Jumbo's underground telephone

kw: book reviews, nonfiction, natural history, african elephants

We joke about keeping one ear to the ground. Old Western films show an Indian guide putting an ear down and telling how many and how far away a war party is. As a Geology student, I heard occasional reports of people camping who heard a rattling or banging sound just before feeling the shaking of an earthquake—I guess they were using a rather thin pillow!

Also, as a Geology student, I took the requisite Geophysics course. For a couple of weeks, a bunch of grungy kids tramped about a meadow near campus, laying out geophones and banging a metal plate with a sledge hammer while running a multichannel chart recorder (no digital equipment in 1970). Eventually, most of us figured out that there was a water pipe buried about nine feet down. One or two claimed they could hear the thumps if they got a couple hundred feet away and put their ear to the ground. I reckon they could. None claimed to hear the smaller echo from the pipe.

About ten years ago, Caitlin O'Connell and a couple of colleagues published the first monograph (O'Connell, Arnason, & Hart, 1977 in The Journal of the Acoustical Society of America) describing African elephants' use of seismic signals, "sound in the ground", to communicate farther than their rumbling voices can carry through the air.

Continued work showed that the gel pads in elephant feet, and others between shoulders and head, resemble the "melon" in dolphin heads, that is used to focus sound and transduce between bone and water or air for better sonic efficiency. Also, elephants have an ear flap that they close when listening "below". To sense ground signals, an elephant usually lifts one forefoot, rises onto the toes of the other, and closes the ear flaps. Sound is then efficiently transmitted through the leg bones to the bones around the ear. With both legs on the ground (on tiptoe), the evidence is pretty strong that the animal can determine direction.

In The Elephant's Secret Sense: The Hidden Life of the Wild Herds of Africa Dr. O'Connell narrates her studies of elephants and discovery of seismic listening over several field seasons in Namibia beginning in the early 1990s. Good science is a detective story, and this one is first-rate.

The author and her partner (now husband) Tim Rodwell began with a 3-year grant they almost stumbled onto while taking a break in Africa, before beginning PhD work. They were to study elepants in and near the Caprivi Game Park, with the main goal of reducing elephant depredation on the people's crops...and their fatal retaliation. It was during this period that she first noticed the tiptoe listening behavior that led to her discovery.

Between this study, finishing their PhD work, and further studies in Caprivi and at Etosha National Park, they and a number of co-workers gathered great amounts of data on the relationships within elephant family groups, both matriarchal herds and smaller bull "clubs"; learned that elephants recognize voices, by their differing responses to alarm calls, whether they came from "someone they knew" or not; and determined that an alarm call heard only seismically (through the ground) resulted in alertness, but little excitement.

In the midst of it all, it was easy to observe that elephants are as individually different as people. They are playful, moreso as calves, but somewhat at any age. The amount of bull jousting that goes on has a lot to do with how secure the larger bulls feel, having more to do with personality than with brute strength.

Caitlin and Tim have established an educational and fund-raising organization known as Utopia Scientific, and carry on their studies in Africa and at their American campuses.