behavior

Rat-Sense

A rat’s senses are very unique and definitely worth a closer look. Ever wonder what your rat sees or how their sense of touch works? Ever want to know if they really do have a sophisticated palette or if they can hear in frequencies that we cannot? This is by no means a complete understanding of it, but it should help give you a glimpse. Maybe you will even want to do more research yourself. If so, let us know what you find out!

Sight

How do rats see? Rats can see only two types of color (blues and greens) compared to the human's three types (reds), but they can also see in some of the 'blue' spectrum that humans cannot, the ultraviolet. Rat's vision is called dichromatic but technically includes a bit more due to the ultraviolet range they can also see in. It is thought that rats developed the ability to see in this spectrum because this type of light is most abundant in dawn and dusk hours, when rats are most active. But this is only the color sensing part of vision. Another important thing to consider when talking about vision is light and dark perception, especially with rats, who take their cues from brightness over color. A rat's vision is blurry because of the lower number of cones present in the rat's retina. These cones are what lends to sharper vision. Rats only see slight clarity of an object up to a few feet away, and an item must be within 7cm to be truly visible. However, the placement of a rat’s eyes on either side of the head allows a rat to have a large field of vision, which is an obvious benefit to a prey animal. This placement also affects depth perception and is another reason why those whiskers come in handy! One trick rats use to gain better depth perception is called motion parallax. We’ve all probably seen our rats do this, especially if you have those with lowered visual capabilities (i.e. albinos). They sway their head from side to side to determine the relative distance of objects. There is some orientation visually, but most is accomplished by using the whiskers to touch as well. An albino rat's vision is worse, and deserves a couple more comments. The iris of a albino rat's eye is unpigmented (the pink color comes from the capillaries and blood present in the eye), so it cannot block incoming light. Therefore, what they see is a washed, patchy, light and dark image versus one with somewhat defined edges. The inability to filter out light also makes the retina degenerate quicker. In fact, if a rat is in 24 hour light, the degeneration can occur in as little as a few weeks, which is yet another reason to be sure and offer normal cycles of light and dark for our rats. In bright light, a pink eyed rat is virtually blinded, and they take longer to adapt to dark environments as well. Depth perception is poorer too. As a side note, vision is also impaired with age, so older rats do have lower visual capacity than younger rats.

Taste

How do rats taste? Wait, that doesn't sound right, does it? Anyways, for rats, taste is all about function. They need to make sure that foods are safe to eat, so rats use a sampling technique to test small bits of new foods to be sure they are edible. When something is put into the mouth, saliva dissolves it and stimulates the taste buds to detect salt, sour, sweet, bitter, or umami. The taste is relayed to the brain to produce a behavioral response, from feeding to avoidance. Food preferences and safe associations are formed in interesting ways sometimes. One example is that foods eaten by the mother will be preferred by the pups as tastes are transferred by the milk. Associations are made to avoid certain foods too. If an individual ate an item that made it ill, it will avoid. Or, if socially, other rats are either eating or avoiding a food, so will others in the group. Maybe that's why none of my rats eat frozen carrots, but I digress. Social acceptance of items can also come from the people that rats trust!

Smell

How do rats smell? I know, I know.. it depends on who you ask.. corn tortillas, grape soda, piddle. But how they use their sense of smell is extremely fine tuned, and the world of smells to a rat is very unlike ours. Rats also use scent to learn, and they can tell the difference between odors, both food and other rats. You may notice your rat sniffing deeply at a surface once in a while. When they do this, it appears they are pressing their nose right into what they are smelling. They are actually using a secondary scent organ, the vomeronasal organ, to pick up molecules of scent. This organ is used to smell pheromones, which are most concentrated in urine and other body secretions. It is this chemical scent that tells a rat everything they need to know for mating, social order, health, gender, age, and more. Urine marking then becomes an important part of rat behavior since the urine leaves these chemical cues in the environment the rat is in. In regard to sexual behavior, pheromones also contain cues for other members of a group. For instance, the presence of female pheromones results in the delay or suppression of estrus cycles, where male pheromones speed up the puberty and stimulate estrus cycles in mature females. Behavior in rats is largely affected by scent, but this is not limited to mating. Aggression, mothering, and food selection are also affected. As a side note of interest, albino or pink eyed white rats tend to have a lower sense of smell.

