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!)

http://www.iowadnr.gov/Education/ForTeachers/ClassroomResources.aspx

National Geographic Animals: Beaver

http://animals.nationalgeographic.com/animals/mammals/beaver/

NatureWorks: Beaver

http://www.nhptv.org/natureworks/beaver.htm

IDNR: Trapping & Fur Harvesting

http://www.iowadnr.gov/Hunting/TrappingFurHarvesting.aspx

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.