Sept. 14, 2005 — Namibian elephants really know the airwaves, say researchers who have discovered that the big mammals prefer to broadcast their very low-frequency calls at exactly the times of day when the air is best for carrying sound a long way.

In a three-week study that incorporated a range of meteorological equipment and an array of eight microphones, 42 percent of all elephant calls were made during the stable air period three hours after sunset.

The next most popular calling time during the two hours after sunrise, also a time when the acoustics of the atmosphere are the best for carrying calls great distances.

"This project was an attempt to demonstrate in the field predictions we had made with mathematical, acoustical models," said Michael Garstang of the University of Virginia.

A paper co-authored by Garstang, reporting the results of the work, appears in the current issue of the journal Earth Interactions.

Of about 1,300 calls recorded during the study, most fell within those two time periods, he said.

Garstang's interest extends to other animal calls as well, he said, but elephants were the logical animal to study, since they produce the loudest calls that, because they are made at infrasound frequencies, should theoretically reach the furthest.

The "stable air" that Garstang referred to is air that is layered, or stratified, by temperature with an inversion layer, like the air that traps smog closer to the ground in many cities. The stratified air and the inversion help to bend sound back toward the ground, therefore propagating it further along, said Garstang.

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