The precise causal reason may remain a mystery for now, without some specific
research, but I think the general reason is very clear. Ibis are reasonably
adaptable breeders - white ibis breed in the centre of Sydney. This species is
also a generalist feeders, even scavenging on rubbish tips. On a
macro-environmental scale, the landscape is changing considerably and since
both Ibis feed primarily in agricultural areas, it is highly likely this is the
source of change. It is unlikely that there has been a sudden increase in the
availability of nest sites!
All over the world, agricultural intensification is causing widespread decline
in common farmland species and benefit to just a few generalists, able to
exploit the types of monoculture being created for either livestock or arable.
As far as I can tell, Australia is yet to recognise the immense problem this
is. We categorically fail to track the advance of modern fertilisers and farm
practice, including the huge impact that small changes in the timing of
production can have on whole suites of species.
I notice that the Birds Australia atlas does not conclude any change in
distribution for these birds. This is hardly surprising, as they depend on some
surface moisture for feeding and would be biogeographically limited. Local
distribution and abundance however, appears to have changed. Data for the
Gippsland Lakes since 1975 seems to indicate that they were once quite uncommon
but underwent a huge expansion in the 1990s. Since then however, they have
again declined but this is mostly thought due to loss of breeding sites. I
don't think this reflects numbers of birds in the surrounding landscape which
anecdotally seems to have increased.
The impact of agriculture on Australian biodiversity is, like in every other
country of the world, a key macro-environmental problem but barely rates
mention on our conservation agenda. The increase in few birds like Ibis simply
mirror the equally substantial decreases in a large number of other species
through the loss of biodiversity and homogenisation of the landscape. In my
opinion, there is an urgent need for Birds Australia to take a look at its
atlassing methods and start to include estimates of abundance as well as
likelihood of occurrence. It could take five years to collate enough volunteer
information to make sense of these problems and it would be good to see this
happen in time to do something about it.
Regards,
Simon Mustoe.
> From: > To: ;
> ; > Subject: Re: [Birding-Aus]
> White Ibis studies in Sydney Region> Date: Wed, 16 Jan 2008 10:16:38 +1100>
> CC: ; > > On 12
> January 2008, 10 Australian White Ibis and 170 Straw-necked Ibis were > at
> the Banyan Waterhole, a remnant of the once extensive Carrum-Carrum > swamps
> SE of Melbourne. Nothing particularly remarkable about that one might > think
> unless one knows some history. 150 years ago, when Horace Wheelwright >
> frequented this swamp, he saw Ibis only once or twice and his description of
> > the bird is an amalgam of White and Straw-necked Ibis. Just when and why
> the > population exploded here on the Mornington Peninsula, I'm not sure. But
> > they've increased since I arrived in 1964 and where then there were none, >
> there is now a huge colony on Mud Islands in Port Phillip Bay.> Wheelwright
> published his experiences in 1861 in Bush Wanderings of a > Naturalist, or
> Notes on the Field Sports and Fauna of Australia Felix, now > available from
> Oxford University Press.> > Mike Carter> 30 Canadian Bay Road> Mount Eliza
|
