Manual of beaver management within the ... - DANUBEPARKS

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Manual of beaver management within the Danube river basin4. ENGINEERING ACTIVITIES4.1. Gnawing of treesClearest signs of beaver presence in a locality are the trunks of trees characteristicallygnawed to hourglass shape. Beavers gnaw trees to:- bring food closer- obtain building materials for construction and repair of weirs, lodges, burrows anddams.Beaver uses very sophisticated security system for felling. When felling trees, no injuryhappens (or almost never happens) to any family member. On principle, beaver gnawsthick trunks circumferentially, so that he does not shift the focus. It allows it to retain theslimmest ungnawed core, and the felling of trees is not limited by their size. Beaverleaves the core part of trunk ungnawed and lets the stronger winds to topple down thetree. Besides this, it responds quickly to each crackle (sound) by fleeing into hiding.Beaver is unable to perform directed felling. Direction of treefall is determined by thefocus of the crown. Logically it's the side with greater intensity of solar radiation, i.e.from the outer edge of the forest stand.4.2. Building activityBeavers' need for security and safety of each family member is extremely strong andunusual in comparison to other animals. They spend much time and energy thereby.They engage the whole family by particularly extensive building activity to securethemselves. Range of beaver structures include:- burrows and burrow systems,- weirs and weir systems,- reservoirs and reservoir systems,- lodges,- channels,- dams and dam systems.The aim of the building effort is to slow down the flow, increase water levels andincrease the water surface. This ensures concealment of the entrances to the burrows,possibilities of escape in case of the attack, facilitated transport of building materialsand food supplies, and, not least, changes habitat conditions to accommodate moreplants preferred by beaver.4.2.1. Digging activity4.2.1.1. Resting hauntPlace to beaver daily stay in summer. It is located in close proximity of water, sothat in case of danger the animal can escape to water in few jumps. Beavers buildthem mostly in a tangle of roots of alder or willow trees growing on the flooded lowbanks. For this purpose, they dig a depression at the foot of the tree, remove tangledroots, and strew it with bark chips and gnawed twigs13
Manual of beaver management within the Danube river basin4.2.1.2. Burrows and burrow systemsMost common type of dwelling. In cases where the banks of streams or dams are highenough, beavers dig burrows. They are often very complicated and multi-level with lotsof corridors leading into the water (usually 3 to 5) and blind corridors with nest(chambers). The length of corridors may reach several tens of meters. Burrows arewide and high of more than 25 cm. Beavers dig burrows just below the surface. Oftenburrows slump by weight of man or larger animal. Entrances are under water, ventscan be found on the banks. Only if the water freezes, beavers create entrance on drysoil. Because burrows often collapse, beavers repair holes by putting branches and soilinto the ceiling hole. Later, they add material from the outside and build something inbetweenthe burrow and the lodge.Fig. No. 1.: Beaver burrow4.2.1.3. ChannelsTo increase the safety standard of the family, beavers dig up channels.On the banks, they dig long narrow flooded walkways - a corridor that will provide saferaccess to distant sites. Beaver deepens the channel by digging in soil, and gnawing inpeat and reed. Shallow sections with insufficient depth are inclosed. Beaver channelscharacteristically converge to the lodge. Channels are built mostly in the second half ofthe summer at lower water levels.Beavers can completely change the appearance of inhabited shores by their diggingactivity.It is not rare that beavers adapt to the offer of the locality and, for example, occupy avariety of technical works. A particular example is the settlement of beavers in a stormsewer of urbanized district of the city. They accommodate this unusual undergroundsystem to their needs by building a small weir, which serves as a feeding stool at asame time.14
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