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Brown rats have acute hearing, are sensitive to ultrasound, and possess a very highly developed olfactory sense.
Their average heart rate is 300 to 400 beats per minute, with a respiratory rate of around 100 per minute.
Stories of rats attaining sizes as big as cats are exaggerations, or misidentifications of other rodents, such as the coypu and muskrat.
In fact it is common for breeding wild brown rats to weigh (sometimes considerably) less than 300 g (11 oz).
By the early to middle part of the 19th century, British academics believed that the brown rat was not native to Norway, hypothesizing (incorrectly) that it may have come from Ireland, Gibraltar or across the English Channel with William the Conqueror.
"Now there is a mystery about the native country of the best known species of rat, the common brown rat.
One of the largest muroids, it is a brown or grey rodent with a body up to 25 cm (10 in) long, and a similar tail length; the male weighs on average 350 g (12 oz) and the female 250 g (9 oz).
The brown rat is a rather large true murid and can weigh twice as much as a black rat and many times more than a house mouse.
The length is commonly in the range of 20 to 25 cm (8 to 10 in), with the tail a further 18 to 25 cm (7 to 10 in), thus being roughly the same length as the body.
Selective breeding of Rattus norvegicus has produced the laboratory rat, a model organism in biological research, as well as pet rats. However, the English naturalist John Berkenhout, author of the 1769 book Outlines of the Natural History of Great Britain, is most likely responsible for popularizing the misnomer.
Berkenhout gave the brown rat the binomial name Rattus norvegicus, believing it had migrated to England from Norwegian ships in 1728.