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Matrilinear hierarchy in the American black bear (Ursus americanus).

ABSTRACT: The American black bear (Ursus americanus) was long thought to be solitary and its social organization has not been well described. Here, we present new data on black bear social structure. The objectives of the study were to make detailed observations of the behavior of wild black bears to determine their social interactions and structure. We tested whether black bears interacted socially beyond mating and competing for resources, if black bears tracked relationships and interacted regularly even when resources were not limited, and whether the social structure of a population of black bears was based on a matrilinear hierarchy. We collected data by direct observation of bears from 1993 to 2014. Observations of 1210 social interactions at a provisioning site indicated that females compete and form matrilinear hierarchies. Dominant bears established a hierarchy for food, control of space, and control of younger bears. Post interaction scent marking took place, which suggested that dominant females were conditioning subordinates to their scent marks. Affiliative behavior occurred between related and unrelated bears and helped to establish the social structure of the bear community. Based on our data, human-bear conflicts can be reduced by behavioral modifications by humans when they encounter bears. Knowledge of bear behavior and the matrilinear hierarchy provide a basis for non-lethal management of bears that find themselves in a bear-human conflict situation.

SUBMITTER: Kilham B

PROVIDER: S-EPMC9291961 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:American black bears (Ursus americanus) are seasonally polyoestrous and exhibit delayed implantation, which may allow equal and independent fertility of recurrent oestruses of a mating season. We postulated that the luteal inactivity during delayed implantation allows bears to have sequential ovulation during a polyoestrous mating season such that each oestrus of a polyoestrous female will have equivalent fertility, and pregnancy would not preclude subsequent ovulation and superfetation. Controlled mating experiments were conducted on semi-free-ranging female American black bears during three mating seasons, wherein females were bred by different male cohorts in each oestrus. Behavioural observation, vulva score ranking, genetic paternity analysis, gross morphology of ovaries and microscopic morphology of diapaused embryos were used to evaluate the fertility of each subsequent oestrus in polyoestrous females. Oestrus duration, number of successful mounts and median vulva scores were similar between first and subsequent oestruses of the season. Polyoestrus occurred in 81.3% of oestrous females, with a 9.7?±?5.5 day (mean?±?SD) inter-oestrous interval. Sequential ovulation was documented in three polyoestrous females, including one that possessed both a corpus haemorrhagicum and a developed corpus luteum. Among polyoestrous dams, four of nine embryos were conceived in the first oestrus and five of nine in the second oestrus. These results indicate that each oestrus of polyoestrous females is capable of fertility, even if the female is already pregnant from a prior oestrus. Although superfetation was not directly observed in the present study, our results strongly suggest the potential of superfetation in the American black bear and provide novel insight into the complex behavioural and physiological breeding mechanisms of bears. Given that most endangered bear species share similar reproductive traits with American black bears, captive breeding programmes could take advantage of superfetation by mating females with different males at each subsequent oestrus of the season in order to increase the genetic diversity of captive endangered bears.

Dataset Information

Matrilinear hierarchy in the American black bear (Ursus americanus).

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