Peter, given that climate change is already altering the migration
patterns of short - medium distance migrants in the northern
hemisphere, is it possible that OBPs might be able to consistently
overwinter in Tasmania?
Regards, Laurie.
On 05/05/2010, at 1:39 PM, Peter Menkhorst wrote:
folks
as Chair of the OBP Recovery Team I too have been astonished at the
lack of response to our press release of a couple of weeks back
[issued via the Commonwealth Minister's office] from both the
mainstream media and the birding community. I thank Sean Dooley for
being something of a lone voice on behalf of the bird. However, I
would like to add some further information that could not be
included in the press release, but is freely available from the
recovery team, and to correct a couple of false statements in Sean's
newspaper article.
1. The grim prognosis for the wild population is due to a decline in
the number of females that have attempted to breed during the past
few summers, although those pairs that have bred have achieved more
than adequate success rates for an individual nest - > 4 fledglings
per active nest.
2. When combined with the rather short breeding life-span of OBPs [<
6 years, probably only 3-5 years in most cases], a couple of years
of low recruitment can have a big impact on a small population. Our
population modelling shows the population continuing in a steep
decline and hitting zero by 2016. Note that this is only a
prediction, but we have a fair bit of faith in the data and the
analysis, and therefore must take a precautionary approach and
assume that it is accurate.
3. On the other hand, our information about survival rates, derived
from sightings of colour-banded birds [reported to us by our
volunteer monitors at Melaleuca and other birders who come across
OBPs], indicates that there is no problem there. In other words,
there is not a critical cause of mortality that is driving the
population down, for example wind farms or lights on the squid
fishing fleet in Bass Strait, or even starvation as suggested by
Sean in the press. Rather, the rate of recruitment to the breeding
population is not adequate to overcome the rate at which older birds
are leaving the breeding population.
This suggests that there could be a problem with habitat quality
that is constraining the ability of birds to achieve adequate
condition to successfully produce eggs. This could be a lack of a
quality diet on the mainland during winter, or on the breeding
grounds in the 4-6 weeks that birds have there before egg-laying in
December. Interestingly, in the captive population, where the birds
are given a carefully managed diet, the breeding participation rate
is high.
4. Sean's hypothesis about the role of drought in reducing habitat
quality is quite plausible and the recovery team has considered that
possibility for some years. What can the recovery team do about
drought/climate change? Perhaps the only action available to us is
to provide supplementary food to wintering birds to possibly improve
their condition. This we plan to do. Likewise, we will provide a
boost diet for the birds when they arrive back at the breeding
grounds, in an attempt to get more females into breeding condition.
5. All of this greatly increases the importance of our captive
population [currently 167 birds] as insurance against the demise of
the wild population. We need to do a bit of work to ensure that the
captive population is as good an insurance policy as it can be. This
includes improving its genetic base by taking more founder
individuals from the wild. This can be achieved with minimal impact
on the wild population by removing a single young from a number of
nests [yet to be finally determined] over the next couple of years.
If we can locate unbanded juveniles on the mainland we may also
attempt to catch those because unbanded birds come from a different
breeding population to the main Melaleuca group, where all chicks
are banded in the nest, and therefore may contain genetic material
that is not currently represented in the captive population. We are
not proposing to take adults, as stated by Sean in the press. Note
also that OBPs rarely if ever successfully rear a second clutch in
the wild, so we are not proposing to remove entire clutches to
captivity [Sean suggested this as a better option].
6. We do not share Sean's pessimism about the ability of captive-
bred and released birds to successfully complete the migration
cycle. We already have numerous examples of them doing exactly that,
including situations where the released birds did not have the
benefit of wild birds to show them the way, if indeed that ever
happens. Successful migrations by captive-bred birds include birds
released at 2 separate sites in southwest Tasmania in spring and
birds released on the mainland during winter.
For these and other reasons, the OBP recovery team sees captive-
breeding and release as being a critical component of future
programs to conserve this species as a component of Australia's
wildlife. That does not mean that we are abandoning the wild
population. In fact we will redouble our efforts to improve the
quality of habitat, in Tasmania and on the mainland.
sorry for the long rant - but these are not simple matters and I
wanted to provide adequate information to allow a better
understanding of the situation and the reasons for the plan of
action that the Commonwealth and State Governments are now supporting.
Peter Menkhorst
www.birding-aus.org
birding-aus.blogspot.com
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