The Norway rat or brown rat (Rattus norvegicus) is one of the most familiar common rats. It is thought to occupy almost every continent except for Antarctica. Brown rats are most likely to live near human populations precisely because they get easy access to food. They have got many names such as street rat, sewer rat, wharf rat, or Hanover rat. It is the brown rat that people often talk about. They are seen nearly everywhere in urban areas.
Norway Rat Facts
Anatomy
- Norway rats have dark brown to grey fur and they are larger than the black rat or a house mouse.
- Adult brown rats average 20 to 25 cm (8 to 10 in) in body length and a tail further adds 18 to 25 cm (7 to 10 in).
- Males are larger than the females. The average weight of males is 350 g (12 oz) while females weigh up to 250 g (9 oz). The brown rat can be as heavy as 900 to 1,000 g (32 to 35 oz).
- They have got remarkable hearing sense because they possess extremely advanced olfactory sense.
- Brown rats have 300 – 400 heart beats per minute.
- They have poor sight and as such they don’t rely on vision.
Geographic Range
- Norway rats are one of the most widespread mammals. They occur in Asia including northern China to the United Kingdom, United States, Alberta (Canada), Alaska, to as far as New Zealand.
Behavior
- The Norway rat is a nocturnal animal. It is an excellent swimmer is able to swim underwater.
- They have got the amazing ability to climb the poles to reach the backyard feeders. The poles might be many feet high.
- Brown rats are regular diggers and they build good wide burrow systems.
- They are known to produce ultrasonic vocalizations in order to drive off the predators. Females however emit ultrasonic only during mating.
- Norway rats will produce short vocals of high frequency either during play or during mating. These calls are meant to make their counterparts involve socially. The sounds they produce seem more like chirping. The frequency of the sounds gets low when the rat is going down to sleep.
- Prominent among their communicative noising is teeth-grinding or bruxing which they make when the rats are happy.
- They are typically found in large hierarchical groups and or cellars. The one at the lower end of hierarchy dies first when the food goes short.
- Norway rats play, jump, and tumble in groups.
- In captivity and in the wild Norway rats make burrows to store food and to seek cover from predators.
Feeding Ecology & Diet
- Since brown rats live in urban areas, they have a varied diet. In fact rats eat nearly everything from cereals to the scrambled eggs.
- Norway rat’s diet also consists of raw beets, raw celery, cooked corn kernels, and peaches.
- Some of the rats that live near the banks of Po River are thought to dive for mollusks.
Reproductive Biology & Lifecycle
- Under favorable conditions, Norway rats breed all year round.
- A female produces 5 litters each year. The maximum litter size is 14 but 7 is common.
- The gestation period lasts about 3 weeks.
- Norway rats attain maturity at 35 days age.
- The average lifespan of brown rats is 1 year but they may live up to 3 years.
Conservation Status
Least Concern
