Eat, Sleep, and Build

In Season 1, Episode 4 of The Life of Mammals, beavers (Castor Canadensis) not only breathe, sleep, and eat as other mammals, but they also build. Attenborough witnesses a North American beaver building a dam in this documentary. Castor Canadensis are a species that align mud, sticks, and stones to one side of the dam, while stacking logs and branches to blockade the other. When there is leakage in the dam, signaled by a trickling noise, these beavers immediately work to patch it.  They typically build dams on streams or small watercourses between ponds, but not on large rivers or lakes [4]. The result is high water levels in their habitat, where Castor Canadensis swim effortlessly and escape predation by holding their breaths for up to fifteen minutes underwater [3]. It is hypothesized that the watery site serves as a territorial force field against predators [2]. Another consequence of dam-building is the restoration of vegetation and plant diversity, which is why beavers are dubbed as “ecosystem engineers” [3].

But Castor Canadensis not only build dams. They also build lodges with secret underwater entrances and channels. Lodges serve as shelter during the winter months and as protection from predators. Additionally, lodges house the breeding grounds of a monogamous pair of beavers. Beaver parents raise their offspring in lodges, and both sexes are highly territorial of the surrounding area [1]. Researchers suggest that establishing territory is critical for a beaver’s individual fitness, or lifetime reproductive success [1]. By maintaining and defending their territory through dam and lodge-building, beavers increase their fitness—or survival rate and number of produced offspring. Therefore, it is not surprising that beaver families build and sustain dams and lodges for the rest of their lives —that is, until beaver young are old enough to leave their parent’s home, find a mate, and colonize a new territory [1].

(The Life of Mammals. Season 1, Episode 4, starting at approximately 17:49)

by Joyce Choe


  1. Mayer M, Zedrosser A, & F Rosell. 2017. Couch potatoes do better: Delayed dispersal and territory size affect the duration of territory occupancy in a monogamous mammal. Ecology and Evolution 7: 4347-4356.
  2. Salandre JA, Beil R, Loehr JA & J Sundell. 2017. Foraging decisions of North American beaver (Castor Canadensis) are shaped by energy constraints and predation risk. Mammal Research 62:229-239.
  3. Law A, Gaywood MJ, Jones KC, Ramsay P, NJ Willby. 2017. Using ecosystem engineers as tools in habitat restoration and rewilding: beaver and wetlands. Science of the Total Environment 605: 1021-1030.
  4. Zurowski W. 1992. Building activity of beavers. Acta Theriologica 37: 403-411.

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