An often barely audible, flat or descending humming or pulsating sounding Rumble (‘mm-mm-mm’), of medium duration (~2-3.5 seconds) produced in a series by infants, calves and juveniles of either sex when they are separated from and searching for their mothers and/or families. The body posture of a lost calf (Chin-Out; Ear-Spreading, Tail-Raising; Trunk-Curved-Under) indicates that it feels insecure and frightened. The calf calls and then Freezes, standing with his head raised and ears spread, and Listens, presumably for an answer to his call, and then calls again. This pattern is repeated over and over, with the Rumbling sometimes increasing in amplitude, until he locates his mother or other family member. A separated calf's typically rapid movement, as it searches for his family, is likely to be the cause of the pulsating quality of the call.
Calves and juveniles have been playing in the water along with older males. Suddenly they realize that their mothers are calling and they are about to be left behind by their families. They begin to move from the water, some of them giving 'lost calls' or Separated-Rumbles and others Trumpeting as they run to catch up, still playing. This half playful behavior is typical of calves who are left behind, but not fearful of being truly lost or separated. (Amboseli, Kenya)
