Rodents
Rodentia
INDEX
WHAT ARE RODENTS?
RODENT FEATURES
TYPES OF RODENTS
RODENTS OF THE BAHAMAS AND CONSERVATION
RODENTS OF ARDASTRA
WHAT ARE RODENTS?
Of the 4000 species of mammals existing today, over 2000 belong to the order Rodentia. Most people are familiar with mice, rats, hamsters and guinea pigs but the rodent order also includes beavers, muskrats, woodchucks, prairie dogs, squirrels, chinchillas, and many others.
Although fossil records show that rodents first appeared about 50 million years ago, more than half of the species of rodent existing today did not appear until 5 million years ago. Rodents are very successful have an amazing ability to adapt to almost any environment and they produce large litter sizes quickly, in relation to most mammals.
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RODENT FEATURES
Despite their morphological and ecological diversity, all rodents share one characteristic: their teeth, which are highly specialized for gnawing. The name Rodentia actually comes for the Latin verb rodere meaning “to gnaw”. Rodent mouths are equipped with two upper and two lower incisors (front biting teeth), followed by a gap called the diastema, followed by one or more molars or premolars (crushing teeth). The number of molars and premolars is determined by the species. The incisors of all rodents are rootless, growing continuously through life. The front surfaces of the incisors are covered with hard enamel while the back surface is not. During gnawing, the incisors grind against each other, leaving the enamel edge as a blade. Rodents often grind their teeth together to keep them in good condition. This "self sharpening" system is very effective and is one of the keys to the rodents’ great success. The main muscle used in chewing is the masseter, and rodents are divided into several different groups based on exactly how they use these muscles.
Rabbits are often referred to as rodents; this however is not the case. Rabbits, hares and pikas make up the order Lagamorpha that differs from Rodentia in that they have an extra pair of upper incisors.
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TYPES OF RODENTS
Rodents are divided into three main groups;
- Squirrel-like rodents - (Sciuromorpha) - includes the squirrels, chipmonks, marmots and prairie dogs.
- Mouse-like rodents - (Myomorpha) - includes rats, mice, hamsters, voles, lemmings and gerbils. This is by far the largest family of mammals.
- Porcupine-like rodents - (Hystricomorpha) - includes the mole rats, porcupines and capybaras.
Through human introduction their distribution is almost worldwide, with habitats that are quite varied. Some rodents are fossorial (specialized for underground life like the gopher), others are aquatic (living in the water), arboreal (living in trees), or terrestrial (ground dwellers). Some move by leaping, others by running, some can glide while others are swimmers. Rodents can range in size from pygmy mice weighing 5 grams to capybaras weighing over 100 pounds.
RODENTS OF THE BAHAMAS AND CONSERVATION
Today, rodents can be found throughout most of the Bahamas but most of these were brought by man, including the Norway rat, Roof rat and the House mouse.
There is one species of rodent that is native to the Bahamas, the Hutia. The Hutia, along with bats, are also the only land mammals native to the Bahamas.
Bahamian Hutia - Geocapromys ingrahami
ENDANGERED SPECIES
Hutias are in the Porcupine-like rodent group and form a large family of about 20 different species called the West Indian hutias. These are found throughout the islands in the West Indies, with the greatest diversity on Cuba.
The Bahamian hutia belongs to a group known as the Ground hutias and they are found on islands in the Bahamas with some subspecies also on other islands of the Caribbean, and northern Venezuela. These rodents are found in forest habitats in the Bahamas, in the trees or on the ground. Hutias were once found throughout the Bahamas but today they are mostly found on the eastern island of the Plana cays.
Hutias are nocturnal animals (awake at night) and are mostly vegetarian, feeding on bark, leaves, nuts, fruits and the occassional insect or lizard.
The Bahamian hutia tend to live in pairs but they are quite social with other hutias too. They are not aggressive, often playfully wrestling with each other. Both the males and females employ scent marking with urine, not to mark territory but rather to ensure that the group sticks together.
The Bahamian hutia is considered an endangered species and is protected under the Wild Animals Protection Act of 1968. Once common throughout the Bahamas, these rodents were known to be a favorite food of the native indians and they were continually hunted by the early colonialists. These colonists brought with them dogs, cats, raccoons, rats, pigs, donkeys etc, which have also contributed to the depletion of the hutia populations to near extiction. Further more, the Bahamian hutias are in danger of becoming extinct as there is very little genetic variation between them and this makes them vulnerable to disease. In fact, the Bahamian Hutia was thought to have been extinct until 1966 when Dr Garrett Clough visited the Plana Cays and now they are consicered to be "living fossils". Today the population of the hutia on East Plana cay is a healthy 5,000 - 10,000 individuals and there have been experimental relocations of the species to other islands in the Bahamas, namely in the Exuma cays. This introduction has gone exceptionally well and has unfortunately had a negetive impact on the island as the hutias have out populated the available food resource and have depleted the island of many plant species.
RODENTS OF ARDASTRA
Ardastra has a number of rodent species; Prairie dogs, squirrels and capybaras.
Black-tailed prairie dog - Cynomys ludovicianus
Prairie dogs are close relatives to the ground squirrels, chipmunks and marmots. They come under the genus Cynomys, which is a Greek word meaning "mouse dog". There are five different species of prairie dog which inhabit the short and medium grass prairies and plateaus of Southern Canada and Montana, Western United States, all the way to Northern Mexico.
