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Cassowary Calls
Introduction
It's hard enough to study animals in the wild when they're easy to find. But some of them make life more complicated by being notoriously shy. In this Science Update, you'll hear about efforts to study the rare and often inaudible call of an elusive bird.
Podcast
Cassowary Calls
Transcript
A bird with an earth-shaking sound. I'm Bob Hirshon and this is Science Update.
(Audio: sound of rain forest)
In a rain forest in Papua New Guinea, a deep, rumble penetrates the dense vegetation.
(Audio: cassowary call)
It's the call of a cassowary—a large bird that looks something like an emu, with black feathers and a wattled, red-and-blue neck. Andrew Mack, a researcher for the Wildlife Conservation Society, says they're tough birds to study.
Mack:
They're black and they just sort of slip into the shadows. So, even after years of working with them, you don't observe much about them. They're hard to estimate how big a population is or anything. But they do call occasionally.
Mack and his colleagues recorded cassowary calls and analyzed them. They found that some frequencies of the call are very low—below the level of human hearing.
Mack:
And then that's interesting because those low frequencies travel better through rain forest or through vegetation. So a low frequency is sort of ideal for birds to hear another bird at a greater distance.
Mack says knowing that cassowaries make these super low frequency calls could help scientists estimate how many birds there are—the first step in figuring out how to manage their population. I'm Bob Hirshon for AAAS, the Science Society.
Making Sense of the Research
It's hard to protect a species if you don't study it, and it's very hard to study it if you can't find it. But that's precisely the problem with the cassowary: in the wild, these birds are very reclusive and survive by making themselves hard to spot.
Mack decided that the best way to study them was to listen for them, rather than to look for them. Recording and analyzing their calls may help him map out the distribution of the cassowary across New Guinea (and parts of Australia), and whether any particular population is threatened.
Capturing the cassowary call requires patience. Because the birds call infrequently (hours may pass between single calls), they can't just flip on a tape when they hear a call starting. So they set up a recording system in the rainforest, crank the sensitivity way up, and block out the higher frequencies that might interfere with the cassowary call. It was during these recording sessions that Mack discovered that some of the cassowary's calls are below the range of human hearing. In fact, it's often easier for a human to feel the call of the cassowary than to hear it: one researcher compared it to a small earthquake.
The communication strategy makes sense for a large, somewhat ungainly bird that might be an easy target for predators. By communicating through vibrations in the ground, they can keep their whereabouts secret from animals that are more attuned to images and sounds. Also, low-frequency vibrations carry much farther through the ground than higher-frequency sound waves can travel through the air. So in addition to the security, the cassowaries enjoy greater long-distance coverage.
Cassowaries aren't the only animals that communicate through low-frequency signals. Many other animals, from elephants to kangaroo rats, are known to communicate with each other by foot-stomping. The vibrations announce an animal's location to others of its species, and can even point the way toward fresh water or other desirable destinations. Many marine mammals, like whales, communicate using low-frequency vocalizations that propagate through the water. By studying these forms of communication, scientists can get a more accurate first-hand account of where the animals are and what they're doing.
Now try and answer these questions:
- Why is the cassowary hard to study?
- What are the advantages of the low-frequency communication system that it uses?
- What information might be gathered by studying a cassowary's calls?
- Can you think of other animal communication systems that differ from the channels used by humans?
Going Further
Rainforest Australia has this information page on the cassowary.
Stanford University published this article on foot-stomp communication in elephants.
Woods Hole Oceanographic Institution offers this article on low-frequency communication in marine mammals.
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