Hi Peter -
At 12:46 PM 12/04/00 +1000, you wrote:
>So while your option 3. sounds very scientific and considered (and keeps a
lot
>of biologists employed) I submit that there are occasions when you need to
take
>direct and immediate action, option 2, using, of course, the best biological
>knowledge that has been gathered previously.
I agree that immediate action needs to be taken sometimes. When you get a
House Crow hopping ship at Fremantle, or a fox stowaway on a ferry to
Tasmania, you act immediately - although the act may be (ideally should be)
part of the implementation of a previously developed strategy.
In the recent case of the Silver Gulls and Banded Stilts at Lake Eyre, it
was not completely clear at the outset that the Silver Gulls would prey on
the Banded Stilts' eggs and chicks to the extent that they did. A previous
Banded Stilt breeding event (at Lake Torrens in South Australia some 10?
years ago) suffered some Silver Gull predation, especially later on after
the early Stilt breeders successfully hatched their chicks and safely
escorted them to the water where they werer relatively safe. The later
breeders suffered much heavier predation - increasing to 100% as Gull
numbers increased. However, it was considered a relatively successful
breeding event. So the latest, Lake Eyre, breeding attempt was an
opportunity to gather further information about predation, and the
desirability of somehow controlling the Silver Gulls (probably by killing
them - although other methods might be considered) only became apparent in
the course of the week-long study. If the Stilts attempt to breed again
(and this will presumably depend upon continuing availability of large
quantities of brine-shrimp in the Lake) then controlling the gulls would be
an option. Moreover, the information should feed back into conservation
strategy refinement for the Banded Stilt. One could also argue that
pre-emptive killing of the Silver Gulls present on the breeding island
would have been premature on the basis of existing knowledge while
forestalling the possibility of learning more about predation rates and
behaviour.
Since the two threads appear to be converging, I can also try to answer a
few of Frank O'Connnor's questions about the Lake Eyre Banded Stilts, even
though my information is far from complete and a full report from Clive
Minton on his sojourn on the island in Lake Eyre will be available shortly:
>Were the Silver Gulls breeding?
I believe so.
>Were the Red-capped Plovers breeding?
No information.
>Was there only one Banded Stilt colony?
On the island where the researchers went, yes. I do not know if there are
any BS breeding attempts happening elsewhere in the inland, but have no
information on any so far.
>Did the Banded Stilts that lost their eggs / young attempt to renest? Maybe
>somewhere else?
The study was only for a week. It is possible that renesting, there or
elsewhere, will happen.
>Did the Australian Pelicans attempt to nest this year?
I heard there were Pelicans breeding on the same island, but have no
information on numbers.
>Did any cormorants attempt to nest anywhere?
No information.
>Do Silver Gulls only predate the Banded Stilt colonies?
I imagine that SGs would prey on anything suitable, but the BS colony must
have been by far the biggest source of food around.
>Was any attempt made to determine where the Banded Stilts came from to breed?
No, although Banded Stilts are known to spend their lives, when not
breeding, along the coast - and the Lake Eyre Stilts are assumed to come
from the coastal population of SE Australia. It was the combination of the
inland rains and the flooding of Lake Eyre on one hand, and the
disappearance of Banded Stilts from their usual coastal haunts, that led to
the inference that they might be breeding and the successful search for the
breeding location. If WA Banded Stilts have also disappeared from the
coast and WA salt-lakes (such as Lake Ballard) have flooded, a search might
produce interesting results. Maybe satellite photography could detect BS
colonies.
>Similarly, where did the Silver Gulls come from?
Uncertain, although they must have come from elsewhere when the Lake
flooded and, as far as I know, the nearest large populations would be on
the coast and associated with human settlement.
>Is anyone aware that the flats near Sandfire Roadhouse (southern part of Anna
>Plains Station) 200km south of Broome in NW Western Australia have flooded
>again? I know in previous years that large numbers of Black-winged Stilts
>(1,000s) turn up there to breed, along with large numbers of Whiskered Terns,
>ducks, etc. There have been press reports of the fish that are now there
but no
>mention of the birds. Where do the Black-winged Stilts come from? Why do
>Black-winged Stilts flock to this area and not Banded Stilts, and vice
versa why
>do Banded Stilts flock to Lake Eyre, etc and not Black-winged Stilts? Is it
>fresh versus salt water?
I think it is related to fresh v salt water. Banded Stilts are strongly
associated with salt (often hypersaline) water and Black-winged with fresh.
Banded Stilts also appear to breed exclusively on flooded salt-lakes when
brine-shrimp are superabundant. A look at HANZAB (Vol.2?) should tell you
more.
If anybody has anything to add to this information, I would be interested
to see it. The Banded Stilt is a species that holds a fascination for me,
so maybe my interventionist stance regarding gull control is not wholly
unbiased.
Finally, for your information, I leave you with an extract (complete with
lurid headline) from the latest issue of the Tattler (newsletter of the
Australasian Wader Studies Group - No.23, email version, received today):
-----------------------------------
Murder at Lake Eyre
The Lake Eyre Banded Stilt colony (see article this newsletter) was
decimated when Silver Gulls took eggs or chicks from over 16 000 nests of
the 18 000 nests originally counted. When Clive Minton and other expedition
members returned to the site the number of active nests had already dropped
to 9 000. They watched in horror as the Stilt colony was reduced to 1 500
nests. Only 322 juvenile stilts survived this onslaught. It was previously
thought that Silver Gulls predated Banded Stilt colonies towards the end of
a nesting event when fewer stilts were on hand to protect their nests. This
event focuses the need for controls on the ever increasing Silver Gull
populations in southern states.
----------------------------------
Cheers,
Hugo
Hugo Phillipps
Communications Coordinator
Birds Australia
415 Riversdale Road
HAWTHORN EAST 3123, Australia
Tel: (03) 9882 2622, fax: (03) 9882 2677
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Web site: <http://www.birdsaustralia.com.au>
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