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Social monogamy, considered rare in mammals, has been described in two species of beaver, the Eurasion beaver (Castor fiber), and the North American beaver (Castor Canadensis). Social monogamy, however, does not necessarily imply genetic monogamy. For example, in group living mammals, females may engage in extra-pair copulations as a result of increased female mate choice opportunities. Recently, following genetic analysis, a wide range of genetic relationships among colony members have been documented in the North American beaver, including extra-pair paternity. Here, we used microsatellite loci to provide parentage estimates from colonies of the Eurasian beaver in the Kirov region, Russia. No evidence for the presence of any extra-pair young was detected. However, in two cases, we found a pair of unrelated males inhabiting a single colony. Our results suggest that while colonies may comprise both related and unrelated individuals, the genetic mating system appears to match that of the previously inferred social monogamy.
The Eurasian beaver Castor fiber Linnaeus, 1758 deposit castor fluid (castoreum) and/or anal gland secretion at scent mounds in their territory year round. We investi­gated the hypothesis that during winter Eurasian beavers may intensify use of scent, in year round ice-free water systems, during the breeding season. This study showed that the median number of scent marks in 7 territories increased significant ly in the breeding (January-March 1996}, compared to the nonbreeding portion of winter (October- -Decemher 1995), which is consistent with our prediction. The median number of scent marks was significantly higher during February, compared to January and March. This may be due to females approaching or being in oestrous in our study area during February. Further studies are, however, needed to clarify how information in scent marks are coded and transmitted during the breeding season.
An abnormally long incisor of an adult Eurasian beaver Castor fiber Linnaeus, 1758 is reported. The animal weighed about 20 kg and was in good condition when shot at 3 years of age. The tooth had grown at an angle in towards the beaver's left eye. Assuming the animal to be 35 months old and total tooth length to be 13.5 cm, then growth rate would have been 0.39 cm per month. This report indicates that beaver can survive despite abnormal growth of one incisor.
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