North American beaver
The North American beaver (Castor canadensis) is one of the two living species of beaver, the other being the Eurasian beaver (C. fiber).[1] It is the second-largest living rodent after the capybara.[1]
Classification
Beavers form the family Castoridae. They are more closely related to squirrels and marmots than to mice.[1] The North American beaver has 40 chromosomes, while the Eurasian beaver has 48.[1]
Description
Adults usually weigh about 18 to 23 kg, although animals of about 44 and 50 kg have been recorded. Including the tail, the body is about 1.2 m long.[2] The broad tail serves as a rudder, a prop when felling trees, a signal when slapped on the water, a fat store and a way of losing heat. Valves close the nostrils and ears under water, and the lips close behind the incisors so that the beaver can gnaw while submerged.[2]
Distribution
The species ranges across North America, from Alaska, Hudson Bay and northern Labrador south to the Mexican border and Florida.[1] By 1900 it had nearly disappeared from the north-eastern United States. Heavy trapping had made it scarce in much of its original range by about 1900, and it has since been reintroduced to many areas.[3] In the Adirondacks about 15 were left around 1900, but after protection and releases between 1901 and 1906 there were about 15,000 by 1915.[4]
Family life
Beavers live in families that hold a territory around their pond.[5][6] They are socially monogamous, with both parents caring for the young, although it is not yet certain that they are genetically monogamous.[5][6] A family usually contains up to three age groups: the parents, the kits of the year and the yearlings. Müller-Schwarze gives about six animals as typical.[5][7] Young usually disperse at about two years old[3], and some older offspring stay on and help in the family.[5][8]
Beavers mark their territories with scent mounds of mud from the pond, scented with castoreum or with secretions from the anal glands.[9][10] Most mounds are built in spring, when young animals are dispersing.[9]
Building and feeding
Unlike the Eurasian beaver, which mostly lives in burrows or lodges in the bank, the North American beaver builds free-standing lodges and cuts almost any kind of tree.[1] Its dams keep lodge entrances under water, and they make it easier to move food and logs and to store food. They range from about 20 cm to 3 m high, and the longest known is about 850 m long. The sound of running water prompts beavers to build and repair them.[11] Aspen is the preferred food, and willow is the main food where aspen is scarce. In summer beavers eat mainly grasses, herbs and water plants.[12] Microbes in the caecum help them digest cellulose.[3]
Effects on landscapes
By damming streams, beavers raise the water table, store water, reduce erosion and trap sediment.[13] The ponds, swamps and meadows they create support more species.[14] The Smithsonian's National Zoo describes beavers as one of the few animals that greatly change their environment, providing habitat for dozens of other species.[13]
Fur trade
The North American fur trade ran from the mid-1600s to the late 1850s. Demand came mainly from Europe, where the fur was used to make felt hats.[15] The trade drew trappers across the continent to the Pacific and shaped European settlement.[15]
Status
Animal Diversity Web lists the North American beaver as Least Concern on the IUCN Red List.[3]
See also
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Müller-Schwarze, Dietland (2011). The Beaver: Its Life and Impact (2nd ed.). Comstock Publishing Associates. ch. 1. ISBN 9780801461347.
- ↑ 2.0 2.1 Müller-Schwarze, Dietland (2011). The Beaver: Its Life and Impact (2nd ed.). Comstock Publishing Associates. ch. 2. ISBN 9780801461347.
- ↑ 3.0 3.1 3.2 3.3 Anderson, R. (2002). "Castor canadensis". Animal Diversity Web. University of Michigan.
- ↑ Müller-Schwarze, Dietland (2011). The Beaver: Its Life and Impact (2nd ed.). Comstock Publishing Associates. ch. 18. ISBN 9780801461347.
- ↑ 5.0 5.1 5.2 5.3 Müller-Schwarze, Dietland (2011). The Beaver: Its Life and Impact (2nd ed.). Comstock Publishing Associates. ch. 5. ISBN 9780801461347.
- ↑ 6.0 6.1 Busher, Peter (2007). "Social Organization and Monogamy in the Beaver". In Wolff, Jerry O.; Sherman, Paul W. (eds.). Rodent Societies: An Ecological and Evolutionary Perspective. University of Chicago Press. p. 281. ISBN 9780226905365.
- ↑ Busher, Peter (2007). "Social Organization and Monogamy in the Beaver". In Wolff, Jerry O.; Sherman, Paul W. (eds.). Rodent Societies: An Ecological and Evolutionary Perspective. University of Chicago Press. p. 283. ISBN 9780226905365.
- ↑ Busher, Peter (2007). "Social Organization and Monogamy in the Beaver". In Wolff, Jerry O.; Sherman, Paul W. (eds.). Rodent Societies: An Ecological and Evolutionary Perspective. University of Chicago Press. p. 282. ISBN 9780226905365.
- ↑ 9.0 9.1 Müller-Schwarze, Dietland (2011). The Beaver: Its Life and Impact (2nd ed.). Comstock Publishing Associates. ch. 6. ISBN 9780801461347.
- ↑ Busher, Peter (2007). "Social Organization and Monogamy in the Beaver". In Wolff, Jerry O.; Sherman, Paul W. (eds.). Rodent Societies: An Ecological and Evolutionary Perspective. University of Chicago Press. p. 285. ISBN 9780226905365.
- ↑ Müller-Schwarze, Dietland (2011). The Beaver: Its Life and Impact (2nd ed.). Comstock Publishing Associates. ch. 7. ISBN 9780801461347.
- ↑ Müller-Schwarze, Dietland (2011). The Beaver: Its Life and Impact (2nd ed.). Comstock Publishing Associates. ch. 9. ISBN 9780801461347.
- ↑ 13.0 13.1 "Beaver". Smithsonian's National Zoo and Conservation Biology Institute.
- ↑ Müller-Schwarze, Dietland (2011). The Beaver: Its Life and Impact (2nd ed.). Comstock Publishing Associates. ch. 16. ISBN 9780801461347.
- ↑ 15.0 15.1 Müller-Schwarze, Dietland (2011). The Beaver: Its Life and Impact (2nd ed.). Comstock Publishing Associates. ch. 17. ISBN 9780801461347.