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.
We refer to calls of this quality, given in this context as Separated-Rumbles or Lost-Calls. As the calf becomes more distressed, Separated-Rumbles may develop into Rumble-Roar-Rumbles.
References: Poole 2011. (Full reference list)
This behavior occurs in the following context(s): Calf Reassurance & Protection, Protest & Distress