Newsletter of the AUSTRALIAN PLATYPUS CONSERVANCY
ISSUE 31 - October 2005
WATCH OUT FOR WATER-RATS
Shaped for life in the water, the Australian water-rat (a.k.a. Hydromys
chrysogaster or rakali) resembles a small otter more than a standard barn
rat. Like otters, water-rats are
covered with a dense coat of water-repellant (and hence lustrous) dark fur,
rely on broad and partially webbed hind feet to propel themselves through the
water, and have a stream-lined body and blunt muzzle.
The water-rat is nearly as large as a platypus, measuring up to 40
cm in body length with a slightly shorter tail. The two species will make use of each other’s burrows and enjoy
many of the same foods, including large aquatic insects, yabbies and freshwater
shrimps. It is also possible that
water-rats (which, unlike the platypus, are equipped with a sharp set of teeth)
may sometimes prey on young platypus, particularly in the juveniles’ first few
months of development.
Water-rats and platypus look enough alike that the two animals may
be misidentified when seen swimming in the water—at least until the head or
tail are clearly observed. In place of
a bill, the water-rat’s muzzle ends in a luxuriant growth of whiskers. While thick by rodent standards, a water-rat’s
tail is much narrower than that of a platypus—and ends in a distinctive white
tip.
In general terms, the water-rat’s distribution is known to overlap
that of the platypus in both mainland Australia and Tasmania, and the two
species demonstrably coexist in many catchments. At the same time, surprisingly little is known about the true
status of water-rats in nearly all parts of their range.
Like the platypus, water-rats are quite difficult to census using
conventional wildlife live-trapping techniques. Although water-rats can in theory be captured using standard wire
mesh cage traps (set at the water’s edge and baited with fresh or tinned fish),
capture rates tend to be discouragingly low.
This probably reflects the fact that water-rats are reasonably
intelligent (and hence naturally cautious) animals that spend most of their
time foraging in the water rather than on the banks.
Alternatively, water-rats can be detained in nets placed in the
water. However, these must be set with
due regard for the fact that water-rats are air-breathing animals. As well, the water-rat’s formidable
dentition is extremely efficient at chewing through mesh netting!
Anecdotal accounts from farmers and anglers suggest that water-rat
populations have declined (or in some cases disappeared) from many streams and
rivers in recent decades.
In response to this situation, the Conservancy plans to expand its
research activities to learn more about the current status and distribution of
water-rats. The primary aim will then
be to identify problems that are having an impact on this attractive native
mammal. At the same time, the work will
help to clarify the ecological relationship between platypus and Hydromys.
To achieve these ends, the APC is
launching a community-based monitoring program for the Australian water-rat
(using the highly effective Platypus Care project as a model). This will be supported by a publicity
campaign to raise public awareness of this ‘dinky-di’ rodent. In addition, the Conservancy plans to increase water-rat live-trapping studies
along selected waterways, to complement platypus survey efforts.
PLATYPUS MOVE WITH THE TIMES
Platypus are highly mobile animals—one adult male radio-tracked
along the Yarra River in 1996 was found to travel over 10 kilometres in a
single night—and rivers and streams form natural highways. Accordingly, it would not be too surprising
if platypus regularly move substantial distances along a waterway when this is advantageous to the animals.
The results of live-trapping surveys conducted by the Conservancy along the Mackenzie River
in western Victoria suggest that just such a pattern may prevail in that area,
possibly in response to the severe drought which has gripped the region for the
past eight years.
The Mackenzie River arises in the mountainous terrain of Grampians
National Park and flows in a generally northward direction towards its original
natural confluence with the larger Wimmera River, near the town of Horsham.
Within the park boundaries, the river’s water is impounded in
Wartook Reservoir, which was built in 1887 as part of the enormous
Wimmera-Mallee Domestic and Stock Water Supply System. The presence of the reservoir ensures that
flow is maintained reliably through summer in the upper reaches of the Mackenzie
(for a distance of 10 km or so), but not necessarily farther downstream (see
also Ripples No. 21).
Live-trapping surveys carried out by the APC in 1997 (in
co-operation with Earthwatch and the Project Platypus Landcare coalition)
showed that the Mackenzie system still supports platypus, though not in high
numbers: just three animals were recorded in the one night of trapping effort
(sampling 25 km of river channel).
Since 2000, four additional surveys have been commissioned by the
Wimmera CMA (Catchment Management Authority) to provide more reliable baseline
information on the status of the Mackenzie River platypus population.
