Should Blue-billed Duck be listed as at least Near Threatened?

[Peter Woodall <>]

At 02:27 PM 28/05/2003 +1000, you wrote:
> wrote:
> > On this forum Lawrie Conole highlights the number of Blue-billed Duck currently (or at least in late 2002) at Werribee.  He also suggests that having 10 000 Blue-billed Duck (greater than the current population estimate for eastern Australia) all at one location is dreadful risk management by the taxon in question. 
>
> > A very good point of course - all your eggs in one basket and all that.  What are the risks for these Blue-billed Duck?  A huge hailstorm perhaps?  Thinking more laterally however, is there any risk of the ducks picking something up from this water (partially or completely treated as the case might be) that might have an adverse impact on the population?  I guess the potential for something being passed from primates to ducks is pretty remote but is it possible?  Sewage treatment plants are great places to see ducks but are they great places for ducks? 
>
> There are no recorded instances that I'm aware of  for any kind of toxic spike knocking off large numbers of birds at Werribee, but this strikes me as a possibility.  Maybe the dilution factor from Melbourne's enormous discharge of wastewater renders this risk negligible?  Many of the ponds were mint green earlier this year with blue-green algae, but birds were merrily surfing about in that too.
>
> > Personally I have no idea.  Anyone out there have any expertise in this area? 
>
> I'm with you David - please forward all speculation (idle or otherwise) for our consideration or edification.
>
> L.
>
>
> -- 
> =================================
> Lawrie Conole


Well If you want pure speculation, I happy to give some.

A possible "toxic spike" that can knock off large numbers of waterbirds is botulism.
The organism, Clostridium botulinum, seems quite widespread  but it needs particular
(anaerobic) conditions to grow and release its toxin.

In North America it causes widespread deaths of thousands of waterbirds every year but here it
seems comparatively rare.  However, in the early 1980's I investigated and reported on 
outbreaks at Seven-mile Lagoon, near Atkinsons Dam in the Brisbane Valley that killed
many hundreds of ducks,and many Black Swans (Aus Wildl Res 9:533, 1982). 
[NB in this study the "scientist" killed no birds but nature killed over 1 000]
In this location, the previously drying lagoon had filled, flooding the surrounding vegetation
and causing anaerobic conditions in warm weather.

Since then there have been occasional reports, usually affecting just a few birds.  
For example, each year it is not uncommon for one or two ducks
on the lake on the UQ St Lucia campus, Brisbane, to show symptoms - often fatal.

Why botulism isn't more widespread in Australia, like the American situation, I don;t
know. The conditions often seem ideal for it, or is it never investigated and reported?

Cheers

Peter Woodall


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