The term “water rat” is commonly used globally to describe various aquatic rodent species, but in Australia, it refers to a specific native mammal: the Rakali. Formally known as Hydromys chrysogaster, the Rakali is biologically distinct from the invasive species often associated with the word “rat.” This specialized creature plays an important ecological role in Australia’s aquatic ecosystems, and understanding its true identity prevents confusion with common pests.
Defining the True Water Rat
The Australian Water Rat, or Rakali, is scientifically classified as Hydromys chrysogaster. This species is one of Australia’s largest native rodents, with adults typically reaching a body length of 23 to 37 centimeters and weighing between 340 and 1,275 grams. Rakali is the preferred indigenous name, adopted from the Ngarrindjeri people.
The species is widely distributed across the Australian mainland, Tasmania, and New Guinea, found near permanent bodies of fresh or brackish water. Rakali are classified as a species of Least Concern, indicating a stable population across their broad range. They play a significant role as native semi-aquatic carnivores, sharing this ecological niche with the platypus.
Unique Physical Adaptations
The Rakali possesses several morphological traits that enable it to thrive in its aquatic environment. Its body is elongated and streamlined, which helps reduce drag while gliding through the water. The coat consists of dense, water-repellent fur that traps a layer of air close to the skin for insulation and buoyancy.
The hind feet are wide and partially webbed, providing the necessary propulsive force for swimming and acceleration when chasing prey underwater. A long, thick, and muscular tail acts as a powerful rudder, enabling rapid changes in direction during aquatic maneuvers. The tail often has a distinct white tip, which is a useful identifying feature.
The small ears can be folded flat against the head to prevent water from entering during dives, contributing to the streamlined shape. The muzzle is broad and blunt, furnished with a dense array of long, sensitive whiskers. These whiskers help the nocturnal animal to sense and forage for food in turbid or dark waters.
Diet, Hunting, and Behavior
The Rakali is a nocturnal and opportunistic predator with a carnivorous diet that sets it apart from many other rodents. Its preferred prey includes aquatic organisms such as crustaceans, small fish, mussels, and water bugs. The diet can also extend to frogs, birds’ eggs, and small water birds.
Hunting techniques involve diving and ambushing prey, utilizing specialized physical features for speed and maneuverability. After a successful hunt, the Rakali often carries its catch to a favored flat feeding platform, such as a log or rock, before consuming it. Piles of discarded clam shells and crayfish claws often mark these dining spots.
A remarkable aspect of the Rakali’s feeding behavior is its ability to consume the highly toxic Cane Toad, an invasive Australian pest. The Rakali has been observed to flip the toad onto its back and make a precise incision to remove the heart and liver while avoiding the toad’s poisonous parotoid glands. They establish their homes in burrows dug into the banks of rivers, lakes, and estuaries.
Distinguishing Water Rats from Common Pests
The native Rakali is frequently confused with invasive species like the Black Rat (Rattus rattus) or the Norway Rat (Rattus norvegicus). A key distinction is size, as the Rakali is significantly larger, weighing many times more than the average pest rat. The Rakali’s body can exceed 35 centimeters, while pest species are much smaller.
A clear visual difference is found in the tail; the Rakali possesses a thick, well-furred, and muscular tail, often ending in a characteristic white tip. Invasive rats, by contrast, have thin, hairless, and scaly tails. The Rakali also has a broader face and a coat that is dark above and lighter on the belly, ranging from white to orange.
The Rakali is a semi-aquatic specialist confined to areas near water, whereas pest rats are terrestrial and found in a wide variety of human-dominated habitats. The Rakali is a protected native Australian mammal, not a pest, and its presence is often an indicator of a healthy aquatic ecosystem.