Rabe, Water-rat
The rakali (Hydromys chrysogaster) is an Australian native rodent first described in 1804. Having adapted to and colonized a unique niche of a semiaquatic and nocturnal lifestyle, this rakali lives in burrows on the banks of rivers, lakes and estuaries and feeds on a wide range of aquatic prey. These animals were hunted for their soft fur and considered a nuisance animal; numbers were under threat until a protection order in 1938.
Rakali have a flattened head, partly webbed hind feet and water-repellent fur that also offers insulation. Their waterproof thick coat varies from extremely dark fur, black to slate grey on their back and white to orange underneath. The thick dark tail is an identifying feature with its white tip. Their coat changes through the process of moulting, according to sex. Males and females moult in autumn and summer, and females additionally in spring. Moulting is conditional to temperature, reproductive condition, adrenal weight, health and social interaction. The hind feet are wide and partially webbed, and the broad face, flattened head and long whiskers are all distinguishing features.
Rakali are found in Australia, New Guinea, and offshore islands. They live near permanent water in a diverse range of habitats that varies from fresh slow-moving streams, brackish inland lakes, and creeks to wetlands, rivers, estuaries, sheltered marine bays, and beaches on coastlines.
Rakali are active during the night. Their home range typically comprises 1-4 km of waterways and they can travel a distance of between 200 m to a kilometer in a night when foraging. They search for their food at dusk, partly by sight when in the water and hunting prey on the water's edge returning to a favorite feeding place where evidence of previous catches can be seen. They can be found swimming and feeding in the early morning and evening. Rakali do not tolerate low temperatures well, so in winter they prefer to hunt terrestrial prey. They also spend long periods in the warmth of the burrow. These well-adapted semi-aquatic and territorial creatures may become very aggressive in high-density populations as they are mostly solitary. Fighting is common, leading to scarred tails from being bitten during fighting amongst both adult males and females.
Rakali are carnivores. They feed on a variety of aquatic animals including fish, crustaceans, shellfish, small birds, eggs, mammals, frogs, and reptiles. In winter, when resources are limited, they will also take plants.
Rakali breed from late winter to early spring. Under good seasonal conditions, these solitary animals come together with their mate and may produce several litters (if young are removed will reproduce again within two months), but separate on the birth of the young. Rakali usually nest in burrows which they construct in river banks but they may also build their nests within sunken logs and reeds, in areas surrounded by roots and dense riparian vegetation for cover from predators. Females typically produce litters of 4 to 5 young after the gestation period that lasts about 34 days. The young are born blind but they grow quickly and are usually independent after about 4 weeks. Reproductive maturity develops at around 12 months of age and females are able to breed until they are 3.5 years old.
Hunted for their soft fur and considered a nuisance animal, rakali were under threat until a protection order in 1938. They were still under destruction permits from 1938 to 1957 due to the alleged destruction of irrigation banks and the destruction of fishing nets. Although nationwide today the rakali populations appear stable there are individual populations facing a significant threat. Near threatened in Western Australia's wheat belt, urbanization, salinization, waterway degradation, and pollution have all attributed to this status change. In the Victorian Lake Wellington, Lake Victoria, and Lake Tyers region numbers have declined in the past fifty years attributed to commercial eel-fishing, predation, loss of habitat due to commercial development, and poisoning from baiting programs placing this species at risk.
According to IUCN, the rakali is locally common throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List.
