Rodents comprise a vast variety of species characterised by having only a single pair of continuously growing incisors in both the upper and lower jaws. There are over 2000 described species, which include such diverse species as porcupines, squirrels, cavies, beavers, and, of course, numerous species of rats and mice.
Over half of all mammals on earth are rodents.
These highly successful mammals are represented in Australia by only one of the 24 families of the order Rodentia - the Muridae (rats and mice). Further, all of these are relatively 'recent' arrivals, having entered Australia from the north no more than 15 million years ago. There are about sixty species so far described in Australia, with new species still occasionally being found.
In Tasmania, only five native rodents are found. The relatively low number of species in Tasmania is partly a reflection of the islands temperate latitude and its biogeographical isolation from mainland Australia during interglacial periods.
The five species that are native to Tasmania are:
Long-tailed mouse, Pseudomys higginsi
The long-tailed mouse is the only species of rodent endemic (restricted) to Tasmania. The species reaches about 70 grams in weight and is distinguished by its two-tone tail - white below and dark above. The tail is longer than head and body.
The species occurs in rainforest and wet and dry sclerophyll forest. It is particularly common in sub-alpine scree - indeed, the unusually long hindfeet of the species may assist it while leaping from rock to rock in such a habitat. Its broad diet includes grasses, sedges, fruit, subterranean fungi and insects.
Breeding occurs from late spring to late summer, with one or two litters averaging 3-4 young, being produced each year. Gestation is 33 days. Longevity is about 18 months.
New Holland mouse, Pseudomys novaehollandiae
The New Holland Mouse is listed as endangered under the Tasmanian Threatened Species Protection Act 1995
. It only occurs in low numbers - and much of its habitat is unprotected. A listing statement
has been prepared for the New Holland mouse, providing more detailed information including management information.
The smallest (25 grams) of our native rodents, the New Holland mouse is very similar in size and appearance to the introduced house mouse. Although it can be distinguished by its slightly larger ears and heavier build, positive identification is based on the absence of a notch on the upper incisors. The house mouse possesses such a notch.
The New Holland mouse is restricted to the few remaining patches of dry coastal heathland and open, heathy forest on Tasmania's north-east coastline. Its diet consists of seeds, insects, fungi, fruit and leaves.
Breeding occurs from late winter to early spring. Gestation is about 32 days. Litter size is 2-6. One litter is produced in their first year of life, and up to four can be produced in their second (and last) year of life.
Broad-toothed rat, Mastacomys fuscus
The broad-toothed rat is an uncommon resident of buttongrass moorland and alpine heathland, where it feeds on sedges, grasses and seeds. It also occurs on mainland Australia. Fossil evidence shows that the species was once more widely distributed on the mainland.
It is the only mammal species in Tasmania that is restricted to the western part of the State.
Breeding occurs from October to March, with up to two litters of 1-3 young per year. The young are weaned when about five weeks old.
Swamp (velvet-furred) rat, Rattus lutreolus
This common species occurs in a variety of habitats, ranging from wet and dry sclerophyll forests to buttongrass moorlands and coastal heath. It forms extensive systems of runways beneath dense vegetation. Grasses and sedges form the main component of the diet, although insects are occasionally taken.
Breeding begins in spring and runs to autumn. More than one litter, of 3-5 young, may be raised per season. Females from the first litter of the season may give birth themselves during the same breeding season, as sexual maturity is reached at 3 months. Longevity is about 18 months.
Three species of rodent have been introduced to Tasmania - the house mouse (Mus musculus)
, brown rat (Rattus norvegicus)
and black rat (Rattus rattus)
. It is likely that these species entered the state almost as soon as the first European explorers touched ground - perhaps even before!
The brown rat is particularly common in urban areas, whereas the black rat also occurs in rural areas and adjacent bushland. In contrast to our native rodents, the black rat is known for the role it plays in the spread of disease. It was the animal responsible for the plague which ravaged medieval Europe.
The house mouse is widespread through Tasmania, mainland Australia and, indeed, much of the world. It is one of the most successful living mammals.