watson
Alice Springs
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