What is my rat doing? FAQ

1.0 Sounds rats make

1.1 Why is my rat making a grinding sound with its teeth?

Rats grind their front teeth together producing a grinding sound called bruxing or chattering. Rats probably grind their teeth together to wear them down (a process called thegosis). A rat's incisors grow continuously. This constant growth enables rats to spend their lives gnawing on things without wearing their teeth down to the gum. But it also means that rats must use their teeth continually to keep them from growing too long, hence the tooth grinding.

Rats grind their teeth in times of stress. For example, a pet rat may grind its teeth at the vet's office, or during a tense interaction with another rat, or when the rat experiences pain. Anecdotally, rats may also grind their teeth when they are relaxed, rather like purring in a cat.

To hear a sound clip of a rat bruxing and chattering, visit the Norway rat vocalizations page.

Here's more on rat teeth.

Rats make a whole variety of vocalizations, including peeps, chirps, squeaks, and shrieks. As a general rule, audible vocalizations are signs of protest or stress.

For example, a rat may peep a little while being petted by you or groomed by another rat, indicating mild protest. Long squeaks produced during a tense interaction with another rat probably indicating distress. A shriek or scream during a fight, or if its tail is pinched, probably indicate strong distress or pain.

Rats do emit sounds that are associated with pleasure, but these sounds are very high pitched and above our range of hearing.

To hear some of the different vocalizations rats make, visit the Norway rat vocalizations page.

Visit the vocal communication section of the Norway rat behavior repertoire.

More on rat hearing.

Occasionally, rats may hiss. Hissing is usually a sign of distress and is given at times of stress. For example, a rat may hiss during a tense social interaction with another rat.

2.0 Bizarre movements rats do

2.1 Why do my rat's eyes bulge in and out?

Sometimes, a rat's eyes may vibrate rapidly in and out of the eye socket, a phenomenon called eye boggling. This odd eyeball movement often occurs at the same time as bruxing, or tooth grinding. The reason bruxing and eye boggling occur together is anatomical: a part of the muscle that pulls up the rat's lower jaw passes through the eye socket, behind the eyeball. When a rat grinds its teeth, it moves its lower jaw rapidly up and down, and the contractions of the jaw muscle vibrate the eyeball in and out of the socket in time with the jaw.

Eye boggling is associated with intense bruxing. Anecdotally, eye boggling occurs at times of great contentment and relaxation.

The rat uses his whiskers to gain information about its surroundings through touch. Using tiny muscles around each whisker, the rat sweeps its whiskers back and forth, brushing them over everything within a few inches of its face, and gleans an image of the world around it. Sometimes whiskers touch the same object several times in a different place, providing a three dimensional picture of the object.

Whiskers are extremely sensitive, more sensitive than a human's fingertips. Rats use their whiskers to navigate, balance, find and discriminate food, and in social interactions with other rats. At short distances rats use their whiskers more than their eyes to determine depth.

More on the world through a rat's whiskers

2.3 Why does my female rat freeze and arch her back?

Female rats freeze, arch their backs downward, push their rumps upwards, and move their tails to one side when they are in heat (every 4 days or so). This position is the female mating posture, called lordosis. Lordosis makes copulation possible. Lordosis is a reflex that is triggered by a touch on the flanks when the female is in heat. This touch is supposed to come from a male rat as he mounts the female, but a human can trigger lordosis too by touching the female on the lower back when she is in heat.

Here's more on rat reproductive behavior.

2.4 Why does my female rat vibrate her ears really fast?

Sometimes, a female rat may vibrate her ears rapidly back and forth, sometimes called ear wiggling. This vibration may be so rapid that her ears become a blur. As with lordosis, ear vibration is a sign that the female rat is in heat. The function of ear vibration is unknown, but it may be a signal of sexual availability that male rats find very attractive.

Here's more on rat reproductive behavior.

2.5 Why does my rat wag its tail?

Rats may "wag" or writhe their tails on the ground. This action has many names, such as tail wagging, tail swishing, and tail writhing. Tail wagging may involve the whole tail or as little as the tail tip.

