Skip to main content

Why do beavers build dams? - Glynnis Hood

  • 164,377 Views
  • 719 Questions Answered
  • TEDEd Animation

Let’s Begin…

Nestled in the forests of Canada sits the world’s longest beaver dam. This 850-meter-long structure is large enough to be seen in satellite imagery and has dramatically transformed the region, creating a pond containing 70 million liters of water. But dams of any size can have huge impacts on their environment. So how exactly do beavers build these impressive structures? Glynnis Hood investigates.

Create and share a new lesson based on this one.

About TED-Ed Animations

TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »

Meet The Creators

  • Educator Glynnis Hood
  • Director Keegan Thornhill
  • Narrator Alexandra Panzer
  • Storyboard Artist Keegan Thornhill
  • Animator Keegan Thornhill
  • Background Artist Jonathan Martin Allan
  • Composer Salil Bhayani, cAMP Studio
  • Sound Designer Amanda P.H. Bennett, Chengqing Zhu, cAMP Studio
  • Director of Production Gerta Xhelo
  • Producer Anna Bechtol
  • Associate Producer Abdallah Ewis
  • Editorial Director Alex Rosenthal
  • Editorial Producer Dan Kwartler
  • Script Editor Renae Reints
Additional Resources for you to Explore
Originating in North America, the beaver family (Castoridae) dates back to approximately 37 million years before present, and then expanded its range to Europe and Asia around 33.5 million years ago. Despite having at least 30 different genera over their long evolutionary history, including the giant beaver (Castoroides ohioensis), now only two species of beavers remain – the Eurasian beaver (Castor fiber) and the North American beaver (Castor canadensis). Although they are genetically different and have some anatomical differences, both species of beavers are ecologically similar. In Eurasia and North America, beaver dams and lodges dot the landscape wherever there are beavers.

The ability of beavers to build structures, such as dams and lodges, flood large areas, and dig extensive networks of channels is typical of ecosystem engineers. By altering aquatic and riparian habitats in dramatic ways, beavers increase the types and diverse structure of habitats that then support other species. Along with changing the physical nature of habitats, flooding and foraging by beavers also change the dynamics among species in these ecosystems. As such, beavers are often called a keystone species. In a stone arch, if the keystone is removed, the entire arch collapses. Similarly, if a keystone species is removed from the ecosystem can collapse as well. The presence of beavers is often associated with an increase in aquatic macroinvertebrates, waterfowl, other semi-aquatic mammals (e.g., river otters and muskrats), and many other plants and animals.

As a long-lived monogamous species, beavers can change landscapes over long periods of time. Typically, a family group (“colony”) will have two adults, two to three juvenile beavers, and two to three young of year (“kits”). Generally, juvenile beavers do not disperse to find their own territories and mates until they are at least two years old. As a rule, the adults are monogamous and mate for life. Having multiple generations in one colony provides more workers for maintaining dams and lodges, and for collecting woody stems for their winter food caches, which are critical for accessing food when the ponds are covered in ice for months on end. Beavers do not hibernate and are still active under the ice throughout the winter, a time when they also mate and later give birth to their kits.

Their ability to change landscapes to suit their ecological needs can bring beavers into conflict with humans. The flooding that follows the building of dams or plugging of culverts can be especially irksome for humans. Often beaver dams and/or the beaver colony are removed, only to be reoccupied by more beavers that then build more dams. If the habitat is suitable, it is only a matter of time before a dispersing beaver will choose it for its new territory. One beaver cannot move into another beaver family’s territory without a fight, and it is often the dispersing beaver who loses and continues its search for a new home.

Fortunately, there are several ways that beavers and humans can coexist. To counter flooding, flow devices, also called pond levellers are used so the associated wetland stays intact, and the human facilities remain undamaged. These devices involve the placement of a piping system through the dam at the same height as the desired water level for the pond. When the water gets too high, it flows through the pipe, only to stop once the pond returns to the desired water level. Keeping beavers on the landscape not only increases access to critical habitats for many species, their activities increase groundwater recharge and the availability of surface water for humans as well. Beavers have made a tremendous comeback from near extinction, and with that comeback our ecosystems and water resources have benefited as well.

Customize this lesson

Create and share a new lesson based on this one.

About TED-Ed Animations

TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »

Meet The Creators

  • Educator Glynnis Hood
  • Director Keegan Thornhill
  • Narrator Alexandra Panzer
  • Storyboard Artist Keegan Thornhill
  • Animator Keegan Thornhill
  • Background Artist Jonathan Martin Allan
  • Composer Salil Bhayani, cAMP Studio
  • Sound Designer Amanda P.H. Bennett, Chengqing Zhu, cAMP Studio
  • Director of Production Gerta Xhelo
  • Producer Anna Bechtol
  • Associate Producer Abdallah Ewis
  • Editorial Director Alex Rosenthal
  • Editorial Producer Dan Kwartler
  • Script Editor Renae Reints

More from Awesome Nature