There is little doubt that the South Australia has some fascinating and inspiring countryside from the rugged coastline of the south east to the wild expanses of outback in the north. However, it is often what is right under our noses that can prove most interesting. With that in mind I decided to try out my new Tamron 18-400 lens in the back yard.
The brown rat (Rattus norvegicus), also known as the common rat, street rat, sewer rat, Hanover rat, Norway rat, Norwegian rat, Parisian rat, water rat, or wharf rat, is one of the best known and most common rats. Thought to have originated in northern China, this rodent has now spread to all continents except Antarctica, and is the dominant rat in Europe and much of North America, making it, by at least this particular definition, the most successful mammal on the planet alongside humans. With rare exceptions, the brown rat lives wherever humans live, particularly in urban areas. Selective breeding of the brown rat has produced the fancy rat as a pet, as well as the laboratory rat – rats used as model organisms in biological research.
Possibly originating from the plains of Asia, northern China and Mongolia, the brown rat spread to other parts of the world sometime in the Middle Ages. The question of when brown rats became commensal with humans remains unsettled, but as a species, they have spread and established themselves along routes of human migration and now live almost everywhere humans are. Originally called the "Hanover rat" by people wishing to link problems in 18th century England with the House of Hanover, it is not known for certain why the brown rat is named Rattus norvegicus (Norwegian rat), as it did not originate from Norway. However, the English naturalist John Berkenhout 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. 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. Though the assumptions surrounding this species' origins were not yet the same as modern ones, by the 20th century, it was believed among naturalists that the brown rat did not originate in Norway, rather the species came from central Asia and (likely) China.
The fur is coarse and usually brown or dark grey, while the underparts are lighter grey or brown. The head and body length ranges from 5.9 to 11.0 inches while the tail ranges in length from 4.1 to 9.4 inches, therefore being shorter than the head and body. Adult weight ranges from 140 to 500 g (4.9 to 17.6 oz). Exceptionally large individuals can reportedly reach 900 to 1,000 g (32 to 35 oz) but are not expected outside of domestic specimens. Stories of rats attaining sizes as big as cats are exaggerations, or misidentifications of larger rodents, such as the coypu and muskrat.
Brown rats have acute hearing, are sensitive to ultrasound, and possess a very highly developed olfactory sense. The vision of a pigmented rat is poor, around 20/600, while a non-pigmented (albino) with no melanin in its eyes has both around 20/1200 vision and a terrible scattering of light within its vision. Brown rats are dichromates which perceive colors rather like a human with red-green colorblindness, and their colour saturation may be quite faint. Their blue perception, however, also has UV receptors, allowing them to see ultraviolet lights that some species cannot.
The brown rat is nocturnal and 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. Brown rats dig well, and often excavate extensive burrow systems.
Brown rats are capable of producing ultrasonic vocalizations. 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. Although pups will produce ultrasounds around any other rats at 7 days old, by 14 days old they significantly reduce ultrasound production around male rats as a defensive response. Adult rats will emit ultrasonic vocalizations in response to predators or perceived danger.
Rats may also emit 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. Like most rat vocalizations, the chirping is too high in pitch for humans to hear without special equipment. 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. However, as the rats age, the tendency to chirp appears to decline.
Brown rats also 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. In addition, they commonly squeak along a range of tones from high, abrupt pain squeaks to soft, persistent 'singing' sounds during confrontations.
The brown rat is a true omnivore and will consume almost anything, but cereals form a substantial part of its diet. Martin Schein studied the diet of brown rats and came to the conclusion that the most-liked foods of brown rats include scrambled eggs, macaroni and cheese, raw carrots, and cooked corn kernels. According to Schein, the least-liked foods were raw beets, peaches, and raw celery.
Foraging behavior is often population-specific, and varies by environment and food source. Brown rats living near a hatchery in West Virginia catch fingerling fish. Some colonies along the banks of the Po River in Italy will dive for mollusks, a practice demonstrating social learning among members of this species. Rats on the island of Norderoog in the North Sea stalk and kill sparrows and ducks.
The brown rat can breed throughout the year if conditions are suitable, with a female producing up to five litters a year. The gestation period is only 21 days, and litters can number up to 14, although seven is common. They reach sexual maturity in about five weeks. As a result, the population can grow from 2 to 15,000 in a year.
The maximum life span is three years, although most barely manage one. A yearly mortality rate of 95% is estimated, with predators and interspecies conflict as major causes. Brown rats live in large, hierarchical groups, either in burrows or subsurface places, such as sewers and cellars. When food is in short supply, the rats lower in social order are the first to die. If a large fraction of a rat population is exterminated, the remaining rats will increase their reproductive rate, and quickly restore the old population level.
Rats commonly groom each other and sleep together. Rats are said to establish an order of hierarchy, so one rat will be dominant over another one. Groups of rats tend to "play fight", which can involve any combination of jumping, chasing, tumbling, and "boxing". Play fighting involves rats going for each other's necks, while serious fighting involves strikes at the others' back ends. If living space becomes limited, rats may turn to aggressive behavior, which may result in the death of some animals, reducing the burden over the living space. Rats will fluff up their hair, hiss, squeal, and move their tails around when defending their territory.
Selective breeding of albino brown rats rescued from being killed in a now-outlawed sport called rat baiting has produced the albino laboratory rat. Like mice, these rats are frequently subjects of medical, psychological and other biological experiments, and constitute an important model organism. The brown rat is kept as a pet in many parts of the world. Australia, the United Kingdom, and the United States are just a few of the countries that have formed fancy rat associations, establishing standards, orchestrating events, and promoting responsible pet ownership.The many different types of domesticated brown rats include variations in coat patterns, as well as the style of the coat, such as Hairless or Rex, and more recently developed variations in body size and structure, including dwarf and tailless fancy rats.
A working rat is any rat which is trained for specific tasks as a working animal. Rats have been trained to appear in magic acts, music videos, movies, and television shows. Samantha Martin, a professional animal trainer, has claimed that rats are one of the easiest animals to train due to their adaptability, intelligence, and focus. By being trained to carry a string through holes in walls, a rat can help economically wire a building for the Internet; afterwards, people use the string to pull the computer link cable through. In the Netherlands, police have begun using brown rats to sniff out gunshot residue. Ed Kraszewski, spokesman for the task force, has said that the rats are easier and cheaper to train than dogs. Domestic rats have been trained as service animals, such as to identify damaging muscle spasms for people whose ability to sense this has been compromised by their disability.
