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Pair formation, duration of pair-bonds, and mate replacement in a population of beavers (Castor canadensis)

Svendsen, Gerald E.
Canadian journal of zoology 1989 v.67 no.2 pp. 336-340
Castor canadensis, breeding, death, females, lakes, males, monogamy, streams
Characteristics of the breeding units in a population of North American beavers (Castor canadensis) are presented. All breeding units were monogamous. The hypothesis that a successful pair-bond usually occurs between an older and larger female and a younger and smaller male was rejected. Fifty-six percent of all pairs were formed in the months of September, October, and November. Newly formed pairs occurred predominantly between a resident beaver that had not yet acquired a mate, or had lost a previous mate, and an immigrant. A 2-year-old size beaver was one of the pair mates in 90% of newly formed pairs. The average pair-bond lasted 2.5 years. The length of a pair-bond was associated with conditions at the site of residency; beavers living in the more stable conditions (lake sites) remained together longer than did beavers living in comparatively unstable conditions (stream sites). Loss of the male was the cause of 39% of the breakups of pairs, loss of the female, 61%. Desertion was documented in 4%. Because of the age discrepancy at the time of pairing, death of one of the mates was presumably the major cause of mate turnover.