History of the Domesticated Rattus Norvegicus

The Norway rat is actually not from Norway. Also known as the brown rat, it has made its way west from Asia and proved to be a highly adaptive and commensal species. Incredibly little is known about the native area and activities of the brown rat before they became a commensal species. The brown rat quickly began to migrate alongside humans making its way to most continents.

The earliest known domestication event occurred between 1600 and 1700 in Japan. (Although we have art from China depicting unusually colored rats from as early as the 1500s) In the 1800's in Europe, they were domesticated and used for blood sport. In the early 1900's laboratory use began in the states. In 1901 Mary Douglas won the first show ribbon with an early hooded variety. By the late 70's we saw the formation of The National Fancy Rat Society and The American Fancy rat and Mouse Association.

Ethology and Its Use

Ethology is the study of animal behavior (even the human animal) especially in its natural state. Ethology informs ethics in all areas of animal keeping. Zoos, laboratory scientists, wildlife rehab, hobby breeding, or large-scale farming operations use ethology when considering the ethics of their husbandry and behavior of their animals.

Ethology seeks to understand the natural behaviors of animals in their native habitat. Unfortunately, we have very little research on the rat before human interventions. Yet what we know of their natural behaviors can still help us replicate their natural environment and provide for an outlet of biologically appropriate behaviors which dramatically decreases the likelihood of stress behaviors and illness in our captive population.

What does ethology of the rat tell us about their natural behaviors and what we should provide?

Rats are fossorial, they construct underground tunnels, and burrowing is an instinctual behavior. Providing this usually means modifying enclosures to hold 6" to 12" of wood or coconut coir substrate.
Rats thrive on environmental variety. Because they adapt to change so easily having the same enclosure set up can be downright boring and result in stress behaviors. It's also imperative that rats have access to safe spaces outside of their enclosure.
Rats are diurnal omnivores that like to forage and hunt. Hiding a variety of species appropriate food into the enclosure provides rats a foraging experience. While using cat wands (such as feathers) and pea fishing (a bowl of water with peas inside) can be an excellent outlet for hunting behaviors. You can add small, dried fish and bugs to their daily snacks as well.
Rats chew! They are notorious for the damage they can do with their teeth. A rat's teeth continually grow, and they must chew to keep them filed down. We can encourage appropriate chewing by having a variety of safe chewing media available in enclosures. Things like apple wood, pumice stones, cholla wood, cardboard, and even bones are good options. Also, because rats have poor eyesight, exploring the world with teeth is a natural behavior. Don't be alarmed if they nibble fingers lightly at first.
Rats have poor eyesight but excellent smell, hearing, touch and taste. In the wild, novel smells, sounds and sensations would inform the rat about its environment. Letting our rats experience various surfaces, smells and tastes through new foods, beddings, areas for exploration and human interactions can engage these senses.

Stress Behavior in rats

When captive animals' biological needs aren't met or they are experiencing pain, they can display a host of stress behaviors. Common stress signals in rats can include:

Sudden Neophobia in an otherwise well-tempered and socialized rat
Bar chewing
Hunched posture (could also indicate illness)
Barbarism
Decreased positive social interactions (allogrooming, playing)
Decreased activity levels
Increased infighting within established colonies
Increased susceptibility to URIs
In cage aggression towards humans or other fear behaviors
Aggression towards, or rejection to, novel rats