Hearing

How do rats hear? Rats have hearing that is much more sensitive than a human’s. They hear softer sounds and can hear into the range of ultrasonic too. Where we can only hear up to 20kHz, rats can hear up to 90kHz! In fact, most of the vocal communication that rats use is above or below what we can hear. When a rat is in distress, for example, it vocalizes in the high range around 20-50kHz, which is just barely audible to us. Most people have witnesses rats boxing, and sometimes, it is accompanied by one or both rats having their mouth gaping open to show the teeth, but no obvious noise is heard. In fact, there IS a sound, and if you listen close enough, a constant, high-pitched whine can be heard. These are also the types of whines made by rats in pain or under stress. Shorter, even higher pitched vocalizations are usually used for positive situations and have even been recorded during play, eating, and mating. In fact, research has been conducted to show that rats even ‘laugh’! Some of a rat’s hearing also involves the whiskers, which resonate like a tuning fork with certain frequencies of sound and depending on the length of the whisker, they will help interpret the sound. It is actually this fine sensitivity that helps rats to use their whiskers in the way they do, allowing a very detailed ‘picture’ of objects within physical reach. Of course, this means that rex or hairless rats have a lowered ability to detect fine textures and may interpret their environment a bit different from a standard rat.

Touch

How do rats feel? Apart from saying they feel soft and warm, the rat’s sense of touch is really quite significant. The sense of touch is through the whiskers and other sensitive hairs on the body mainly, and is the primary source for navigation. Whiskers are actually on the rat’s cheeks, chin, mouth, eyebrows, and even on the feet. They are more sensitive than a human’s fingertips and allow the rat’s surroundings to literally be ‘seen’ in sharp detail. Each and every whisker bends when it is touched, and those delicate movements are picked up by nerves that send detailed messages to the brain. The rat can even tell the direction and amount of movement in each separate whisker at any given time. Rats have whiskers when they are born, and within the first two weeks, they are whisking them back and forth like their adult counterparts. If a whisker is shed or lost, a new one will grow back in about a week, and until it is replaced, those around the lost whisker compensate for the loss. The brain is remarkable with how it can continue to function with the loss. However, if a rat has no whiskers, it's brain is actually abnormally wired and orientation within an environment is less efficient. How do rats use their whiskers? The whiskers are constantly whisking back and forth (average of 7 times per second) to perceive their immediate surroundings. Slower sweeps are made while exploring, and more rapid sweeps are typically seen when a rat is sitting still. Rats can even move whiskers individually and in opposite directions from one another. They can also point whiskers forward as far as 2 inches beyond their nose. They are truly remarkable features! Whiskers give a rat a three dimensional view of their close environment, down to detecting the difference in grains of sandpaper even! The whiskers resonate, and vibrations even help the rats 'hear'. Whiskers are used for balance, orientation, and depth perception. Amazingly, without whiskers, a rat in water would drown (please don't ask about the study that determined that one). The whiskers help the rat feel when the nose is above the surface of the water. Whiskers are used with contact, as well, and many aggressive rats that stand off to each other will maintain 'whisker' distance as a safety zone. All in all, a rat without whiskers is more impaired physically and behaviorally than a blind or deaf rat. So what about rex rat whiskers then? Rex coated rats have roughly half the whisker span that standard rats do, and in some areas like the top of the head, there can be an absence of functional whiskers all together, creating a 'blind spot'. A rat born with these shortened whiskers will adjust though, and are still able to 'feel' their environment in the same manner as a standard rat, but with obvious closer proximity, so it is limited. And rats with no whiskers are 'blind' to their world in a very unnatural way.

References available upon request.

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