Mating System

Beaver pairs mate for life; therefore beavers are considered a monogamous species ("Beaver: Canadian Domain," 2004; Sun and Mueller-Schwarze, 2003). Although they are monogamous, a beaver will take another mate if the first dies ("Beaver: Canadian Domain," 2004). In addition, as with most monogamous species, extra pair copulations are possible (Sun and Mueller-Schwarze, 2003).

Beavers are obligate monogamous species, meaning both parents are needed to raise offspring. Single adult beavers have been observed but all lone beavers are solitary only temporarily (Sun and Mueller-Schwarze, 2003). There are several reasons why beavers have evolved to be obligate monogamous. First of all, beavers need a division of labor between the two parents in order to raise kits successfully, because one beaver cannot handle all of the work involved. Both males and females take part in scent marking, defending the territory, and repairing of dams and lodges (Sun and Mueller-Schwarze, 2003). When a litter is born the female is the primary caretaker of the kits, while the male continues to maintain the territory (Sun and Mueller-Schwarze, 2003).

Beaver Hard at Work

Image courtesy of Michael Leps from http://www.natur-lexikon.com/Texte/ml/001/00002/ml00002.html

Also after the kits are able to leave the den, which usually occurs at one month, there is still a relatively long period of offspring dependence (Sun and Mueller-Schwarze, 2003). This extended period of dependence increases the need for both parents. Offspring almost always stay with the parents for about a year, relying on them for food, shelter, and protection from predators (Sun and Mueller-Schwarze, 2003; Wheatley, II. Sex, Age, and Family Status, 1997). During this period of dependence, imprinting occurs and allows for important developments in the young beavers' life (Sun and Mueller-Schwarze, 2003). Offspring learn valuable skills by copying their parent’s behavior; however, they are still not yet effective helpers (Sun and Mueller-Schwarze, 2003). It would be difficult for one adult to provide for offspring for such a long period of dependence and maintain a territory at the same time. The beavers' territory is extremely important, especially with kits, because it contains lodges and dams that protect beavers from predators (Rosell and Czech, 2000). As mentioned in the section on predators, adult beavers have very few successful predators (Rosell and Czech, 2000). This is because of the extremely effective protection that the lodge and dam provide beavers (Rosell and Czech, 2000). Also, beavers put a lot of energy into territories, creating lodges, creating dams, leaving scent mounds, and becoming familiar with the area (“Beaver: Canadian Domain,” 2004; Rosell and Nolet, 1997). The beavers cannot afford to lose their large investment of energy, while they are taking care of young. Two beaver parents working together allow for the offspring to be raised and the the territory to be maintained.

Another contributing factor to beavers’ monogamy is a very short breeding season. The breading season is usually during the months of January and February; however, females are only in estrous for twelve hours at a time (Rosell and Bergan 2000). Because of such a small window of opportunity it is very important for males to know when females are in estrous so successful copulations can occur. Monogamy in beavers helps make this possible. Males and females stay in close proximity with contact occurring within the lodge daily (Rosell and Bergan 2000). However, beavers spend a good portion of the day out of the lodge as well; therefore, good communication between the male and female is necessary. A female can communicate to the male that she is estrous by excreting deposits on top of sent mounds soon after ovulation (Rosell and Bergan 2000). The male checks the mounds in the territory regularly, and so the deposits are able to attract a male to the female from a distance (Rosell and Bergan 2000).