7.9. SR 12-16-1996 - Laserfiche WebLink

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B-4 lodges and bank dens, depending on the situation. All lodges and bank dens have at least two en- trances and may have four or more. The ledge or bank den is used primarily for raising young, sleep- ing and some food storage during severe weather (Figure 5). The length or height of a dam generally depends upon what is necessary to essentially stop the flow of water and create a pond. In areas of flat topography, the dam, re, ay, not be~,.ov~,~. 3~, i. nches,.(.9~,. m) high, but as much as 1/4 mile (.4 km) long. In hilly or mountain country, the dam may be q0 feet (3 m) high and only 50 feet (15 m) long. The size of the tree the beaver cuts is highly variable, from a 1-inch (2.54 cm) DBH (diameter at breast height) softwood to a six- foot (1.8 m) DBH hardwood. In some areas beavers seem to cut down trees up to about 10 inches (25 cm) DBH and merely girdle or partially cut larger ones, although they often cut down much larger trees. For some reason the bea~ers seem to like to girdle large pines and sweetgums. They like the gum or storax that seeps out of the girdled area of sweetgum and other species. An important factor about beaver biology is thei~ territoriality. A col- ony generally consists of four to eight related beavers, who resist additions or outsiders to the col- ony or the pond. Young beavers commonly are displaced from the colony shortly after they become sexually mature, at about 2 years old. They often move to another area to begin a new pond and col- ony. However, some become solitary hermits inhabiting old abandoned ponds or a farm pond if one is available. Beavers have a few natural predators aside from man, in- cluding coyote, bobcat, river otter and mink on young kittens. In other areas, bear, wolves, and wolverines may prey on beavers. They are hosts for several ectopar- Figure 6. Pine plantation in Arkansas killed by floodin8 caused by beavers. asites and internal parasites in- cluding nematodes, trematodes and coccidians. Giardia lamblia is a pathogenic intestinal parasite transmitted by beavers, which has caused human health problems in water supply systems. In fact, the Centers for Disease Control have reports of at least 41 waterborne Giardiasis outbreaks affecting more than 15,000 people. For more infor- mation about Giardiasis, see von Oettingen (1982). 'This thesis con- tains a number of additional references. They generally are monogamous; copulation may take place either in 'the. water or in the lodge or bank den. They communicate by vocalizations, posture, tail slapping and scent posts or mud dobs or mounds placed around the bank and dam. The beaver's castor glands secrete a substance that is deposited on mud dobs to mark territorial boundaries. These scent posts are found more frequently at certain seasOns, but.are found year-round in active ponds. The habitat modification by beavers, caused primarily by dam building, is Often beneficial to fish, furbearers, reptiles and amphibians and to waterfowl and shorebirds. However, when this modification comes in conflict with man's objec- tives, the impacts of damage may far outweigh the benefits. Damage and Damage Identification Most of the damage caused by beavers is a result of dam building, bank burrowing, tree cutting or flooding. Some individual south- eastern states where beaver~dam- age is extensive have determined from surveys that beaver damage estimates range from $3 million to $5 million dollars annually to timber loss, crop losses, roads, dwel in&~,, a.nd property flooded, 'and other damage. In some of these states, bottomland hardwood timber in areas of several thousand acres in one watershed maybe lost because of beaVer pond flooding. Some unusual cases observed over the years include state highways flooded because of beaver ponds, reservoir dams destroyed by bank den burrows collapsing, and train derailments caused by burrowing. Housing developments have been threatened by beaver dam flood- ing, and thousands of acres of croplands and young pine planta-