Cornwall Mammal Group
Common Rat-(Rattus norvegicus)
Order: Rodentia, Cornish Name: Rath
Recognition:
Despite its recent arrival, the common or
brown rat is one of our most numerous
mammals. It is often found in domestic and
industrial buildings as well as agricultural
areas. The common rat has a shabby grey or
brown coat, and a pointed nose with
prominent ears and eyes. There is a long
scaly tail which may be almost as long as the body. The body of a large male rat can be 280 mm long and weigh 500 g, although the average is closer to 350 g (250 g for females). Common rats are often found near water and are excellent swimmers. They may be confused with water voles, so look for the long tail, pointed face, and obvious ears of the rat compared to the rounder head and
shorter tail of the water vole. The very rare black rat, which may also be brown, has larger, hairless ears and a longer, thinner tail.
The Isles of Scilly Seabird Recovery Project is currently (2013) working on a programme to eradicate common rats from the islands of St Agnes and Gugh so as to protect shearwaters, petrels and puffins from the depredations of the rats.
Conservation:
Globally a significant pest species
damaging stored food crops and property and a vector of several important human diseases, particularly leptospirosis (Weil’s disease). The common rat may have major impacts on populations of ground nesting birds, especially in island habitats. It is extensively controlled through poisoning, trapping and shooting. Secondary poisoning of its predators, especially mustelids, may impact these species.
© Chris Robbins
Did you know?:
Common rats are also known as the brown, sewer or Norway rat (from where it was originally thought to have arrived, hence the scientific name norvegicus,
although it probably came via Denmark), common rats arrived in the UK in the
eighteenth century and rapidly displaced black, or ship, rats from much of the
country. The black rat (Rattus rattus) is now confined to a few port areas.
Droppings are
up to 20 mm
long and taper
to a point and
are often
deposited in
latrines.
Burrowsare
often found in banks and hedgerows; the entrance is about 40 mm cross with a narrow beaten trail leading to it.
Forepaw prints show 4 toes and are up to 18mm long, rear paws up to 35 mm long with 5 toes. There are rarely any tail drag marks.
Common rats occur in most environments but are particularly associated with farm
buildings, rubbish dumps, sewers,
warehouses and urban waterways. They inhabit extensive burrow systems and may take advantage of voids in buildings or old rabbit burrows. At low densities communal burrows are occupied by single males with a
harem of up to 6 related females. As densities increase a single male becomes
dominant over large communities but females mate with any available males.
Common rats are omnivorous - eating grain, fruit, eggs, other animals and human
foodstuffs, and they may travel up to 3 km in search of food. Older rats often allow
younger animals to test environments and food, making the senior animals difficult
to trap or poison.
Common rats breed throughout the year, producing up to 5 litters of 6 to 11 pups each
year. The blind naked pups that grow rapidly and are weaned at 3 weeks and are capable of breeding at 3 months. A single pair could potentially produce 2000 progeny in a year but 99% of all pups die in the first year. There are estimated to be about 6.5million rats in the UK.
Young rats are predated by foxes, stoats and other members of the weasel family as well as cats and birds of prey, but larger rats are rarely taken and most die as a result of road traffic, or pest control. In the UK control is primarily through the use of anti-coagulants since rats quickly learn to avoid fast-acting poisons. The use of poisons is restricted by increasing evidence of physiological, and to some extent behavioural, resistance, as well as the issues of impacts on predators. Good hygiene and rodent-proofing of buildings are the most effective ways of controlling infestations.
Survey Methods:
Pest control reports, road casualties and cat or dog kills provide most records.
Frequently around human habitation so incidental sightings common, especially
associated with domestic animal feed and bird feeders.
Records:
2007-2012: 301
2002-2007: 831
Pre-2001: 287
Total: 1419
Distribution:
The common rat is
found throughout
Cornwall and the
Isles of Scilly,
although records
have declined in recent years. Probably originating in the central Asian steppes,
the common rat is virtually ubiquitous, occurring worldwide, especially associated with human habitation, agriculture, and industry.
