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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Hi,
All good points. Of course I knew about botulinum toxicity and that it could affect birds but I hadn’t realized the extent or its importance. The recent post to Birding Aus set me looking further. One reference which I found quite interesting was “Field Manual of Wildlife Diseases” published by the USGS.
http://www.nwhc.usgs.gov/publications/field_manual/
It has lots of interesting information and some of it supports your suggestions, with regard to human activity and effects, in the first paragraph.
The selective pressure must now be quite high (at least in recent times). The reference indicates that die offs of waterbirds due to botulinum toxicity of the order of hundreds of thousands to millions are relatively common in North America, and that it is the major cause of death in waders. Perhaps we will see an increase in resistance/insensitivity as birds evolve.
Cheers
Andrew
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I accidentally posted this response to Andrew Hobbs yesterday, instead of to the whole Birding-aus list.
Cheers, Stephen
Stephen Ambrose Ryde NSW
Hi Andrew,
The question I would be posing in the light of your query is how recently evolved are the current molecular structures of the neurotoxins of the Clostridium botulinum? Perhaps Clostridium botulinum is a recently evolved bacterium (in the evolutionary history of waterfowl) and/or its neurotoxins are recently evolved proteins. If so, perhaps there has not been enough time for ducks and swans to evolve a mechanism of resistance to the neurotoxins.
Stephen Ambrose Ryde NSW
I wasn’t actually thinking of acquired immunity. I was thinking more of evolved immunity. Botulinum toxin (a group of 7 or 8 individual toxins from /Clostridium botulinum and other related species./) and Tetanus toxin (from /Clostridium tetani //) /are all proteins, and target membrane proteins in their action. So mutants resistant to the toxins should be possible. Indeed while humans, mice etc are very sensitive to tetanus toxins, dogs, rats, some birds, snakes and amphibians are much less sensitive and turtles apparently are insensitive to the toxin. Also there is a range of sensitivities to botulinum toxins in humans with some humans being insensitive (Schiavo et al Physiol RevJanuary 2000 vol. 80 no. 2 717-766 ). So it should be eminently feasible for ducks and swans to have evolved immunity or insensitivity to the toxins too. I suspect that such ducks and swans have been ferreting around in the ooze for a long time so the question is still, why are they affected, and has it changed recently. (however you define recently).
Cheers
Andrew
/// /
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Andrew,
The problem with Botulism is, that the cause of death is not from infection by Clostridium botulinum, but from neurotoxins produced by the bacteria. The botulinum toxins have LD50s of less than 100 nanograms per Kg. Hydrogen Cyanide has an LD50 of only 1-3g/Kg
In Thomas, Hunter and Atkinson’s “Infectious Diseases of Wild Birds”, P. 405, they state that natural immunity does not play a significant role in Botulism, because “The toxin is so poisonous that the amount required to immunise an animal is much higher than the lethal dose.” They do say that it has been observed that naturally occurring antibodies to several botulinum neurotoxins were found in several carrion eating species of birds.
Cheers,
Carl Clifford
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
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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
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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
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Is it possible that the grebes are being poisoned too, but aren’t dying in such visible places?
Peter Shute
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Hi Chris,
A response from the AWHN:
We have a Fact Sheet on Botulism which provides a bit of information – http://www.wildlifehealth.org.au/AWHN_Admin/ManageWebsite/FactSheets/UploadedFiles/118/Botulism%20-%20Diagnosing%20(Birds)%2016%20Jan%202008%20(1.0).pdf . I suspect the epidemiology of botulism is complex and may present differently dependant on environmental factors and bird feeding patterns. However based on some of the literature and certainly not a comprehensive review, the grebes may not be feeding on substrate / fish affected by the toxin. Based on the UGSG NWHC Chapter in Avian disease on Botulism – http://www.nwhc.usgs.gov/publications/field_manual/chapter_38.pdf ) Plus the attached may be of interest.
It sounds as if this has previously been reported and the event investigated. The person to report to would be the Wildlife Coordinator in the Northern Territory, Cathy Shilton. She is a veterinary pathologist and may have much better knowledge regarding why certain species are affected too.
Cathy’s contact details are: Dept of Business, Industry and Resource Development Berrimah Vet Laboratories GPO Box 3000 Darwin, NT 0801 Cathy.shilton@nt.gov.au W: 08 8999 2122
For the most recent List of Wildlife Coordinator’s Contact Details for reporting wildlife mortality events follow the link: http://www.wildlifehealth.org.au/AWHN/ProgramsProjects/Programs.aspx and click on Wildlife coordinators (General surveillance). http://www.wildlifehealth.org.au/AWHN/ProgramsProjects/Programs.aspx?id=9
There’s also a paper I can send you if you want it:
Rocke, T. E. 2006. The global importance of avian botulism. Waterbirds around the world. Eds. G.C. Boere, C.A. Galbraith & D.A. Stroud. The Stationery Office, Edinburgh, UK. pp. 422-426.
Cheers, James
James O’Connor | Head of Research james.oconnor@birdlife.org.au BirdLife Australia, Suite 2-05, 60 Leicester St, Carlton VIC 3053 Tel: (+61 3) 9347 0757 | Fax: (+61 3) 9347 9323
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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
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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