- Black-tailed prairie dog - (Cynomys ludovicianus) - central Texas in the south to just north of the Canadian/United States boundary.
- White-tailed prairie dog - (Cynomys leucurus) - Colorado, Utah, Wyoming, and Montana.
- Gunnison’s prairie dog - (Cynomys gunnisoni) - Utah, Colorado, New Mexico, and Arizona.
- Utah prairie dog - (Cynomys parvidens) - Southwest area of Utah.
- Mexican prairie dog - (Cynomys mexicanus) - within parts of Mexico.
Prairie dogs are extremely friendly and social creatures; one will often see them huddle in groups cuddling, hugging, grooming and playing. They live in a series of burrows and tunnels called "towns". These towns are divided into wards that are made up of several social units called "coteries". Coteries commonly consist of 1 male, 1-4 females and their offspring (under 2 years of age). The females usually share the responsibility of raising the young. Prairie dogs breed just once a year and yeild about 3-4 pups. In the wild the average life span is 3-4 years but in captivity they can live to at least 8.5 years of age. Ardastra has had a prairie dog live up to 11 years of age!
The largest prairie dog colony ever reported was in Texas, 100 by 250 miles, containing approximately 400 million prairie dogs. However, despite these outrageous quantities, the Black-tailed prairie dog population has dropped severly and are disappearing rapidly due to eradication by local state and government, devestation from disease, poisoning, recreational shooting and habitat destruction. They now occupy less than 1% of the land they occupied a century ago.
The destruction of these animals is due to common myths about them, such as they are a menace to domestic livestock and farming, they spread the plague, and because no one would miss them. In reality, cattle and Prairie dogs have a mutually beneficial relationship: Prairie dogs improve rummage as they are natural fertilizers which increases the protein content and the digestibility of rangeland grasses and in return, the grazing areas provide good homes for the prairie dogs.
Prevost's squirrel - Callosciurus prevosti
All squirrels are characterized by their relatively primitive jaw structure. There are three basic body forms in squirrels: tree squirrels, ground squirrels and flying squirrels.
- Tree squirrels - have long, bushy tails, sharp claws and large ears. Some have well-developed ear tufts.
- Flying squirrels - have a furred membrane (patagiuim) extending between the wrist and ankle that allows them to glide between trees.
- Ground squirrels - are generally more robust than tree squirrels and often have short, sturdy forelimbs that are used for digging. Their tails, while fully furred, generally are not as bushy as those of tree squirrels. Like many other rodents, all squirrels have five functional toes on the hindfeet and four on the forefeet, with a well-developed claw on each digit.
The Prevost’s squirrel belongs to the tree squirrel group and is one of the fifteen species included in the genus Callosciurus, which means "beauitful". Actually, the Prevost's squirrel is often called the beautiful, ornamental or tri-colored squirrel. These names are very fitting as they are among the most brilliantly colored of mammals. They can be found in a few Southeast Asian countries and many small islands of the East Indies. Being largely arboreal (tree dwelling), Prevost’s squirrels inhabit trees of the middle and upper story of lowland montane forests. These crepuscular (active mainly during dusk and dawn) squirrels either nest in tree hollows or make nests of leaves and twigs. Diets do vary throughout species range but include many fruits, nuts, seeds, buds, flowers, and other vegetable matter. They will occasionally supplement their diet with insects, larvae and bird eggs. The breeding season of the Prevost’s squirrel is year round; females having up to 5 young. Currently this squirrel is not threatened. However, habitat destruction and the pet trade may begin to affect their numbers in the near future.
Capybara - Hydrochaeris hydrochaeris
The capybara is the largest member of the order Rodentia. The females can weigh between 80 - 145 pounds and the males average slightly more. There is but a single living genus and species, Hydrochaeris hydrochaeris, which is native to Central and South America, particularly in the Amazon rain forest, Panama, the Andes Mountains, Colombia, Uraguay and Argentina.
Being semi-aquatic (living on land but highly adapted to water life), the capybara thrives in densely vegetated areas around ponds, swamps and marshes. They spend most of their time either nursing or feeding on an array of vegetation, including aquatic plants, grasses, tree bark, grains, melons and occassionally other fruits; selecting vegetation with a high protein content. With long, course pelage (hair) that is very sparse, a large stout body and webbed toes, it is specially designed for its aquatic habitat.
Highly social animals, capybaras live in groups controlled by a dominant male. These rodents are also mainly crepuscular, resting during the heat of the day in a shallow burrow in the ground. If threatened on land, they can run like a horse. When a predator is close, they will slip into the water to escape. While swimming, only their nostrils, eyes and ears stick out of the water. A capybara can dive and remain underwater for several minutes.
The males and females can be distinguished, as the male has an enlarged scent gland on top of his snout, called a morrillo. The females also have this but it is less pronounced. The capybaras use this gland as a means of scent identification and the males will also mark their territories with the scent produced by this gland.
With sexual maturity being reached at 15 to 20 months, a year round breeding season and an average litter size of 3 to 4 babies, the capybara does well as a species. Adult and juvenile capybaras are preyed upon by anacondas, caimans, jaguars and man. The capybara is also farmed commercially, mainly for meat and leather, but their fatty skin is also used as a grease in pharmaceuticals. The ranching of capybaras has an ecological importance as large areas of wetland is preserved, which would otherwise be drained for the ranching of cattle.
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