Norway Rats

Brief:

The Norway rat, Rattus norvegicus, also known as the brown rat, common rat, street rat, sewer rat, wharf rat, or the Norwegian rat is greyish-brown in colour but this varies from pure grey to pure black or any combination of this. They are large and stocky, combined the head and body measure 20-27cm (30-45 cm in length including the tail).

They have a blunt nose, small close-set ears and a long naked tail. They weigh up to 650g. The rat dropping is 19mm long and oblong shaped.

Thought to have originated in northern China, this rodent has now spread to all continents except Antarctica, and is the dominant rat in Europe and much of North America—making it by at least this particular definition the most "successful" mammal on the planet after humans.

Habits

The Norway rat eats meat, fish, flour, seeds, grains, fruits, vegetables and anything a human will eat. They eat 30g of food per day and drink about 15ml water each day. A rat must have water daily to survive.

Norway Rats are capable of mating at three months. Females come into heat every 4 or 5 days and have an average of 3 - 7 litters per year (gestation taking 21-24 days) with 6 - 12 pups per litter. Their eyes open at 6 days, are fully furred by 15 days and will be fully weaned at 3-4 weeks. After giving birth the female goes back into heat in 24 hours. Adults live for approximately one year.

Brown rats have acute hearing, are sensitive to ultrasound, and possess a very highly developed olfactory sense.

Habitat

The Norway Rat generally live communally in outdoor burrows, with a typical burrow having multiple entry and exit points dug under the floors of houses, sheds or other buildings, in banks, in piles of rubble or in rubbish heaps, compost heaps or refuse tips.

During the day rats usually stay in their burrows and come out a night to search for food.

Norway Rats live in small, hierarchical family groups, including one or more dominant male. The dominant males territory extends up to about 100m and is explored daily, any intruders being ejected often after a fierce, sometimes fatal fight. They are neo-phobic (showing a fear of new objects), which makes them cautious, and any new object in their territory takes them several days before they will accept it.

Rats can squeeze through a hole of 13mm diameter. Though not good climbers because of their bulk, the Norway rat can climb up the inside and outside of pipes and jump as much as a metre vertically, drop 15cms without injury and can burrow down to a depth of 1.2m.

Threats

Similar to other rodents, Norway rats may carry a number of pathogens, which can result in disease, including Weil's disease, rat bite fever, cryptosporidiosis, viral hemorrhagic fever, Q fever and Hantavirus pulmonary syndrome.

As well as disease mice can pose a threat to stored goods like food, with an estimated 12-14% of global food production lost to rodent activity.  Damage to buildings is also of major concern, with rodents being documented chewing through concrete and metal shuttering in some extreme cases.  This gnawing behaviour also brings an increased risk of fire as a result of damage to electrical cabling.

Prevention

Poor sanitation and the presence of garbage allow rats to exist in residential areas. Good sanitation will effectively limit the number of rats that can survive in and around the home. This involves good housekeeping, proper storage and handling of food materials and refuse and elimination of rodent harbourage (shelter). Outside dog pens must be properly maintained, to reduce potential rat problems.

On farms where food grains are handled and stored, or where livestock are housed and fed, it is difficult to remove all food that rats can use. In such situations, paying particular attention to removing shelter that rats can use for hiding, resting, and nesting is valuable in reducing rat numbers.

Warehouses, grain mills, and silos are especially vulnerable to rodent infestation. Store bulk foods in rodent-proof buildings, rooms, or containers whenever possible. Stack sacked food on pallets with adequate space left around and under stored articles to allow inspection for signs of rats. Good sanitary practices will not eliminate rats under all conditions, but will make the environment less suitable for them to thrive.

The most successful and permanent form of rat control is to ‘build them out’ by making their access to structures impossible. .

Other options include traps, rodenticides, baiting, and sound/electronic devices.

Others

Photos and information are provided by PelGar.

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