Mammals That Gnaw (1974)

[Music] [Applause] most of the mammals that inhabit our Earth are rodents mammals that [Music] gnaw they're easy to tell apart from other mammals they're usually small and they have long curved front teeth that grow throughout their lives these inzer teeth are not only shaped differently from those of other mammals but they're also constructed differently the front surfaces are hard enamel the back surfaces softer Dentin as the the teeth are used softer dentine wears down faster than the harder enamel and a chisel-like shape is maintained continual growth makes up for the continual wear and the other way around the continual wear keeps them from growing too long when you compare the teeth of the gnawing mammals with those of the hoofed mammals the difference is easy to SP the enzers of a deer are small the MERS in back are larger these are used for grinding up the grass and leaves that a deer eats the MERS and the meat eating mammals are sharper and the canines not the front in sizers are long and sharp these are used by the meat eaters for tearing flesh but notice as we move the jaw of a gnawing mammal that the front incizors are longest their chisel-like shape is suited for getting at particular kinds of food in their diets kangaroo rats eat seeds squirrels gnaw holes in the hard shells of nuts to get at the food inside [Music] but the most common foods for most gnawing mammals are CHS grass and other [Music] plants some rodents will eat almost anything some eat berries some mushrooms and a few eat insects and other small animals whatever the rodents die each food Gathering trip is dangerous because most rodents are small there are always larger meat eaters around Hawks and Eagles thrive on rodents so snakes and some mediumsized meat eating mammals too so the gnawing mammals are usually secretive animals they stay close to home and that home is usually a place fairly safe from predators many like the woodchuck burrow in the ground so to prairie dogs who live together by the hundreds in enormous networks of tunnels [Music] many kinds of mice build their nests in Grass others like the packrat use grass and other materials to line their nests in rock [Music] crevices some take to the trees because of their sharp claws squirrels are well adapted for climbing and so many make homes in trees some in natural holes others in nests they construct of twigs and leaves some gnawing mammals smaller than squirrels like this deer mouse also live in trees so do larger ones like the porcupine unlike most rodents which depend upon Escape for survival the porcupine carries an effective defense around with it muskrats and beavers build lodges in the water to keep out of the way of predators but eventually each animal must come up from its burrow or down from its tree or back to the shore for food and when it does it exposes itself to danger to help warn them of approaching danger the rodents have a number of Highly developed senses most depend upon extremely sensitive hearing to make them aware of danger others use their sense of smell few of them have very sharp Vision however like other mammals that are also prayed on by Meat heaters the Nars have eyes so placed that it's possible for them to see danger coming from almost any direction without moving their [Music] heads Darkness helps hide those that feed at [Music] night their large eyes and Keen sense of smell make it possible for them to maneuver in dim light Darkness hides them from some Hunters but not from those that hunt in darkness most rodents that feed during the day are hidden by their small size and coloration some rodents use warning signals to tell others of danger prairie dogs signal with a chirp likee bark that's why they're called prairie dogs beavers slap their tails on the water other beavers hear this and dive below the surface for safety Chipmunks chirp a danger signal there are other adaptations that help protect them from predators chipmunks have special cheek pouches that can be stuffed with large amounts of food which reduces the number of dangerous food Gathering trips food can then be taken home to be eaten or stored in safety the habit of putting food away for a later meal is more common among the gnawing mammals than among any other mammals except humans squirrels are well known for burying and hiding [Music] nuts whether they actually remember where they've hidden them or just sniff them them out is [Music] questionable many nuts in the ground are forgotten and Sprout into [Music] trees pine squirrels gather cones packrats are great collectors that's where they get their [Music] name and the beavers cut twigs and saplings to take to their lodges they anchor these on bottoms of streams for use as food in the winter storing food makes it possible any of these small Plante eating animals to remain active during the cold months when food is normally [Music] scarce the rodents have learned to eat the food human store hundreds of millions of dollars worth of crops are destroyed each year by rodents some rodents carry disease the spread of plagues has been blamed on the black rat most rodents reproduce quickly partly for this reason the gnawing mammals are important AIDS in scientific studies they're used in research on nutrition behavior and Medicine and they're even kept as pets if any one word could be used to describe the gnawing mammals it is successful they have managed to spread to and thrive in almost every part of our Earth from deserts to much colder climates some live in high mountains and some tunnel most of their lives beneath the ground only a few are fairly large for example the Capi Vera in South America May weigh 200 lb but most rodents are [Music] small in kinds and numbers however the mammals that gnaw far outnumber all the other mammals on our Earth oh