All four satellite
transmitters on Little Curlews which were sending out regular signals until
mid-May have now stopped transmitting. From elation just a few weeks ago when
five birds carrying transmitters set off from north-west Australia we are now
extremely disappointed that everything seems to have come to a complete halt.
Little Curlews Numenius minutus; Broome, Western Australia. Photo: Ric Else. |
We
were hoping (against hope) that some of the transmitters might start up again
if part of the problem has been overcast weather conditions the birds have
encountered in China, thereby causing a lack of solar recharging of the
batteries. But it is now six weeks since the last transmission and I fear that we
really have to accept that we are not going to obtain any further information
from these transmitters.
At the moment we really have no clue to the cause/s of this
sudden demise of the units. Are there possibly technical difficulties in this
batch of units, which have resulted in unusually short transmission lives
(meant to be 1 + years)? Evidence from other users of the same MTI product
(Reece Pedler and in Alaska) has not revealed any significant problems with
performance or longevity of these satellite transmitters so far. It seems hard
to believe that all birds have, almost simultaneously, been predated by animals
or captured by hunters. Perhaps the most likely cause is that the birds have
shed their transmitter harnesses. It may be significant that the timing of most
losses coincided with periods of migration when significant distances were
being traversed. It is just possible that the loss of accumulated fat used up
in these journeys allowed the harnesses to become too loose.
Little Curlew with satellite transmitter attached Broome Western Australia February 2015. Photo: Tz-Yu Liao |
We are continuing to seek comparable satellite transmitter
information from other researchers around the world, particularly those who
have used satellite transmitters on shorebirds, to help us work out what may
have gone wrong.
Whilst the disappointment of the failures is at the
forefront of our minds, we should recognise that we have still learned a great
deal about Little Curlew behaviour from these satellite transmitters over the
last three months. This includes new knowledge about: local, non-breeding,
movements in Australia; migratory departure locations in Australia; and
northward migration routes and stop over sites.
All five birds, which had transmitters put on at Anna Plains
and 80 Mile Beach in mid-February continued to roam around the grasslands of
Anna Plains station until the end of March. With them was the sole remaining
Little Curlew with a satellite transmitter from the Roebuck Plains, Broome, November
2013 deployment. This bird moved back and forth between Roebuck Plains and Anna
Plains before setting off again on this year’s northward migration (from
Roebuck Plains). One of the Anna Plains/80 Mile Beach birds, from the 2015
deployment, also moved to Roebuck Plains before northward migration. Another
one spent several weeks in the Fitzroy River estuary near Derby before its
transmitter stopped around the time the first two Little Curlew left on
migration from Anna Plains/80 Mile Beach. We therefore have strong evidence
that Little Curlew depart on northward migration from a variety of locations in
North West Australia.
Map supplied by Inka Veltheim AWSG |
All birds confirmed the migration strategy, which first
became apparent during the 2014 northward migration. Most birds stopped in the
Indonesian region (1000-2000 km) for between 1-2 weeks. Most then moved on to
some part of the Philippines for another short stop-over.
Map supplied by Inka Veltheim AWSG |
The Chinese coast was
the next destination and it was at this stage where most of the transmissions
from the Little Curlew units ceased – we had fixes from two birds, which had
reached the coast. This project has shown that Little Curlew seem to be
different to most other wader species leaving NWA on northward migration. Most
other species put on large quantities of fat (up to 100% addition to their
fat-free weight) and many complete their journey (5000-6000 kilometres) to the
Chinese coast (including the Yellow Sea) in a non-stop flight. Little Curlew on
the other hand seem to put on much less weight (40-60%) before departure and
make several stops on the journey before reaching China. Late departure and
several stop overs prior to reaching China also correlates well with (maybe a consequence
of?) Little Curlew not completing their wing-moult until early March, whereas
most other waders complete it in January or early in February. Energy resources
are not normally devoted to weight accumulation until the main moult of the
primary feathers is complete.
At this stage, it appears likely that there will be no
further blogs this year concerning the movements of Little Curlew carrying
satellite transmitters.
We will be carrying out a thorough investigation to try to
be sure that the performance of satellite transmitters we deploy in the future
is much improved. This will include exploring different harness design options.
Map supplied by Inka Veltheim AWSG |
Meanwhile thanks for everyone’s interest and support.
I've been thinking about this situation and one possibility may be related to Chinese restrictions in satellite law transmissions. Depending on the satellite used, it may not be registered in the China therefore not being allowed to capture any signal there.
ReplyDeleteI'm working with GSM (OK, is not satellite but uses the same thinking for laws) in Brazil and had to ask for special permits so my devices could work in their territory.
An interesting thought but it would mean that things will have changed since the last northerly migration where all the birds transmitters were picked up as they crossed China. A change in Chinese policy though is not beyond the realms of possibility. thanks for sharing this thought Bianca.
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