Rakali (Common Water-rat)

## About

A rakali hiding in the entrance to it's burrow.

## Background Information

### Alternate Name(s)

Rabe, Common water-rat, Australian water-rat, Golden-bellied water-rat, Native water-rat, Beaver rat, Australian otter, (Unofficial)

## Classification

### Species

H. chrysogaster

The rakali ***(Hydromys chrysogaster)*** also often known as the common water-rat, is a rodent species that inhabits the river banks and coasts of Australia, as well as Papua New Guinea and Indonesia. Rakali have round bodies, long faces and snouts, small black eyes and short front limbs. They have blackish-brown fur that darkens on the tail and transitions to an orange or gold colour on its underbelly, giving it the alternate name; golden-bellied water-rat. The face is narrow and the end of the snout is tipped with many whiskers. Due to the species' semi-aquatic lifestyle, the hind feet are wide and have webbed toes, similarly to that of a duck. The tail has a noticeable white tip and acts as a rudder while swimming. The rakali can reach 23.1-37cm (9.1-14.6in) in body, with its tail reaching 24.2-34.5cm (9.5-13.6in). They can weigh up to 340-1,275g (0.750-2.811lbs). It is thought that the males are larger than the females however, the size typically remain constant between the two sexes.

## Diet

Rakali are opportunistic carnivores, consuming a wide variety of animal matter. As a semi-aquatic species, the rakali often preys upon, crustaceans (such as yabbies ***(Cherax destructor)***), molluscs and even fish. They have also been observed eating; aquatic insect species, amphibians, house mice ***(Mus musculus)***, juvenile waterfowl and waterfowl eggs, ducks, poultry birds and turtles. It has also been reported that rakali attack bat and swan species. The muscular jaws and strong incisors of the rakali are used to break open and eat mussels. The rakali has also been known to kill and eat cane toads ***(Rhinella marina)***, a poisonous invasive species that has vastly damaged the Australian ecosystem. Rakali often stock-pile food in a preferred area of their territory, typically their nest or another platform. Evidence has shown that rakali may even target platypuses ***(Ornithorhynchus anatinus)***, though extremely rarely. One account has been recorded of this interaction, detailing a rakali that attacked a platypus for an unknown reason. Whilst the platypus attempted to escape, it eventually retaliated, killing the rakali by drowning it.

## Conservation Status

The rakali is listed as a least concern species by the IUCN and it faces few major threats. The rakali may be threatened by subterranean mining activity in New Guinea, as these practices create pollution. Due to the increase in salinity caused by agricultural activities in southwestern Western Australia, populations have declined.

## Range and Population

The rakali inhabits much of New Guinea and its surrounding islands, as well as every Australian state and territory, including Tasmania. It occurs in wetland environments, like marshes and rivers, most commonly in forested or coastal regions. The rakali has also been known to be able to live in saltwater environments, often being found abundant in neritic areas, specifically around shallow waters and peers. the rakali can also easily inhabit urban areas, often being found in the concrete-lined pools or lakes of botanical gardens or parks. Though the species is overall, incredibly adaptive and opportunistic, it has become regionally extinct in the Montebello islands of Western Australia, due to an abundance of domestic cats ***(Felis catus)*** and other invasive predators. The rakali is also restricted from the colder areas of its range due to not having waterproof fur, which leaves the species vulnerable to low temperatures and conditions such as hypothermia. The rakali has combated this weakness, by evolving an interscapular pad of brown fat, which insulates the heart and allows warm blood to flow to essential areas, such as the spinal cord. Evidence has also suggested that rakalis may be fewer in numbers in areas which platypuses inhabit, as the species' ranges overlap. This may suggest that platypuses kill rakali. The exact population of the rakali and its status are unknown.

## Behaviour

The rakali is a nocturnal species that is most active at night. Rakali are fossorial and construct burrows, where typically only one individual -or a female and her young- will reside. They will construct burrows of river or lake banks, hiding the entrance typically under a log, or piece of vegetation. Burrows may even have two entrances and multiple chambers, which can reach 20cm (7.8in) in height. Rakali breed throughout the spring and summer (September-February). Females go through an estrous cycle that lasts 11 days and their gestation lasts 35. As an iteroparous species, the rakali can re-enter estrous after birthing a litter and can have a new litter just 35 days after their first, of which at this point, would be completely independent from their mother. A single female may have up to 2 or 3 litters in a single season. The pups are born blind and are lighter in colour compared to their parents. They will reach their adult size after reaching age 2.

### Relationship with Humans

The name "*rakali*", stems from Aboriginal origin and was adopted by Environment Australia, in order to give the species a better public reputation, as the name water-rat instills a negative opinion towards the species. The name "native" water-rat has also been used to differentiate the rakali from harmful invasive species and deter hunting of the species. Rakali have been also influential in agricultural areas, eating parasitic snails and preying on yabbies and rodents that destroy irrigation systems. Rakali have also been detrimental to human settlements, disrupting river banks and water control structures such as dams.

## In Captivity

The rakali has not only been previously housed in Australian zoos, such as Healesville Sanctuary and Taronga Zoo, but it has also been popular in Europe, in zoos such as London Zoo, Zoo Antwerpen, Belgium and ZOO Plzen, Czechia. Despite the rakali's specialised lifestyle, the species has been successful in captivity, even outside of Australia.

## Sources

* IUCN Red List of Threatened Species - https://www.iucnredlist.org/species/10310/115097054
* Golden-bellied Water-rat | Animal Diversity Web, University of Michigan Museum of Zoology - https://animaldiversity.org/accounts/Hydromys\_chrysogaster/
* Rakali | Wikipedia - https://en.wikipedia.org/wiki/Rakali
* Charismatic rakali (native water rat) talk on 1 March 2018 | Connecting Country - https://connectingcountry.org.au/charismatic-rakali-native-water-rat-talk-on-1-march-2018/
* Fight to the death: image of platypus and rakali stoush shocks and surprises | Australian Geographic -https://www.australiangeographic.com.au/topics/wildlife/2019/11/fight-to-the-death-image-of-platypus-and-rakali-stoush-shocks-and-surprises/
* Beaver Rat | ZOOINSTITUTES - https://zooinstitutes.com/animals/beaver-rat-875/