Bison mother-offspring acoustic communication.

Mother-offspring communication is especially crucial for social species in order to synchronize activities essential for early survival including nursing, resting, maintaining proximity during group movements between food or water sources, and locating one another if separated in a large social group. One of the most social ungulate species in North America is the American Bison (Bison bison), formerly known as buffalo. Adult female bison associate with their young for over a year and communication between mother and offspring is likely essential for establishing and maintaining a bond upon which the life of a calf depends. One goal of this study was to quantify and compare the acoustic form of vocalizations of adult female, subadult, and calf bison and to determine how age classes differed in call structure. The other goal was to identify the contexts in which bison vocalized. Vocalizations of 101 bison (53 adult females, 15 subadults, 33 calves) in a semi-free-ranging herd in Montana were analyzed and found to be pulsatile sounds, unlike vocalizations of bison bulls or domestic cows and calves. Vocalizations of bison cows, subadults, and calves differed significantly in total duration, numbers of pulses, pulse duration, and pulse rate. Seven distinct call contexts were identified. The majority of calls were "moving-on calls" (39%), when a cow called and her calf ran to her side and the 2 moved on together, and "contact calls" (21%) when a cow called and her calf called back but neither changed their location. "Imprinting calls" and "nursing calls" were also identified. Mother-offspring acoustic communication in bison appears especially critical for coordinating movements. Understanding the role of acoustic communication in maintaining the bond between bison mothers and their offspring can contribute to the humane management and welfare of this iconic species.