Observations by mironboski

Scientific and Common Names:

Rattus norvegicus is the scientific name of the rodent species. In order of prevalence, common names include; brown rat, common rat, street rat, sewer rat, Norway rat, Norwegian rat, Hanover rat, and wharf rat.
The binomial name Rattus norvegicus denotes an erroneous nomenclature as the species of rat did not originate from Norway. Berkenhout, an English naturalist was first to label the brown rat with its current scientific name. He believed that the rat had entered England via ships arriving from Norway. However, it has been determined that this species of rat wasn’t even present in Norway in the year 1728 when Berkenhout inaccurately gave the brown rat its infamous name. Greater analysis into the origins of the brown rat put its modern roots to central Asia, more specifically China. Even with this in mind the brown rat is commonly mislabeled as the Norway rat.

Habitat and Geographic Range:

Rattus norvegicus has an incredible geographic range as it lives on all continents except for Antarctica. The brown rat dominates urban areas and in a sense was spread by human exploration. Their habitats are often dependent upon their environment, but a common feature includes a shelter that’s conducive to their borrowing behaviour, allowing for moderate warmth for nesting, and protection from the external environment and predators. For this reason places like sewers, attics, and alleyways are highly selected favored. Brown rats will typically stay within 20m (66ft) of their nest if adequate food is available. In a more natural environment, without interference of humans, brown rats have a greater prevalence in damp areas, like marshes and river banks.

Size/Weight and Lifespan:

The brown rat is a large rodent, in fact it is one of the biggest murids. Measuring on average between 20-25 cm (8-10 in), with an additional length of 18-24 cm (7-10 in) for its tail. The female marks the lower end of the spectrum, whilst the male has a potential to reach the larger outlined size. In regards to weight, the fully matured adult body has an average mass of 350 g (12 oz) in males, and close to 250 g (9 oz) in females. Outliers have been recorded with a mass of 900-1000g (32-35 oz), but these are uncommon occurrences. The typical lifespan is two years, with a maximum of three years. However, the majority do not exceed one year due to a very high mortality rate of about 95% due to predators, and interspecies conflict.

Diet:

Part of the brown rats success in spreading too many environments relies on its open diet adaptability. Being an omnivore, it consumes a wide variety of foods. The most common forms of sustenance include cereal foods, as these are produced or found in most urban locations. The environment often dictates the food availability, and as a result heavily influencing their diet. Brown rats living close to a shoreline will consume fish-based diets, while mainland rats will eat foods typically produced by humans.

Reproduction and Communication:

The brown rat is able to reproduce throughout the year, on average a female will have five litters per year. The typical litter size is seven, but can reach up to fourteen. With a sexual maturation time of five weeks, and a gestation period of three weeks, a rat population can grew very quickly under suitable conditions. It’s not uncommon for a rate population to grow by a factor of ten in fifteen weeks.
Brown rats communicate amongst specie’s members via ultrasonic vocalizations. These start at an early age and at this point signify maternal search behaviour. As rats become older, the random vocalization decrease in response to interspecies threats. During mating and mate signalling both sexes will emit the ultrasonic communications. Brown rats can allows produce audible sounds able to be heard by humans. These are often noted during high-stress scenarios when the rat is threatened. This form of communication is described as ‘squeaking’ or ‘clicking’.

Predation:

The brown rat’s most revered predator are humans. Since the majority of rats are centered in urban areas, they must battle for territory with humans. Rats are perceived as invasive, unwanted rodents that are capable of spreading disease. For these reasons humans will spend money to exterminate them from their homes and businesses. Common forms of rat removal include baits, traps and professionally managed techniques. Domestic cats and dogs are also predators to unwanted rats. In the wild, rats face a wider range of predators including; birds of prey, like hawks, owls or falcons, some snakes, and larger felines.

Conservation Status:

There are absolutely no conservation efforts for the brown rat. On the contrary, there are heavily funded attempts to remove rats from urban settings. Places like New York and Paris have invested millions of dollars to control the rat population. The only silver lining is for albino laboratory rats. This fraction of the brown rat population is used for biological, medical and psychological testing. For these reason specific genetic breeding is conducted in order to perform more accurate experiments. Rats are used due to their ability to reach sexual maturation early, as well as being easy to handle and breed in captivity.

Did You Know?

Alberta, Canada, is the largest metropolitan city in the world with the lowest brown rat population. In the 1950’s the provincial government took steps to eliminate the growing problem. The province initially used arsenic to exterminate the rats, but after one year of use they resorted to a safer option of warfarin. To prevent future growth, the province implemented a legislative measure whereby only zoos, universities and research centers are allowed to keep rats. Pet rats are outlawed and punishable for up to $5,000 and a 60-day jail sentence. Also, the brown rat is the only species of rat capable of surviving the harsh winters in Alberta.

Out of all the mammals to have ever existed, the rat is most notorious killer of humans. Throughout human history there have been numerous diseases that have been spread by the rat. The Bubonic plague that was caused by a bacterium Yersinia pestis, was aided in transmission throughout Europe by rats. Other forms of deathly disease like trichinosis, and toxoplasmosis have been spread by rats as well. The estimated death account attributed to rats, direct and indirect, ranges from 150-500 million.

Work cited:

Brudzynski, Stefan M. (2005). "Principles of Rat Communication: Quantitative Parameters of Ultrasonic Calls in Rats". Behavior Genetics. 35 (1): 85–92. doi:10.1007/s10519-004-0858-3.

Clark, B. R.; Price, E. O. (1981). "Sexual maturation and fecundity of wild and domestic Norway rats (Rattus norvegicus)". Journal of Reproduction and Fertility. 63 (1): 215–220. doi:10.1530/jrf.0.0630215.

Ruedas, L. (2008). "Rattus norvegicus". IUCN Red List of Threatened Species. Version 2011.1. International Union for Conservation of Nature.

White, N; Adox, R; Reddy, A; Barfield, R (1992). "Regulation of rat maternal behavior by broadband pup vocalizations". Behavioral and Neural Biology. 58 (2): 131–137. doi:10.1016/0163-1047(92)90363-9.