Beaver Management in Anchorage David Saalfeld Regional Wildlife Biologist Alaska Department of Fish and Game
General Biology • Largest rodent in North America • Continue to grow in body size throughout their lives • Average 40-70 lbs, but have been known to grow to 100 lbs • Primarily nocturnal, but sometimes active during day
North American Range
Reproduction • Monogamous — mated pair will live together for many years, sometimes for life • Breeding season in January/February • Gestation 107-110 days • 2-4 kits born April-June • Kits eyes are open at birth, and they are covered with soft fur • Nurse for 2-3 months • Can swim at 4 days
Longevity • When foraging away from water, vulnerable to wolves, coyotes, bears, lynx • Other causes of mortality include winter starvation, disease…and falling trees • Generally live 5-10 years in wild
Colonies • Beavers live in family units: Mom, Dad, and the kits • Kits stay with parents until 2 years old • Most beavers will reproduce at 3 years of age • Beavers are very territorial, and will defend their area from any other beavers
Designed for Underwater Operations • Nictitating membranes protect eyes • Nose and ear valves close • Draws lips tightly behind teeth when carrying wood • Can hold breath for 10-15 minutes
Coat • Short, fine hairs for warmth • Longer hairs for waterproofing • Beavers frequently groom their fur and waterproof it with castor
Castoreum • Found in “glands” near the base of the tail • Both male and females have castor sacs • Used for marking territory • Protect and waterproof fur • Human uses for castor include lure for trapping beavers, perfume, food additive, and historically it was used in some medicines
Tail • Used as a rudder • Slaps as a warning • Used for balance when standing on hind legs
Feet • Webbed hind feet for swimming • Front paws skillful at manipulating objects
Teeth • Never stop growing • Self-sharpening — the inner surface is softer than the outer enamel, so wears away faster to create a sharp edge
Diet • Vegetarians • Fresh leaves, stems, twigs, bark, aquatic plants, roots, grasses • Preferred tree species include alder, aspen, birch, cottonwood, poplar and willow • If preferred species unavailable, will eat most woody plants • Often travel >100 yds from water • Food for winter use stored in underwater caches
Structures • Dams • Lodges • Bank Dens
Dams • Flood areas for protection from predators, access to food supply, and to provide underwater entrances to dens. • Beavers living on water bodies that maintain a constant level (e.g., lakes, large rivers) do not build dams.
Dams • Dams are constructed and maintained with whatever materials are available — wood, stones, mud, and plant parts. They vary in size from a small accumulation of woody material to structures 10 ft high and over 165 ft wide • The average tree used in construction of a dam is 4- 12” at the stump…but use of trees 150’ tall and 5’ across have been recorded
Lodges and Bank Dens • The beaver’s home • Both have one chamber and at least one exit to deep water • Freestanding lodges usually built in lakes/ponds, or areas where the bank or water levels aren’t sufficient for a safe bank den • Bank dens are often in large, swift streams • Lodges consist of mound of branches and logs, plastered with mud • One or more underwater openings lead to tunnels that meet at the center of the mound • Bank dens are dug into the banks of streams and large ponds, and beavers may or may not build a lodge over them • Bank dens may also be located under stumps, logs, or docks
Lodges
The Challenges of Beaver Management • Anywhere there are beavers, we two opposing viewpoints among local residents • Benefit/Cost
Environmental Benefits • Water quality • Creation of habitat for other species • Creation of open space • Reduction of erosion
Water Quality • Beaver ponds help remove sediment and pollutants from waterways, including suspended solids, total nitrogen, phosphates, carbon, and silicates
Creation of Habitat • As trees are drowned by rising water, they become ideal for woodpeckers — whose cavities in turn draw other cavity nesting birds • Canada Geese and Trumpeter Swans have been known to depend on beaver lodges for nest sites