One important
finding to emerge from this work is that the Mackenzie River is estimated to
support in the order of 20-30 resident platypus, making it the second largest
population identified in the Wimmera River system as a whole. (The only larger population—found in the
Wimmera River proper upstream of Crowlands township—has been calculated to
include around 80 animals based mainly on surveys undertaken in 1997 and 1998.)
Both the percentage of trapping sites
where platypus were captured and the average number of platypus captured per
site remained unchanged when live-trapping results obtained along the Mackenzie
River in 2001/2002 were compared with those obtained three year later, in
2004/2005.
Accordingly, it is reasonable to conclude
that the number of platypus occupying the waterway did not decline
significantly in the intervening (and very dry) years, despite the fact that
the platypus is a highly water-dependent species.
This population’s ability to withstand a
long period of drought may partly rely on the fact that platypus are relatively
long-lived animals, which can survive ten years or more in the wild. Hence, adults may be able to outlast several
consecutive years of poor environmental conditions even if few or no juveniles
are weaned successfully over the period.
In addition, it was found that platypus
capture rates were much higher in the Mackenzie’s upper reaches in autumn than
in spring, nearly tripling in the case of sites located in Grampians National
Park and doubling in the case of non-park sites located within about a
kilometre of the park boundary. At the
same time, capture rates fell dramatically from spring to autumn at sites
located in the river’s much drier lower reaches.
The most obvious explanation is that—at
least in years characterised by drought—suitable platypus habitats are much
more widely available in spring than in autumn along the Mackenzie. In other words, the population is dispersed
along the length of the river in spring but becomes concentrated at sites
retaining adequate water as the summer progresses.
From the viewpoint of platypus
conservation, the seasonal concentration of most (or possibly all) of the
Mackenzie’s platypus in the upper catchment will increase the adverse impact of
any threats to the animals in this area—for example, if folding “opera house”
nets (which can very effectively drown platypus) are set illegally by poachers
or park visitors to catch crayfish.
Conversely, any actions that can be taken to increase the size or productivity of the refuge habitats currently occupied by platypus at the driest time of the year—or create additional drought-proof refuges farther downstream—are expected to be particularly worthwhile in terms of contributing to local platypus survival.
Did You Know That....
In 1799, the platypus was
first described by a British scientist, Dr George Shaw. His initial reaction to this original
specimen was that it was an elaborate hoax.
He even took a pair of scissors to the pelt, expecting to find stitches
attaching the bill to the skin.
QUEENSLAND PLATYPUS CARE
In late 2002, the Australian Platypus Conservancy launched Platypus
Care, a program to map where platypus occur based on community sightings of
the animals.
The initial focus of Platypus Care has been on waterways in
Victoria, reflecting the fact that the project was primarily funded by the
State Government of Victoria, Melbourne Water and most of the state’s Catchment
Management Authorities. However, many
sightings reports have been collected from other parts of Australia and the
intention has always been to see Platypus Care established in other
states.
In keeping with this aim, the Wildlife Preservation Society of
Queensland and the APC have been working collaboratively to develop a
Queensland Platypus Care program.
WPSQ has now created a platypus sightings database for the state,
drawn from a variety of pre-existing sources, and is starting to collect new
sightings reports. Several pilot
community monitoring sessions have also been conducted along Moggill and
Enoggera Creeks in Brisbane. A
multimedia DVD kit is being produced, drawing heavily on text from the APC
website, in order to highlight threats to the platypus, suggest platypus
conservation actions and provide hints on platypus monitoring.
Further information on Platypus Care in Queensland can be
obtained from the WPSQ website (www.wildlife.org.au) or by contacting the
Society’s Wildlife Projects Officer.
Platypus
sightings can also be reported on-line via the APC website
(www.platypus.asn.au). All Queensland
reports are shared with WPSQ.
PLATYPUS BOOK FOR YOUNG READERS
Children aged 8 to 11 can learn about platypus biology, the
importance of protecting stream habitats, and APC research in the 32-page book There
Are Platypuses in Our Creek. You
can buy an autographed copy directly from the authors for $10 (including
p&p). Make cheques payable to Alan
Lane and Virginia King, P.O. Box 388, Blackheath NSW 2785 and include the name
of the young reader. All royalties from
There Are Platypuses in Our Creek help to support the work of the
Conservancy.
WATER-RAT CARD
Reflecting the APC’s increased commitment to studying the
Australian water-rat (see page 1), the Conservancy has just produced a new
greetings card featuring this beautiful native rodent.
Illustrations are by leading Canberra-based wildlife artist Peter Marsack. Printing has been generously undertaken by Stradbroke Printing of Somerton, Victoria. The water-rat cards can be ordered from the APC at $12.00 per pack of 10, including envelopes (plus $3.00 for overseas orders).