Calls in the Wild

Midday sun scorches¹ the plains of northern Namibia, and a female elephant just coming into estrus² is making a racket³. With a rumble loud enough to rival a jackhammer⁴, she broadcasts her availability for mating. But gusty winds and turbulence⁵ created by heat shimmering through the atmosphere tend to break up the sound waves she generates, so her signal carries little more than half a mile. The odds⁶ are slim that a mature male in his own period of reproductive⁷ readiness will be close enough to hear her call.

Hours pass. Dusk settles over the flat sand veld⁸. Winds calm, and air near the ground becomes cooler than the warm air above it, effectively creating a channel for sound. Now the low-frequency end of the eager female’s cries can carry six miles in all directions, reaching the ears of elephants spread over a range of more than 110 square miles. The chance that a tall, strong mate will come swaggering her way is now a pretty sure thing.

To understand how elephants make the switch from local to long-distance calling, it helps to know something about weather. Wind and heat -- along with rough terrain and dense vegetation -- limit animal calling ranges because they disrupt sound waves. Wind can also be a problem for the receiver: Gusts⁹ blustering¹⁰ over elephants’ massive heads and floppy¹¹ ears can make it difficult for these distinctly non-aerodynamic¹² animals to hear any signal clearly. High frequencies (think bird whistles and chimp chatter) are even more easily disturbed than low frequencies (elephant rumbles and lion roars).

The link between weather and sound has long intrigued Michael Garstang, a University of Virginia meteorologist¹³ with a tool kit¹⁴ full of weather instruments, a detailed grasp of how atmospheric¹⁵ patterns can affect acoustics¹⁶ -- and a fondness for elephants.

Garstang became curious about whether elephants waste energy bellowing¹⁷ against the wind, or whether they take advantage of daily atmospheric changes that can boost bass tones like the woofers¹⁸ in stereo speakers. To find answers, he assembled a team of researchers and headed to Etosha National Park in Namibia, home to a healthy and growing elephant population. Hills and forests aren’t part of Etosha’s savanna¹⁹ habitat, so Garstang knew that weather, rather than terrain, would be the most significant environmental factor affecting the elephants’lowest pitched communications.

Daytime temperatures at the site rose to over 110, and the wind regularly blew at more than 20 miles an hour. In the evening, temperatures dropped below 40, and for hours the air was almost still. Ninety-six percent of the infrasonic²⁰ signals Garstang’s team recorded occurred in the cool calm between dusk and dawn. The greatest number of calls happened from an hour before sunset to three hours after, with another talkative period in the first two hours after sunrise.

Those early morning and early evening peaks in calls support the idea that elephants have indeed adapted their behavior to match patterns of change in the atmosphere. Garstang succinctly²¹ sums up his findings: “Elephants talk most when conditions are best.”

That adaptation is crucial, since calling range helps determine the size of the area used by elephants at any given time. Long-distance vocalizations keep group members bonded as they trade information about resources and dangers and seek breeding partners across pachyderm²²-scale areas. Knowledge about how elephants communicate, Garstang says, can help us protect their habitat -- and their future.