The brown rat was never actually from Norway, yet for centuries, the world has called it the Norway rat. This misnomer was popularized in 1769 by English naturalist John Berkenhout, who believed the species had migrated to England on ships from Norway in 1728. The reality is far more complex and geographically distant. The species likely originated in northern China and neighboring areas, spreading to Europe and the rest of the world only during the Middle Ages. By the 18th century, the name Hanover rat was used in England to link the pest problem to the House of Hanover, but the scientific name Rattus norvegicus stuck despite the geographical error. Charles Dickens himself noted the absurdity of the name in his journal All the Year Round, pointing out that the rat was unknown in Norway even when it was common in England. Instead, the species traveled from Persia to England and then to other countries visited by English ships, eventually displacing the black rat in many parts of the world. The brown rat's global dominance is a testament to its adaptability, as it has now spread to all continents except Antarctica, living wherever humans live, particularly in urban areas.
A Master of Urban Survival
The brown rat is a true survivor, thriving in the most hostile environments created by humans. It is a nocturnal, omnivorous rodent that can weigh up to 1.5 kilograms, making it one of the largest muroids. Its physical adaptations are remarkable: it has acute hearing, sensitive to ultrasound, and possesses a highly developed olfactory sense. Its vision is poor, with pigmented rats having 20/600 vision and non-pigmented rats having 20/1200 vision, yet they can see ultraviolet light that humans cannot. The brown rat is a good swimmer, both on the surface and underwater, and has been observed climbing slim round metal poles several feet in order to reach garden bird feeders. It digs well, often excavating extensive burrow systems that provide shelter, food storage, and safe, thermo-regulated nest sites. In the absence of humans, brown rats prefer damp environments, such as river banks, but the great majority are now linked to man-made environments, such as sewage systems. In cities, they tend not to wander extensively, often staying within 100 meters of their nest if a suitable concentrated food supply is available, but they will range more widely where food availability is lower. The brown rat's ability to adapt to human environments has made it a dominant species, with some estimates suggesting there are as many rats in cities as people.The Secret Language of Rats
Brown rats communicate in ways that are far more sophisticated than simple squeaks. They are capable of producing ultrasonic vocalizations, which are too high in pitch for humans to hear without special equipment. As pups, young rats use different types of ultrasonic cries to elicit and direct maternal search behavior, as well as to regulate their mother's movements in the nest. Adult rats will emit ultrasonic vocalizations in response to predators or perceived danger, and the frequency and duration of such cries depend on the sex and reproductive status of the rat. The female rat also emits ultrasonic vocalizations during mating. In addition to ultrasonic calls, brown rats produce communicative noises capable of being heard by humans. The most commonly heard in domestic rats is bruxing, or teeth-grinding, which is most usually triggered by happiness, but can also be 'self-comforting' in stressful situations, such as a visit to the vet. The noise is best described as either a quick clicking or 'burring' sound, varying from animal to animal. Vigorous bruxing can be accompanied by boggling, where the eyes of the rat rapidly bulge and retract due to movement of the lower jaw muscles behind the eye socket. Brown rats also produce short, high frequency, ultrasonic, socially induced vocalization during rough and tumble play, before receiving morphine, or mating, and when tickled. The vocalization, described as a distinct 'chirping', has been likened to laughter, and is interpreted as an expectation of something rewarding. In research studies, the chirping is associated with positive emotional feelings, and social bonding occurs with the tickler, resulting in the rats becoming conditioned to seek the tickling.