Iowa Mammals
Mammals are warm-blooded, have a
back-bone, are hairy, and have mammary glands that produce milk to feed their
young. Mammals live on all continents and in all oceans. Iowa has 40 species of mammals that are
considered common in the state. Iowa’s mammals live in woodlands, prairies,
waterways, farm fields, and towns. They are adapted to a wide variety of
habitats.
Creature Feature – Beaver (Castor Canadensis)
Beaver are
common in Iowa and are found throughout the state. Beaver may grow up to 4 feet
long, including their 9-18 inch tail, and weight up to 60 pounds. They are
North America’s largest rodent.
Beaver
live in streams, ponds, lakes, and wetlands. They are superbly adapted for the
aquatic habitats; they have waterproof fur and a thick layer of underfur,
webbed back feet, nose and ear valves that close while swimming, a special
membrane to protect their eyes under water, they can hold their breath for up
to 15 minutes, and they are able to raise the back of their tongue to close the
passage to their lungs so water does not enter their lungs when they open their
mouth under water (such as when they are gnawing branches under water).
Beaver eat
the inner bark, twigs, and leaves of trees and shrubs. They also eat aquatic
plants such as duckweed, grasses, and water lilies. Beaver have colonies of
microorganisms in their intestines that digest up to 30% of the cellulose from
trees bark and other woody material they eat. During the winter months their
diet consists mainly of woody material, such as twigs and branches, they have
stored near the entrance to their lodge. Beaver do not hibernate and remain
active all year. Beaver are nocturnal and are most active at night.
Beaver
modify their environment for their own purpose more than any other animal except
humans. They dam streams and creeks to creating wetlands and ponds. Their dams
consist of sticks, branches, and mud dredged up from the bottom of the pond or
stream. They dig burrows into the bank or construct dome-shaped lodges of small
trees, limbs, sticks and mud. The
entrances are placed below the water level but the living area inside is above
the water level.
Beaver are highly social animals and live in family groups consisting of
the parents (beavers mate for life), young of the year and two-year old
offspring. The average litter size is 3, so a beaver lodge with a family of 8
beaver is not uncommon. Beavers will mark their territory with scent mounds
made of mud, feces, and castoreum, an aromatic secretion produced by their
castor gland.
Links
IDNR: Education – Classroom
Resources (go to the Document Library at the bottom of the page for fact sheets
and activity sheets!)
National Geographic Animals: Beaver
NatureWorks: Beaver
IDNR: Trapping & Fur Harvesting
Book List
Gibbons, G. 2012. Beavers. Holiday
House, Inc.
Holland, M. 2014. The Beavers’
Busy Year. Sylvan Dell Publishing.
Muller-Schwarze, D., L. Sun. 2003. The
Beaver: Natural History of a Wetlands Engineer. Cornell University Press.
Swanson, D. 2010. Beavers.
Whitecap Books, Limited.