The function of tail wagging is unknown in rats, but it appears to be associated with excitement and tension. For example, rats may writhe their tails during aggressive encounters with each other, or when facing a predator.

Some rats, especially pink eyed albinos, often sway from side to side. Albino rats have extremely poor vision, and this swaying may help them see better. Dark-eyed rats may sway or bob their heads up and down too, though they tend to do so less frequently than albino rats. Head bobbing in dark-eyed rats is usually seen before the rat takes a big jump.

Swaying may help the rat figure out how far away various objects are. When a rat moves its head, the images of the objects around the rat move across its retina. Close objects will move faster than far ones, a phenomenon known as motion parallax. Rats may use such motion marallax cues to judge distance and depth.

For more on rat vision, see What do rats see?

2.7 Why does my rat carry its tail in its mouth?

A rat may pick up its tail in its mouth and carry it. Tail carrying is a rare behavior that has not been well studied and is not well understood. However, it may be a form of displaced maternal behavior. A nesting rat deprived of normal nesting material may carry her own tail and try to build a nest with it. A nursing mother rat may retrieve her own tail to the nest, like a pup.

3.0 Odd excretions

3.1 Why does my rat poop and pee when I pick it up?

A rat that poops and urinates copiously when picked up is frightened and stressed. Urination and defecation are common signs of stress, and may function to (a) void the animal of excess weight in preparation for flight, and in a prey animal such sudden excretion may (b) surprise or disgust a predator enough to drop the animal.

Humans do this too when extremely stressed or scared.

Rats may dab or smear drops of urine on the surfaces and objects they walk on, including yourself. This is called urine marking, or scent marking. Adult socially dominant males mark the most, but all adult rats, both males and females, scent mark to some extent. Females tend to scent mark most right before they come into heat.

Scent marking is a complex form of chemical communication that has several functions. It is a sexual signal that advertises the rat's presence to other rats of the opposite sex. Rats also use their own scent marks to denote areas that they have visited and are familiar with. Scent marking may help them navigate, too.

It is unclear whether scent marking serves a territorial function. If scent marking were territorial, then male urine should deter strange male rats from entering a marked area. However, this is not always the case: sometimes male urine attracts male rats. Therefore, it is unclear whether scent marking has a territorial function in rats or not.

3.3 What's that red stuff around my rat's eyes and nose?

The red stuff sometimes seen around a rat's eyes and nose is called porphyrin. It is produced by a gland behind the eyeball and helps lubricate the eye. Porphyrin naturally drains from the eye down into the nose through a small tear duct. Small amounts of porphyrin seen every now and then are normal.

However, when a rat is stressed, it may overproduce porphyrin, which may overflow the eyelids and form a red crust around the eye. Porphyrin may also overflow the nose, creating a red crust around the nostrils. This condition is called chromodacryorrhea and is a sign of illness or stress.

For more, see Those red tears: porphyrin and the Norway rat

3.4 Can rats vomit?

Rats cannot vomit: they cannot forcibly expel food from their stomachs. On very rare occasions, however, rats may regurgitate, which means that digested food may flow passively from the stomach back into the esophagus. Regurgitation is rare because rats have a very strong barrier between the stomach and esophagus.

For more, read Why rats can't vomit

4.0 Group living

4.1 Why are my baby rats chasing and jumping on each other?

Young rats chase each other, jump on each other, and pin each other to the ground. They are play fighting. Rats start play fighting at around 18 days of age. Play fighting peaks at around 30-36 days of age, then declines. In play fighting, the goal appears to be contact and defense of the rat's nape. If a rat succeeds in contacting an opponent's nape, he nuzzles it gently with his snout.

Play fighting is not a good predictor of adult dominance hierarchies: the winner of play fights may or may not become turn into the winner of real fights. Nor is play fighting necessarily "practice" for adult fighting, because the goals and tactics of adult fighting are different from play fighting. Therefore, play fighting and adult fighting are related but separate activities.

