Article: What makes a rodent a rodent?

Tequila, the pet mouse, peeks out of a "log"

I take my pet capybara Caplin everywhere. She goes out to lunch, to various flooring stores looking for new vinyl for the laundry room, to get new tires on my truck, to buy paint brushes. It’s surprising how many places you can take a capybara, maybe because she’s so unusual and people just don’t know what to think.

Wherever we go, Caplin gets a lot of attention. People want to know what she is. Of course, “capybara” doesn’t mean much so I have to further explain that capybaras are the world’s largest rodent. “Oh,” many people respond, “a giant rat.” I don’t have anything against rats, they’re smart, cute and they make great pets, but Caplin is not a rat. Nevertheless this common reaction led me to wonder exactly what it is that makes a rodent a rodent.

Over one quarter of all mammal species are rodents and several rodent species are commonly kept as pets. A hamster or a gerbil is often a child’s introduction to the responsibilities of pet ownership. When I was growing up we kept guinea pigs. Other rodents are prairie dogs, nutria, groundhogs, squirrels, marmots, gophers, beavers, lemmings, chinchillas, chipmunks and porcupines.

Most rodents are very social and very vocal, although much of their vocalization is outside the range of human hearing. The prairie dog is thought to have the most sophisticated animal language known. Naked mole rats, such as the one depicted in the cartoon “Kim Possible,” are the only eusocial mammal. Like ants and termites, naked mole rats are born into “castes” for which they develop unique physical traits. There is a colony of naked mole rats at the Houston Zoo and it is well worth a visit.

The main identifying characteristic of rodents is their teeth. Rodents have four very large teeth at the front of their mouths, two on the bottom and two on the top. These incisors grow throughout their lives and rodents must gnaw on things to wear them down. The teeth retain their edge due to a natural sharpening process. Thick enamel on the front but not on the back results in a wear pattern that constantly sharpens the teeth. Note that although rabbits have similar looking teeth, they are not rodents and belong to the Lagomorpha.

Another characteristic of rodents is that they are able to digest cellulose, the tough polysaccharide that makes up plant cell walls. They do this through a symbiotic relationship with bacteria. Rodents have a specialized adaptation of the large intestine called the caecum where cellulose digestion takes place. Because cellulose breakdown occurs in the large intestine while absorption takes place in the stomach, rodents first eliminate the partially digested plant material in the form of pellets. The rodents then practice coprophagy which entails eating the passed pellets and returning them to the stomach for further digestion.

Most rodents are herbivores although rats and mice are omnivorous and a few species are specialized carnivores. The large incisors can be used to crack open seeds, cut tough plant stalks (in the case of beavers this even includes trees) and gain access to well-hidden human food stores.

Rodents association with food supplies and their ability to carry human disease has probably led to much of their negative image. It is common knowledge that the “Black Death,” the great bubonic plague epidemic that led to the Industrial Revolution, was spread by fleas that spent part of their lives on rats. Recently hanta virus has given the adorable prairie dog a bad name. On the bright side, rodents neither get nor carry the rabies virus.

I’m not sure how any of this information is going to help me explain Caplin to people who meet her. I’m sure they’re not going to want to know about the disease or the coprophagy aspects of rodent life. Maybe I’ll just mention she’s related to beavers. Or chipmunks, who can resist those little cuties?

Photo: Tequila's babies at the "hopper" stage.Photo: Caplin the capybara demonstrating the distinctive rodent teeth.
Photo: Prairie dogs, like this one from Big Spring, TX, have a complex social system and a language to match.
Photo: This groundhog lived in a burrow in a cemetery in Maine.
Photo: Chipmunks, or ground squirrels, are brightly colored and cute. This one lives in Yosemite National Park in California.
Photo: Squirrels, like most rodents, are herbivores. This one is eating a pear from a tree in my backyard.
Photo: There are more species of rodents than any other mammals. Notice this squirrel from Yosemite National Park looks quite different from the one from Texas.

Article: The cutest rodent in the world

Close-up of a baby capybara named Caplin

I’m writing this article with a capybara sleeping on my lap. Capybaras are the world’s largest rodents with adults reaching 150 pounds. Caplin weighs about four pounds but she’s only fifteen days old. She has already doubled in weight since she was born.

Caplin is my new pet but she’s not the only pet rodent to have inhabited this house. When my daughter was a teenager she had a pet rat named Rainbow. Properly treated and maintained, rats make excellent pets. They’re smart, clean and personable. They can identify people and can learn tricks.

Capybaras don’t look like rats, they look like another rodent commonly kept as pets, guinea pigs. Capybaras have big, square heads, short bodies and no tails. Also like guinea pigs, capybaras are native to South America. They range from Panama down the eastern side of the continent. Unlike guinea pigs, capybaras are semi-aquatic. They have partially webbed toes to allow them to move easily on moist or muddy ground.

My kids and I went to the Los Llanos region of Venezuela earlier this year. We saw hundreds of wild capybaras sitting on the roads, wading in the swamps or swimming in the multitude of lakes. The setting looked idyllic but life in the wild is hard for capybaras. They share the swamps with caiman, crocodiles and anacondas all of whom enjoy a delicious meal of capybara. Those are some fearsome predators. And that’s not counting the occasional jaguar.

Of course, the wild capybaras main threat comes from humans. In addition to the standard issues of habitat destruction, capybaras are also hunted. This hunting is exacerbated by the fact that capybara are considered legitimate to eat by Catholics during the forty days of lent, the only mammal to have that honor. During our stay in Los Llanos, our guide told us that capybaras in that area are only eaten during lent and hunting is prohibited the rest of the year, but this is probably not true throughout their range.

Capybara gestation takes between five and six months which seems like a long time for a rodent. A typical litter contains five babies who are born with fur and with their eyes open. In the wild, baby capybaras stay with their mothers for up to eighteen months. Even though they nurse, baby capys eat grass from their first day of life.

Pet capybaras are not easy to come by. We searched the web and could find only one breeder in the United States, fortunately located not too far away in south-western Arkansas. When we contacted her we found she didn’t have any babies for sale and that her sales were booked for many litters in advance. Luckily she pointed us to one of her previous customers who had just had a litter. His location in Nacogdoches was fortunately even closer. By the time we got there less than a week later, only one of the original five babies remained.

We’ve had Caplin five days and can already see she will make a great pet. She loves being scratched or having her ears rubbed. She litter box trained herself. She’s still a bit skittish when she thinks someone is going to catch her but otherwise she will climb all over you, chew on your hair and take food or a bottle from your hand. When she’s happy she makes quiet chirping or purring sounds, more high-pitched than a cat’s.

The large size of a mature capybara probably means Caplin will have to move out to the backyard when she gets bigger. I’m hoping she’ll help with the mowing and maybe even cut back on the plants growing in my pond. Cute, friendly and useful, capybaras make the perfect pet--I hope.

Here’s a link to a YouTube video of Caplin getting her chin scratched.
http://www.youtube.com/watch?v=leBCilpEqbY&NR=1

Photo: Caplin sitting under a chair.

Photo: Caplin on the couch.
Photo: Coral holding a wild baby capybara in Venezuela. At night you can pick them up when they're sleeping on the road.
Photo: A capybara family swiming in Los Llanos.
Photo: When two capybaras meet, their birds swap places.