Namibian elephants emit low-frequency calls at precise times of the day when atmospheric conditions are most favorable for sound propagation.
Professor Michael Garstang from the University of Virginia in the United States reported that during a three-week study using a meteorological setup and eight microphones, the team found that 42% of the elephants’ calls occurred during the calm air period—three hours after sunset.
The second most frequent calling time was about two hours after sunrise, which also coincides with the best acoustic conditions for transmitting sound over long distances. Among the 1,300 calls recorded in the study, 94% fell within these two time frames.
Calm air refers to a layer of cold air close to the ground, separated from the warmer air above by a stratification layer, similar to the temperature inversion phenomenon often seen in valley cities (where a layer of cold fog lingers near the ground and is prevented from rising due to the warmer air above). When sound waves are emitted into the atmosphere and encounter this stratification, they are bent back down to the ground, allowing them to travel further.
This calm air phenomenon—common in polar regions—can transmit human sound at audible frequencies up to 3 kilometers.
However, in Namibia, the sun heats the ground daily, causing temperatures to rise and disrupting these stratifications, leading to less optimal conditions for long-distance communication. To test this hypothesis, Garstang’s team set up an atmospheric measurement device and released weather balloons to record wind speed and temperature at various altitudes in the area.
Elephants need to communicate over long distances to mate. Female elephants have a short breeding window and must find the best males. The only way to achieve this is by producing alluring calls and listening for responses. This indicates that elephants are aware that dawn and dusk are the best times for communication.
M.T. (according to ABC Online)