Rodents
Mammals of the order Rodentia, with incisors (front teeth) that grow continuously and must be kept to a manageable size by gnawing on things. Because of this unique trait, making observations about the teeth of the rodent skulls in this station can be enlightening. Each pelt in this station has a corresponding skull, and there may be extra skulls or rodent parts such as quills.
Identifying your rodent pelt
The pelts are very fragile! Please handle them gently and treat them with respect. Open your field notebook to the pelts page.

Observations
Look at your pelt. What color is it? Are there different colors on different parts of the pelt? Is it large or small? Feel your pelt. Is the fur thick or thin? Is it coarse or fine? Record your observations in your field notebook.

Measurements
Measure the length of the body from the nose to the beginning of the tail. Measure the length of the tail. Measure from the foot to the shoulder. Record these measurements in your field notebook.

Identification
Look at the pictures in the mammal field guide. Find the picture of your animal. Use the guide to find the description of your animal. Do your measurements fit the description? If not, go back to the pictures and try again.

If your measurements fit, write down the name of your animal and use the description to fill in the rest of the blanks on your pelts page. Share your findings with the rest of the group.


Beaver
How does the beaver fur feel different than the other animals? Can you tell where the beaver spends most of its time by how it feels? (it feels slicker, more waterproof, so it lives in the water). The beaver pelt has a rich history in the Northwest (there is a beaver on the back of the Oregon state flag). Beaver pelts were valuable and were traded like money. One beaver pelt was called a "beaver dollar" and you could buy something like a blanket for three and a half beaver dollars. If everyone could go out into the forest and hunt their own money, what do you think happened to many of the beavers?
Nutria
A nutria has almost the same niche as a beaver. They look almost the same, but a nutria has a tail like a rat, instead of the wide flat tail of the beaver. Nutria were imported from South America to replace the declining beaver population. Nutria pelts were never as popular as beaver pelts, however so they were not hunted as much. You can tell that the nutria spends much of its time in the water because of the way the fur feels.
Skulls

The skulls are very fragile! Please handle them gently and treat them with respect. To avoid damaging the skulls, only place them on the rug or the fleece bag. Open your field notebook to the skulls page.

Look at the skull in front of you. What size is it? What general shape is it? Use your hands to sculpt the air and show what size you think the whole animal is. Compare your skull to your neighbors and make some observations about the similarities and differences.


Nose

Look into the nose of your skull. The more bony surface area there is inside the nose, the better the animal can smell. How does this compare with a human nose?
Teeth

Look at the teeth. Are there different types of teeth? Examine the shapes of the teeth. Use your tongue to find similarly shaped teeth in your own mouth.

Can you tell what the animal eats by what kind of teeth it has? Sharper teeth are used for cutting and tearing, flatter teeth are used for grinding and chewing. What happens if an animal with sharp teeth uses its teeth for grinding or chewing? (Domestic dogs are an example of this, their sharp teeth become dull from eating crunchy dog food. Puppies have not eaten as much so their teeth are much sharper).

Herbivores eat plants, carnivores eat meat, and omnivores eat both plants and meat. Which kind of animal is your skull?

The long sharp teeth are called canines. The teeth between the canines are called incisors. The teeth behind the canines (toward the back of the mouth) are the premolars and molars.

Count each type of tooth on your skull. Record your observations in your field notebook. Does your skull have any specialized teeth (such as really long incisors)? What could these teeth be used for? What happens if these teeth break or wear down? (Rodent teeth grow throughout their lifetime. They must chew on hard objects to wear their teeth down and keep them short).




Eyes

Find the eye sockets on your skull. Put your fingers through the back of the skull into the eye sockets to see which direction the eyes point. Do they point forward or to the sides? Record your observations in your field notebook.

What kinds of animals would want to see straight ahead? Why? Animals who hunt other animals (predators) need to focus on the prey that is in front of them.

This kind of vision is called binocular vision. Hold your hands up to your eyes like a pair of binoculars. Both eyes see the same thing from a slightly different perspective. This makes it easy to tell how far away something is.

What kinds of animals would want to see all around? Why? Animals who are hunted by other animals (prey) need to be aware of what is going on around them.

This is called monocular vision. Hold your hands up like binoculars again, but this time cross your arms. Each eye is seeing a different image. This makes it easy to see more of what is going on, but harder to tell how far away something is.

Hold your arms outstretched in front of you. With your index fingers extended and one eye closed, bring your fingers together and try to touch them to each other. Using one eye to view an image, distance is hard to gauge.
Muscles

The more surface area there is on the skull, the more places there are for muscles to attach. Is there a ridge along the top of your skull? This is called the saggital crest. The saggital crest is where the jaw muscles attach, the larger the crest, the stronger the jaw.

Feel the top of your own head. Do you have a large saggital crest? Why not? Now hold your hands on the sides of your head, just above your ears and make some chewing motions. What do you notice?

What kinds of animals would need a strong jaw? Why?

Look carefully at your skull, and compare it to the skull plates in the field guide. Can you tell which species it is? Read about your animal and fill in the information on the skulls page of your field notebook.




Ways to demonstrate depth perception

When you use two eyes to view the same object at the same time, you can tell how far away the object is. This is called "depth perception." Depth perception is useful for animals who hunt.

As humans, we are so used to processing this kind of information instantaneously that we take this skill for granted. Show your students what it is like to only use one eye - or what it is like not to have depth perception.

The finger method - Hold your arms straight out to the sides and point your index finger forward on each hand. Now close one eye. Bring your arms forward and try to make your two index fingertips touch. With one eye closed, it can be difficult to be accurate.
The shrinking hand - Hold your hands side by side a couple of feet in front of your face. Close one eye and slowly move one hand closer or farther away. The hand will look like it's growing or shrinking, but won't really look like it is a different distance from your face.

Playing catch - Find the depth-perception ball in the skulls box. Play a few rounds of a relaxed game of underhand catch with a student. Throw the ball back and forth enough times that the student can consistently catch the ball.

Now have the student close one eye. This time when you throw the ball, don't throw it to the student, just throw it straight up in the air and catch it yourself. The student will try to catch the ball, even though it is nowhere near them. This demonstration only works once, even though many students will want to try it.