Brown rat

The brown rat is a very common animal.

It has brown or grey fur. It can live almost anywhere humans live.

These rats are good swimmers. They can also climb tall poles. They like to dig deep holes to live in.

Brown rats eat almost any food. They like eggs and corn. They can even eat small fish.

They have very good hearing. They can also smell things very well. This helps them find food and stay safe.

These rats have many babies very fast. A mother can have many litters each year. This helps their group grow quickly.

The brown rat is a very common animal.

It has brown or grey fur. It can be much bigger than a house mouse.

This rat is an omnivore. That means it eats almost anything. They love scrambled eggs and corn. Some rats even dive for food in rivers.

Brown rats are very smart. They can swim well and climb tall poles. They also dig deep burrows to live in. These rats use sound to talk. They make high noises called ultrasonic vocalizations. Humans cannot hear these sounds without special tools. Some rats even make a chirping sound when they play. This sound is like laughter.

These rats grow their families very fast. A mother can have many litters each year. She can even be pregnant while nursing babies. This helps the group grow very quickly. Most brown rats live for about one year. They usually live in large groups near people.

The brown rat is a very common animal found all over the world.

It is also known by many names, like the street rat or the sewer rat. These rats are quite large compared to other small rodents.

They can weigh much more than a house mouse or a black rat. Most brown rats live near people in big cities. Some are even kept as pets, which are called fancy rats.

Other rats are used in science labs to help researchers learn about biology.

These rats have many special ways to find food and stay safe. They are omnivores, which means they eat almost anything they can find.

They enjoy eating things like scrambled eggs, corn, and carrots. Some rats are very clever and learn to dive for food in rivers. They can also climb slim metal poles to reach bird feeders.

To stay safe, they dig deep burrows to make homes underground. They are also very good at swimming both on top of and under the water.

People have been curious about where these rats came from for a long time.

In the 1700s, some people in England thought they came from Norway. A writer named John Berkenhout helped make this idea popular. He thought they arrived on ships from Norway in 1728. Later, the writer Charles Dickens wrote that people thought they arrived in timber ships. However, scientists eventually realized the rats did not actually come from Norway. Most experts now believe the species started in central Asia or China.

Brown rats have many interesting body facts and numbers. An adult rat can weigh up to 500 grams. Their bodies can be quite long, but their tails are usually a bit shorter. A rat's heart beats very fast, between 300 and 400 times every minute. They also breathe very quickly, about 100 times per minute. While their vision is not very clear, they have a great sense of smell. They can even hear sounds that are too high for humans to hear. These high sounds are called ultrasonic vocalizations.

Watching how rats live can show us how quickly life can grow.

A mother rat can have up to five litters of babies in one year. Each litter can have as many as 14 pups. A mother can even be pregnant while she is still nursing her current babies. This helps a small group of rats grow into a huge population very fast. In just one year, a few rats can turn into 15,000 rats. This is similar to how some plants or insects grow very quickly in nature.

The brown rat, known scientifically as *Rattus norvegicus*, is one of the most successful rodent species on Earth.

It is a large member of the murid family, which includes many types of mice and rats. This species is often called the common rat, street rat, or sewer rat. It has become naturalized in almost every part of the world, except for Antarctica. Because they live so close to people, they are found in nearly every urban environment. They are highly adaptable, allowing them to thrive in cities and various natural habitats.

Physically, the brown rat is built for survival and agility. They typically have brown or dark grey fur with lighter colored underparts. An adult can weigh anywhere from 250 to 500 grams. Their bodies are quite long, though their tails are usually slightly shorter than their head and body combined. The brown rat has several specialized senses to help it navigate. They possess an acute sense of hearing and a highly developed olfactory sense, which is their sense of smell. While their vision is relatively poor, they are dichromats, meaning they perceive colors similarly to a human with red-green colorblindness. Interestingly, they also have UV receptors, which let them see ultraviolet light that humans cannot see.

These rodents are true omnivores, meaning they eat a wide variety of both plant and animal matter.

Their diet is often determined by what is available in their specific environment. In cities, they rely heavily on discarded human food. In other areas, they may hunt for different things. For example, rats near a hatchery in West Virginia catch small fish. Some colonies along the Po River in Italy have even learned to dive for mollusks. This ability to learn new ways to find food is a sign of social learning within the species. They may also eat birds, mice, or small lizards.

One of the most remarkable traits of the brown rat is its ability to reproduce at an incredible speed.

A female can produce up to five litters in a single year. The gestation period, or the time the babies spend developing inside the mother, is only 21 days. A single litter can contain up to 14 pups, though seven is a more common number. Females can even become pregnant again immediately after giving birth. This means a mother can nurse one litter while she is already pregnant with the next. Under ideal conditions, a small group of just two rats could grow to 15,000 in only one year.

Communication in brown rats involves sounds that humans often cannot hear. They use ultrasonic vocalizations, which are high-pitched sounds above the range of human hearing.

Pups use these cries to direct their mothers to help them in the nest. Adult rats also use these sounds to respond to predators or perceived danger. Some rats even produce a high-frequency "chirping" sound during play. This chirping has been compared to laughter and is linked to positive emotions. Rats also make sounds humans can hear, such as "bruxing." Bruxing is a teeth-grinding noise that usually signals happiness or can be used for self-comfort during stress.

There is a long history of confusion regarding the true origins of the brown rat.

In the 18th century, some people in England called them "Hanover rats" to link them to the House of Hanover. The name *Rattus norvegicus* suggests they come from Norway, but this is a misnomer. The naturalist John Berkenhout popularized this name because he believed the rats arrived on Norwegian ships in 1728. However, by the 19th century, scholars realized the rats were not native to Norway. Even the novelist Charles Dickens noted that while people thought they arrived in timber ships from Norway, the rats were actually unknown in Norway at that time. Modern science now shows they likely originated in central Asia or China.

Today, the brown rat plays many different roles in human society. Through selective breeding, humans have created the fancy rat, which is kept as a pet.

We have also developed the laboratory rat, a domesticated subspecies called *Rattus norvegicus domestica*. These rats are essential model organisms used in biological research. Because they are so similar to other mammals, they help scientists understand how biology works. Even in the wild, they show complex traits. Studies in New York City have shown that different rat populations can evolve distinct genomic profiles over time. This means they slowly develop different genetic traits based on the specific neighborhoods where they live.