For more, see Play fighting in male Norway rats.

4.2 Why are my adult rats chasing each other, boxing, sidling, rolling on their backs and squeaking?

Rats reach puberty at around 5-6 weeks of age, but they reach social maturity at around 5-6 months of age. At this age, male rats in particular start to behave more aggressively toward each other. They shift from harmless play fighting into more serious adult fighting. The consistent winner of such interactions imposes himself on the other members of the colony. Humans describe this as as "becoming socially dominant." Once a dominance hierarchy is established, it may remain stable for a long period of time.

Adult fighting involves contact and defense of the rump. If a rat manages to contact an opponent's rump, he may try to nip or bite it. A rat tries to hide his rump from attack by running away. He may also stand and face the aggressor and maintain whisker-to-whisker contact with him (called boxing ), or by laying on the back to hide his rump. As long as a rat keeps distance, or his whiskers, teeth or body between the attacker and his own rump, he has a higher chance of preventing an attack.

To counter the defensive boxing strategy, the attacker may drop to all fours and sidle forwards, and thus reach around and inflict a bite from the side. To counter the belly-up strategy, the attacker may lay perpendicularly on top of the supine rat and try to dig under him to gain access to the rump.

Both domestic rats and wild rats fight using these strategies. However, because domestic rats are often confined to a cage, fights between domestic rats may escalate more because fleeing is impossible.

Fights may also occur between resident rats and a strange rat introduced in their colony. The resident dominant males presses most of these attacks, especially on male intruders. Females may also attack intruders. Aggression toward a stranger can be severe and sometimes fatal.

For more, see Aggression in Norway rats.

It is commonly believed among pet rat owners that when one rat urine marks another, he is claiming dominant status. This urine = dominance belief is probably incorrect because all rats mark each other to some extent. For example, juveniles mark adults, females mark males, males mark females, dominant males mark subordinates and subordinates mark dominants and each other. It is unreasonable to assume that all such marks are claims of dominance.

Urine marking of fellow rats is probably a complex form of chemical communication whose meaning depends on the identity, age, and status of the marking and marked rat. For example, females tend to urine mark aggressive males with high testosterone, possibly indicating that they prefer such males and would like to mate with them. Young juveniles copiously mark adults, who mark them right back.

The copious urine marking by dominant males of subordinate rats is probably a feature of his dominance, rather than a cause of dominant status. Through fighting and other behavioral strategies, the dominant rat has won the ability to impose himself on others. The dominant male can therefore crawl over everyone else and urine mark them with relative impunity. Subordinates cannot crawl over the dominant rat as frequently, but when they do manage to do so they deposit lots of urine on him.

Therefore, frequent urine marking of another rat is contingent on the ability to crawl over him. The ability to crawl over another rat depends on the rat's status, and the rat's status depends on the outcome of past aggressive interactions. Copious and frequent urine marking by the dominant male of other rats is therefore not a cause of his dominance, but an indicator or a consequence of his dominant status.

No.

Some rat owners advocate rubbing human urine on their pet rats in order to 'gain dominance' over them and thus (the theory goes) stop aggression between rats. This odd recommendation is known as the 'dixie cup method' because you're supposed to urinate in a small cup first. This recommendation stems from a misunderstanding of rat urine marking. It may also come from concepts borrowed from dog training literature on the controversial practice of 'gaining dominance' over pet dogs.

However, there is no evidence to suggest that dabbing your own urine on a pet rat will stop a rat's aggression toward other rats in the future.

For one, rat urine is a complex chemical signal that is intimately connected to the rat's biochemistry. Urine contains information about the rat's species, sex, age, reproductive status, social status, and stress level. This information cannot be faked. Humans produce human urine, not dominant rat urine. Rats have a sophisticated sense of smell and are quite capable of telling the difference.

