A soft, low-pitched, flat, tonal rumble of medium duration (~2.5-4 seconds) elicited by external events and associated with Attentive and/or Vigilant behavior. One or several elephants may call and such calling may or may not include overlapping vocalizations. External events that elicit such calling may include non-elephant disturbances such as unusual or loud commotion in a vehicle, a helicopter passing overhead, the discovery of Maasai herdsmen or other threat in the area, or the roaring of lions.
Elephants may also give similar calling in situations that are new, rather than frightening, such as the arrival of a known research vehicle. A disturbing, or exciting event among con-specifics (such as a fight between two musth males, or serious aggression directed at a family member) may also elicit this form of soft rumbling, as will playbacks of unexpected callers. We have referred to this form of rumbling as Comment-Rumbling, so-called because elephants appear to use it as a kind of "heads-up" to call attention to or "comment on" an unusual or disturbing event. It is quite possible that the rumbles in these various contexts are subtly different.
References: Poole 2011. (Full reference list)
This behavior occurs in the following context(s): Vigilance