Scientific name: Hydromys chrysogaster - Golden bellied water rat
Pronunciation: hi-dro-mis, (hydor, water and mys, a rat)
kry-soh-gas-ter (chryso, golden and gaster, belly)
Common Name: Rakali (RAH-KAH-LEE)
The River Conservation Society is undertaking research into the wild population of the Rakali, or water rat (Hydromys chrysogaster), in the Avon River environs. This animal is well adapted to an aquatic life and is one of Australia’s largest rodents. The Rakali’s ancestors are believed to have arrived in Australia from Papua New Guinea approximately 5 – 10 million years ago.
The R.C.S. currently uses the name “Rakali” for these native rodents. This common name is now widely used across Australia and was adopted to try to lift the water rats profile by removing the negative connotations associated with the word “rat”. Rakali are known as Moyitj by the local Ballardong Noongar people.
Rakali have adapted to living with humans, unfortunately to its own detriment, due to being hunted to the point of extinction for its fur before becoming a protected species . Their survival, especially in the highly altered riverine environment of the Wheatbelt, is threatened by habitat alteration both past and present, a decline in water quality due to flood mitigation and urbanisation, and predation by introduced animals.
It is a distinctive rodent well adapted to an aquatic existence. A large animal between 23 – 40 cm in length (not including tail) with large webbed hind feet and a waterproof fur coat. It can be identified relatively easily by its large body length, long and thick fur covered tail with a white tip at the end and webbed hind feet.
The Rakali’s diet consists of large insects, fish and crustaceans and can even include frogs, small lizards, and small mammals. Once it catches its prey it usually carries it back to a regular feeding site (midden) to consume it. Rakali are strong swimmers, allowing them to pursue their prey both on the surface and under water.
Its habitat is usually near permanent bodies of fresh or brackish water and it lives in burrows alongside riverbanks. It has been known to nest in hollow logs along riverbanks and on the edges of pools.
The Rakali is most active around sunset and sunrise but can be seen foraging during the day. Males tend to be solitary animals and are very territorial. They will defend their patch vigorously against other males which intrude into their area.
Rakali are an important indicator of aquatic ecosystem health. The purpose of the project being undertaken by the River Conservation Society is to establish if there is a breeding population of Hydromys chrysogaster still active in the region, are the animals present a unique sub species of Hydromys, specially adapted to this inland area, are they under serious threat of extinction in the Avon River system.
Update November 2022
Rakali, Riparian & River Health Project
With our funding in place we were eager to get started. In late July 2022 R.C.S. members commenced river pool surveys. Our enthusiasm was quickly dampened by rising flood waters and we had to wait for the river flow to drop enough to safely continue these surveys.
In late October following the flood, Gwambygine Pool was surveyed by kayak. We were very excited to discover several sets of Rakali tracks and a couple of feeding middens containing gilgie (Cherax quinquecarinatus) claws and shells. This is an encouraging sign as gilgies are an important source of Rakali food and a healthy gilgie population could be crucial to sustaining or possible growing the Rakali population in Gwambygine Pool.
In early November we kayaked down stream from Wilberforce Crossing to Wilberforce Pool which has not previously been surveyed for Rakali presence by the R.C.S. This large, deep, permanent pool is approx. 1km long and 40-50 metres wide and has potentially good habitat for Rakali. A set of large gilgie claws were found in a braided section of the river just upstream of the pool. Several footprints that strongly resembled Rakali tracks were observed, but it was not possible to make a positive identification of these tracks.
Several days later a large lagoon just upstream of Wilberforce Crossing was surveyed by kayak and by a land-based inspection of parts of the riverbank. This permanent pool is about 200m long and 20-30m wide with large old Swamp Paperbark trees (Melaleuca rhaphiophylla) overhanging the water on the right-hand bank, providing good shelter and habitat. Fresh Rakali footprints and several feeding middens were found, including a large, freshly eaten, freshwater crayfish species. This was later confirmed by the Department of Water and Environmental Regulation (DWER) to be a gilgie displaying a typical Rakali feeding pattern.
Update December 2021
We are thrilled to announce our “Rakali, Riparian & River Health Project” will be funded through a grant from the State Natural Resource Management Program WA. Our three year project will, amongst other things, monitor and report on the endangered Wheatbelt Rakali. The project is expected to commence in early 2022, keep up to date with our progress by reading our project updates under the “Projects” tab on our Homepage and following us on Facebook and Instagram.
Update May 2019
Bland’s Pool is being surveyed with three wildlife cameras deployed. Rakali were recorded at Gwambygine Pool with three photos taken of two separate animals. Footage was captured at dawn and dusk on three consecutive days indicating healthy water rat activity. Gwambygine Pool is full and has started flowing, Dale River catchment rainfall events are contributing to this. The video below shows two Rakali in another Avon River pool. One was very shy and kept away from us, you can see it swim across the pool at the beginning of the video, the other one swims down the right hand bank ending up very close to us, video was taken at approx 4:45pm, so lucky to see them!
Update May 2018
The last few months have been very busy with our water rat surveys on the Avon River and the results have been very encouraging. Thankfully the weather has been very kind to us with participants surveying for water rat sign both on the water and along the riverbanks. Very welcome relief on hot days paddling around the pools.
Hydromys has been very busy this year and it is looking as if we have an active population of water rats (and quite possibly a breeding population) living in the Avon River system and its pools within the York Shire.
The more we learn about the movements and habits of this very shy rodent the more amazed we are due to their habits and behaviours.
These rodents can cover a fair bit of ground during the night on their food foraging trips and are amazingly fast swimmers. They can also become extremely aggressive to intruding feral rodents who happen to encroach on their territory or feeding middens to scrounge a few scraps!
The River Conservation Society is undertaking research into the wild population of the Water Rat (Hydromys chrysogaster) along the Avon River environs. This animal is well adapted to an aquatic life and is one of Australia’s largest rodents.
It was thought that the native water rat had disappeared from the Avon River due to poor water quality. dwindling food sources and the filling in of permanent pools along the Avon River due to sedimentation.
Pictures taken recently by the survey team have been confirmed by the Zoological Department of the University of Western Australia as that of the native water rat (Hydromys chrysogaster) and identified as that of a mature, healthy adult, possibly female. This native rodent appears to be actively foraging at night. Images were obtained using infra-red technology located near feeding middens identified during the Society’s surveys of native water rat habitat.
This evidence provides new and interesting information concerning this native rodent’s distribution within Western Australia and is extremely important for the eastern wheat belt region of Western Australia as it was thought to have disappeared from this region in the last 10-15 years. With further research required it may well provide new insight into the genetic diversity of this species in inland regions.
The purpose of the project being undertaken by the River Conservation Society is to establish if there is a breeding population of Hydromys chrysogaster still active within the Avon River region. Should the water rat be deemed under threat then methods will be explored to increase numbers and provide habitat to help protect these native animals.
This is exciting news for River Conservation Society members, the York community and the University of Western Australia. It highlights the importance of the Avon River and the role it plays in protecting the diversity of native fauna and flora along the river and its surrounding riparian zones.