Creation of Habitat • Beaver ponds have been shown to have a beneficial effect on trout and salmon populations • Beaver ponds may be especially important wintering habitat for salmonids • Beaver dams develop new wetlands, benefitting a variety of other species, including waterfowl, bears, moose, gulls, etc. • Removal of some pond-side trees increases the grass/forb/shrub layer, creating more waterfowl nesting habitat adjacent to water
Creation of Open Space • When beaver ponds eventually silt in, fertile “beaver meadows” are gradually formed, creating open space that benefits a variety of other species
Reduction of Erosion • Beaver dams deepen and reduce flow, decreasing bank erosion
Beaver/Human Conflicts • Flooding • Issues with water facilities such as stormwater systems • Damage to forests and landscaping • Undermine roads • Dams can sometimes be an impediment to fish — but not as often as commonly thought • University Lake — aggressive beavers
“Beaver Fever” • Debilitating (to humans) gastrointestinal distress caused by the parasite Giardia lamblia • You get it from drinking water containing the parasite • Beavers are not the only animals that carry it
Anchorage
SHIP CREEK Glenn Pond below Alderwood Park 5th K FISH CREEK E a E L r R g C n Eastchester Lagoon D S Fork Chester Cr I O University Lake International Airport T u d o r Elmore Reflection Lake k e e r C l l e b p L R a s p b e r r y m i t t l e a C C a m p b e l l C r e e k Taku Lake Seward CAMPBELL LAKE CRAIG CREEK O ' M a l l e y Hillside FURROW CREEK RABBIT CREEK E K E C R T B I A B R E T L T L I Little Survival Creek POTTER CREEK
Management Options • Education • Exclusion • Dam Removal • Water Flow Devices • Trapping/Removal • Combination
Education • Speak to community groups • Educate personnel from other agencies; work with Municipality to draft policies guiding beaver management in Anchorage • Educate landowners: often used when there is not a real problem — beavers are simply present
Exclusion • Sturdy fencing is the primary means of exclusion. • Individual trees are best wrapped with hardware cloth forming a cylinder standing at least six inches away from the trunk. • Property is best fenced with welded wire fencing.
Dam Removal (hand removal) • Used in certain situations, if volunteers are willing to put forth effort
Water Flow Devices (Flooding Prevention) • Pond Levelers (Beaver Dam Pipes) • Culvert Protectors • Combinations
Pond Levelers • Beavers plug leaks in their dams quickly to maintain water levels • The sound of running water stimulates them to plug holes • Pond Levelers eliminate the sound and feel of flowing water
Pond Levelers
Culvert Protectors • Beavers often plug culvert pipes under roads, resulting in flooding • To be effective, a culvert fence needs to be wide, forcing the beavers to dam a long section of fence
Water Flow Devices • Appropriate for certain situations, but not all • Generally most successful if the water level does not have to be dropped very far • Must be installed correctly and maintained • If some degree of elevated water is acceptable, water flow devices should be considered • Sometimes trapping is necessary before installation
Common Reasons for Failure of Water Flow Devices • Beavers construct a new dam • Improper design (e.g., insufficient pipe capacity) • Lack of maintenance • Beavers dam the fencing • Vandalism
Relocation • Very rarely an option • Most habitat suitable for beavers…already has beavers • Beavers are territorial, so newcomers will likely be chased away
Trapping/Removal • Last resort — but is often the most practical solution • If trapping or shooting is to be done to remove beavers in the event of conflicts with humans, it is ONLY to be done under a permit issued by ADF&G • Any beavers removed by lethal means become the property of the state and hides/skulls are used for educational purposes • Not a long term solution
Evaluation of a Conflict • Can beavers and humans coexist in this area? • Are nonlethal means likely to be successful? • Is the landowner interested in trying nonlethal means…at their own expense? • Is there likely to be damage to a structure or other property? • What is the landowner willing to do to prevent future problems?
If you become aware of a conflict between humans and beavers • Do not take action on your own • ADF&G needs to evaluate the situation to decide upon the appropriate management response • Call ADF&G at 267-2344
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