Secondly, urine marking by a rat does not catapult that rat into dominant status. All rats urine mark each other to some extent: juveniles mark adults, females mark males, subordinates mark dominants. These different types of marking have a variety of functions, many of which have nothing to do with social dominance (e.g. adult marks serve as a sexual advertisement to the opposite sex). Therefore, the mere act of urine marking does not automatically confer social dominance.

Lastly, the copious urine marking by a dominant adult male is a consequence of his dominant status, not a cause of that status: a dominant rat copiously marks subordinates because he is dominant. The reverse notion, that rat becomes dominant by peeing on others, is false. Instead, rats create their social order by engaging in multiple aggressive interactions over time. A winner gradually emerges and seizes certain perks (best sleeping spots, most matings, best treats), including the ability to walk over others with relative impunity. All the rats walk over each other and deposit urine on each other's fur from time to time, but subordinate rats can't walk over the dominant rat as often as he walks over them, so the net result is that he marks them more often than vice versa. The winner's urine chemistry and copious marking therefore reflect this new social reality.

So, what happens if you dab your own urine on a rat? The rat will probably sniff it curiously. Other rats may come over and sniff it too. After all, it's a new smell. It's like you just handed them a book of personal information. Then they'll groom it off. Rats are clean animals; they don't like foreign stuff on their fur. End of story.

No.

The flip-and-pee method of "training" is advocated by some rat owners as a way to deal with rat aggression directed at the human owner or at other rats. Here is an example of the method taken from a pet rat owner's list. In this case, an owner had recently obtained a juvenile rat that was lunging and biting the owner's hands. After struggling and squealing during a handling session the new rat jumped from the owner's hands, ran right into another rat and attacked him. The advice given was:

Take a tip from your big dude rat...Show the little thug who is *really* in charge. [snip]. Put some of your urine in a cup and set it aside. Grab the little imp and flip him on his back, agressively scratch his belly and brush your urine on his nose and belly and sex organs... If he protests, yell:"NO!" and continue to hold him on his back. Release him. If he gets up fast, throw him on his back and hold him till he squeaks. When he gets up slowly, let him. Do this several times a day when you feel like it and especially if he gets nippy. [Ratlist, April 2003]

There is no empirical support for the flip-and-pee method of training. I'm not sure where the idea originally came from -- perhaps from the controversial method of "getting dominance" over an aggressive dog. The flip-and-pee method of rat punishment relies on deeply flawed ideas, such as:

As to whether the flip-and-pee method works, I hypothesize that a rat that is flipped over, held down, perhaps yelled at and rubbed with urine, would be startled into stopping what it was doing at the time and be cowed and withdrawn afterwards. Not because it was "put in its place" socially, but because it was surprised, diverted and perhaps frightened by the human's overbearing behavior. In other words, the flip-and-pee action might act as a garden-variety negative reinforcement, like an electric shock.

(For further thoughts on this topic, visit Thoughts on human and rat ethology )

4.5 Why do rats sometimes eat their babies?

Mothers, strange females, and strange males may commit infanticide, all for different reasons. Most infanticide is directed at newborn infants.

A mother may kill deformed or wounded infants, possibly so she can allocate resources to the healthy pups who are more likely to survive. A mother may kill her entire litter if she is stressed, thus recovering some of her energetic investment. Malnourished mothers may cannibalize their litters, possibly to balance their diets. A mother who has an abnormal birth experience, such as a c-section, may also kill her litter. Normal full-term labor and delivery through the birth canal may be important for triggering the hormonal profile that accompanies maternal behavior, and these may be disrupted with a c-section, leading to abnormal maternal behavior and infanticide. Mothers who are very young or very old may also commit infanticide.

Unrelated adult males may kill a litter to bring the mother back into heat faster so he can sire a litter of his own. Unrelated adult females may kill a litter to gain food and to take over the nest. In general, living with the mother reduces infanticide in other rats. Unrelated females tend not to kill the litters of females they've lived with, and may even participate in cooperative rearing. Unrelated males tend not to kill the litter if they've lived with the female during her pregnancy.

For more, see Infanticide in Norway rats.