The Norway rat isn't from Norway, and it chirps with delight when tickled
The brown rat's scientific name means Norwegian rat, a mistake popularised by an 18th-century English naturalist. It actually came from northern China. Tickle one and it emits ultrasonic chirps that researchers liken to laughter, too high for human ears, so pet owners use bat detectors to listen in.
John Berkenhout, writing in 1769, named the species Mus norvegicus, believing it had arrived in England on Norwegian ships in 1728. Others called it the Hanover rat to mock the new royal house. Victorian scholars guessed at origins in Ireland, Gibraltar or even the Norman invasion. Charles Dickens's journal pointed out that the rat was common in Britain while still unknown in Norway, and by the 20th century naturalists had settled on Central Asia, most likely China.
Rattus norvegicus now lives on every continent except Antarctica, almost always near people, and dominates in Europe and much of North America. Adults typically weigh 140 to 500 grams; tales of cat-sized rats are exaggerations or cases of mistaken identity. They swim well above and below water, dig extensive burrows, and have been seen climbing thin metal poles to raid bird feeders. Hearing and smell are acute, but eyesight is poor. Rats see colours much like a human with red-green colour blindness, yet can detect ultraviolet light.
Their sound world is rich. Pups use ultrasonic cries to steer their mothers, and by two weeks old they fall quiet around adult males as a defence. Tickling, play and anticipated rewards trigger the laugh-like chirps, and tickled rats bond with the person doing it and come back for more, though the habit fades with age. Audible sounds include bruxing, a contented teeth-grinding sometimes accompanied by boggling, when the eyes rapidly bulge in and out.
They will eat nearly anything; in taste tests, favourites included scrambled eggs and cooked corn, while raw celery and beets ranked last. Local cultures emerge: rats by the Po River in Italy dive for molluscs, a learned behaviour, and those on the North Sea island of Norderoog hunt sparrows and ducks. In New York City, neighbourhood populations have even developed distinct genomes. Selective breeding also produced the pet fancy rat and the laboratory rat.
Source: Brown rat
