Rodents

Rodentia are the largest order of mammals in the world, encompassing over 40% of mammal species.  A rodent is characterized by having two pairs of large front teeth, one pair in each of the upper and lower jaws.  These are called incisors and are used for gnawing vegetation.  They have no canine teeth, leaving a large gap between the four front teeth and their molars in the back of the mouth.  Rodents can be found in all types of habitat everywhere in the world except Antarctica, New Zealand and a few oceanic islands.

The largest rodent is the capybara, Hydrochoerus hydrochaeris, growing up to 140 pounds.  But a majority of species are small animals, under 4 ounces, with bulky bodies, short limbs, and long tails.  Compared to their overall size, the body’s surface area is large and contributes to a greater loss of heat than larger animals.  To combat this, rodents create more body heat by being constantly active.  They consume large quantities of food to meet high energy needs.  Many species are active year-round, coming out during early morning and late evening hours to feed.  Animals living in habitats with extreme temperatures may hibernate to escape the cold or estivate to escape the heat.  These species conserve energy by adjusting their body temperatures to within a few degrees of the air temperature and slow other bodily functions, requiring less food and more rest.

Incisors grow constantly their entire lives.  The front surface is protected by a hard enamel shell.  The back surface of the upper pair is soft and easily wears away from the constant rubbing of the lower teeth as vegetation is bitten off and chewed.  This creates a chisel like edge on the top teeth that is an excellent cutting surface.  Teeth are used to gnaw vegetation, dig burrows, and for defense, if attacked.  If an animal does not gnaw enough vegetation, the growth rate of the teeth becomes greater than what is being worn away and health problems can develop leading to the inability to eat.  This most often occurs in captive animals who are not provided with sufficient quantities of harder vegetation.

Food is mainly seeds, leaves, fruit and small invertebrates or insects.  A internal structure called a caecum contains bacteria that assists in breaking down plant material into digestible form.  Several rodents have eyes that protrude in a half dome from their head allowing them to see both ahead and behind.  This wide field of vision allows the animal to easily detect predators.  Their daytime eyesight is poor, but they can detect ultra-violet light, allowing excellent vision during twilight hours when they are most often active.  Most rodents live in large social groups, but forage individually, using a wide variety of alarm calls to keep others informed when danger is near.

Humans often consider rodent species to be harmful pests.  While they may carry bacteria and cause nuisance problems, they are also beneficial by eating weed seeds and insects, keeping populations of many pest species in check.  Rodents are widely used in human culture as food, clothing, pets, and laboratory animals for research.  Visit a museum or nature center to learn about the many fun facts of each family in this amazing group of animals.