Why aren't grebes affected?
Probably because they take live, moving food.
I was once able to watch an Australasian Grebe hunting in very shallow
water at The Briars (Mornington,Vic). Its search pattern was to swim in
zigzags, each leg being 6 to 10 feet long. Whenever it spotted prey, it
swam off at a different and unpredictable angle, obviously in pursuit,
often travelling quite a long way, before it either gave up or came up
swallowing something.
It was hunting under a complete cover of small duckweed, but it was
leaving 'footprints' on the surface, like the oar-traces of a sculler,
so it was easy to follow its movements till it got into deeper water.
Anthea Fleming
On 8/02/2012 3:56 PM, Andrew Hobbs wrote:
Hmm,
Feretting around in the mud is an almost full time occupation for some
ducks and swans so the question that comes to mind is 'why do ducks and
swans suffer from botulism'. I would have thought that it would have
been a sufficiently strong selection pressure to either develop a
different food source, develop an immunity or perhaps botulism is only a
very recent phenomenon in such conditions.
Any ideas?
Cheers
Andrew
On 8/02/2012 12:24 PM, Peter Shute wrote:
Is it possible that the grebes are being poisoned too, but aren't
dying in such visible places?
Peter Shute
-----Original Message-----
From:
On Behalf Of
Carl Clifford
Sent: Wednesday, 8 February 2012 1:52 PM
To: Chris Watson
Cc:
Subject: Re: [Birding-Aus] Botulism poisoning in waterfowl
Chris,
Though Grebes are divers, they feed on crustaceans, fish etc
and tend
not to go poking around in the mud at the bottom of the
ponds. Diving
ducks tend to ferret around in the bottom mud and would be
more likely
to get into the anaerobic layers.
Cheers,
Carl Clifford
On 08/02/2012, at 1:28 PM, Chris Watson wrote:
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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