Rodents

There are three main pest species of rodent found throughout Australia:

  • Brown rat,
  • Roof rat and
  • House mouse

BROWN RAT

The Brown Rat (Rattus norvegicus) is one of the most common rats and also one of the largest. Thought to have originated in northern China, this rodent has now spread to all continents. It lives wherever humans live, particularly in urban areas. Other names for the species include Norwegian Rat, Wharf Rat, Sewer Rat and Common Rat.

Food & habitat

The Brown Rat is a true omnivore and will consume almost anything, with cereals forming a substantial part of the diet. Martin Schein, founder of the Animal Behaviour Society in 1964, studied the diet of Brown Rats and came to the conclusion in his paper "A Preliminary Analysis of Garbage as Food for the Norway Rat" that the most-liked food of Brown Rats was (in order) scrambled eggs, macaroni and cheese, and cooked corn kernels. Their least-liked food was raw beets, peaches, and raw celery.

Brown Rats live where humans live. Humans provide an abundant food source and warmth inside houses during the colder periods of the year. They are usually active at night and are good swimmers, both on the surface and underwater, but are poor climbers. They dig well, and often excavate extensive burrow systems.

Appearance

The fur is coarse and usually brown or dark grey and the underparts are lighter grey or brown. The length can be up to 40 cm, with the tail a further 25 cm. Brown Rats have acute hearing and are sensitive to ultrasound. Their vision is poor and they are unable to detect colour and are blind to long-wave light.

Breeding

The Brown Rat can breed throughout the year if conditions are suitable, producing up to five litters a year. The gestation period is only 21-23 days and litters can number up to fourteen, although seven is common. The maximum life span is up to three years. Brown Rats live in large hierarchical groups, either in burrows or subsurface places such as sewers and cellars. When food is in short supply, the rats lower in social order are the first to die. If a large fraction of a rat population is exterminated, the remaining rats will increase their reproductive rate, and quickly restore the old population level.

Diseases

Brown Rats are known to carry disease, including Weil's disease, cryptosporidiosis, Viral Haemorrhagic Fever (VHF), Q fever and Hantavirus pulmonary syndrome. Brown Rats rarely, if ever, carry bubonic plague.

ROOF RAT

The Roof Rat (Rattus rattus), also known as the Black Rat, Ship Rat or House Rat) is a common long-tailed rodent. The species originated in tropical Asia and spread through the Near East in Roman times before reaching Europe in the 8th Century and spreading with Europeans across the world.

Food & Habitat

Today it is again largely confined to warmer areas, having been supplanted by the Brown Rat (Rattus norvegicus) in cooler regions. Compared to the Brown Rat, it is a poorer swimmer, but more agile and a better climber, tending even to flee upwards. It is nocturnal and omnivorous, with a preference for grains.

Appearance

Despite of its common names [Black rat], the Roof Rat comes in several colours but in general is usually black to light brown in colour with a lighter underside. A typical rat will be 15 to 20cm long with a further 20 cm of tail.

Breeding

In a suitable environment it will breed throughout the year, with a female producing three to six litters of up to ten young. Females may regulate their production of offspring during times when food is scarce, producing as few as only one litter a year. The Roof Rat lives for about 2-3 years. Social groups of up to sixty can be formed.

Diseases

The Roof Rat has been known to carry a number of diseases, of which bubonic plague, typhus, toxoplasmosis and trichinosis are the most well-known.

HOUSE MOUSE

The House Mouse (Mus musculus) or common house mouse is believed to be the second most populous mammalian species on Earth, second only to Humans.

Food & Habitat

House mice almost always live in close proximity to humans. Getting mice in one's house is very common. They particularly like to come inside during the cold winter months. Mice are mostly active during dusk or night, are good jumpers, climbers and swimmers but prefer to be away from bright lights. They live in a wide variety of hidden places that are near food sources and construct nests from various soft materials.

House mice primarily feed on plant matter, but they will also eat meat and dairy products. They will drink water but require little of it, relying mainly on the moisture present in their food. They will eat their faeces to acquire nutrients produced by bacteria in their guts. Mice are afraid of rats, which often kill and eat them.

Appearance

House mice are light brown to black, with short hair and a light belly. The ears and tail have little hair. Adults body length (including tail) is about 15-19 centimetres long, with the tail usually accounting for most of the length.

Breeding

Mice are territorial and one dominant male usually lives together with several females and young. Females reach sexual maturity at about 6 weeks and males at about 8 weeks, but both can breed as early as 35 days. Breeding occurs throughout the year and the gestation period is about 19-21 days. One female can have some 5-10 litters per year containing 3-14 young (generally 6-8), so their population can increase very quickly. In protected environments, the House Mouse can often live two to three years.

Diseases

House mice can transmit diseases, and their droppings can spoil foods. They can also cause substantial damage when feeding on grain.

References

Museum Victoria - Introduced Rodents

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