Quantitative documentation of bear (Ursidae) mating behavior is sparse and incomplete. Understanding subtleties of mating behavior and how it differs between successful and unsuccessful mate pairings is a crucial first step to permit empirical testing of sexual selection hypotheses and to inform captive breeding efforts. Because bears possess extremely sensitive olfactory systems and are well known for marking behaviors, it is probable that they are able to sense reproductive status of conspecifics using chemosensory cues. However, very little is currently known of these phenomena in most bear species, including American black bears (Ursus americanus). Our study documents the entire consummatory phase of mating behavior and provides behavioral evidence of chemosensory communication of estrus status in American black bears. Using quantitative ethological methods, we discovered that successful mounts (with ejaculation) averaged 29-fold longer duration than unsuccessful mounts, with no overlap. Males were selective as to which specific estrus (of polyestrous females) and what day within a peak estrus they successfully mounted, and most investigated the females' anogenital region before mounting. Also, females housed together had synchronized estruses. We suggest it is feasible to estimate whether the mating activity of free-ranging bears is successful using only partial observation of the event (first 20 min). Moreover, our study supports the conclusion that chemosensory communication is used by black bears to identify conspecific estrus status. These data advance our basic understanding of bear mating behavior, are applicable to bear wildlife management and conservation efforts, and lay the foundation for further study of the ecology and evolution of sexual selection in bears.