A Little Bit More
Don’t get the idea that the air trapped in a Muskrat’s fur keeps it from losing heat, it doesn’t stop all heat loss. But it does greatly reduce the rate of heat loss and makes it possible for a Muskrat to forage in the water for an extended time. Muskrats are large rodents, most closely related to voles, lemmings, and deer mice. Although they look very much like small Beavers, they’re in a different rodent family.
Muskrats prefer water with an abundance of aquatic vegetation. They’re mostly nocturnal and feed largely on plant roots, bulbs, stems and leaves of cattails, bulrushes, sedges, lilies and pondweeds but will forage beyond the water if necessary. Piles of damp vegetation heaped up in shallow water up to about 2 meters high are the most obvious sign of their presence. Not all of these are houses, however as many serve as feeding stations around their territory. Although many muskrat houses are comprised of a pile of vegetation, in many farm ponds where there is no shallow water, they burrow into the bank to excavate dens. In winter, several Muskrats may retreat to a single den where their body heat can keep them as much as 20°C (68°F) above the outside winter temperature.
Muskrats swim buoyantly at the surface, propelled by powerful strokes of their hind feet. Their laterally flattened tail (Beaver’s tails are flattened dorso-ventrally) provides some propulsion and also acts as a rudder.
Note Muskrat's fur
Mink are probably the Muskrat’s most important predator, but River Otters, Coyotes, Red Foxes, and large owls and hawks also prey on them. Both sexes have musk glands at the base of the tail and use this odor to communicate with others of their kind. Strategic “hauling-out” places are liberally covered with musk either to intimidate intruders or to advertise the availability of females. Their musk has such long staying power that it has even been used as a base for perfumes.
Activities
Cold Hand/Warm Hand
Objectives: Experience why animals need to be insulated from water
Materials: Bowl of water at room temperature, thermometer (optional)
This is a very simple, straightforward exercise, but one I think is well worth doing. We all know how quickly water can rob us of heat, it’s just that we need to have it “spelled out” a little more slowly so we own this concept.
Water not only has a high heat capacity (ability to absorb a great deal of heat) but it also is an excellent conductor and can do so quickly. Endothermic (warm-blooded) animals, like the Muskrat, that live in water must do something to reduce the potential amount of heat loss when living in a wet environment. Not all mammals have the same strategies, but for those that have lots of hair, air trapped by hair provides an excellent way to insulate them from the heat-robbing water they live in.
1. Place a large bowl of water on a table in an out-of-the-way part of your room.
2. Allow the water in the bowl to reach the same temperature as the surrounding air (you can take its temperature to be sure that both the air and the water are the same temp or just provide several hours for the water to adjust)
3. Once you’re assured that the water is the same temp as the air, have one of your students place one of his/her hands (wet hand) in the bowl of water while keeping the other hand (dry hand) out of the water near the bowl, without touching the table, bowl or anything else.
4. Ask the student which feels cooler – the wet hand or the dry hand? Remind the student that they’re both the exact same temperature. Why would one hand feel cooler than the other if they’re the same temp?
Heat conduction is the answer. Water conducts heat from the wet hand much more quickly than air does from the dry hand and the student feels a marked difference.
Now have the student try this.
1. With the wet hand in the water, allow a minute or two for their hand to adjust to the water temperature.
2. Have the student keep their hand in the water as they monitor how warm/cold it feels.
3. Now have the student move their hand around in the water by wiggling their fingers and moving the entire hand for just a bit.
4. Ask the student if the water felt any different (colder or warmer). The water should immediately feel cooler as they move their hand.
5. Again, why would the water feel any cooler?
When the student had his/her hand in the water, heat was drawn away from their hand and the water immediately surrounding their hand warmed up a bit. When the student moved their hand again, the warmer layer surrounding their hand was disturbed, moved away allowing cooler water to take the place of the warmer layer and come in contact with their skin. The reverse of this works in a steamroom. If one sits quietly in a steamroom for a while and then moves about, you’ll immediately feel warmer because you’ve moved a layer of “cooler” air away from your body allowing the warmer air to come in contact with your skin.
Divers know this phenomenon well as this is how a wet suit works. The wet suit that divers wear doesn’t seal the body from water but allows some water to enter. The water that is trapped between the divers body and the suit quickly robs heat from the diver but then remains to keep the diver reasonably warm. So, instead of the diver’s body constantly losing heat to the surrounding lake or ocean, it has a thin layer of body-warmed water next to their body that takes little heat to maintain.
Key Concepts
Structures and Functions, Scientific Method/Approach
Questions
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