Transcript:

Hippos - How Low Can They Go?ambience: HipposWe're listening to the sounds of hippos. And while these calls are impressive, even more remarkable are the sounds they make that you can't hear. I'm Jim Metzner, and this is the Pulse of the Planet.Hippos can be found submerged in the rivers of Eastern and Central Africa, their heads often just peeking above the surface of the water. Generally, they only venture ashore at night, but at this time of year, the weather's cooling down enough that they'll occasionally haul their three ton bulk out of the water, and spend some daylight hours on land, looking for food. William Barklow, a Professor of Biology at Framingham State College, believes that hippos might also use infrasound--sounds below the range of human hearing, as a form of long distance communication.Barklow: We, while we were in the field, heard these drum-beat like sounds; it's very much like standing in a parade and your diaphragm vibrates in resonance with the big bass drum. Well, we felt that feeling and barely perceptibly picked up the sounds of this low frequency-like drum beat sound.I've found that hippos often will herd in a pool, and then there'd be another pool down the river, maybe two or three kilometers down, and there seems to be an important communication between these groups. Hippos will chorus, these bellows and other sounds, and then you'll hear them way down river being answered by the next herd. Infrasound, these low frequency signals that we think hippos may be making, would be very helpful in these situations because low frequency sounds don't break up much over long distances.With thanks to William Barklow, I'm Jim Metzner, and this is the Pulse of the Planet.