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If you consider yourself a romantic, you may use music or songs to express your feelings. You may know that animals also often use music and songs to set the mood. Birds woo their mates with songs, and even gorillas and bears can sing a tune. But recently, scientists studying frogs in the rain forests of the Southeast Asian island of Borneo found that the male tree frog actually plays an instrument to find his companion.
This one-inch tree frog mates and breeds in hollowed-out tree limbs, which resemble organ pipes. Frequent rainfalls fill these openings with water. When the frog enters his new tree hole, he gives a peep and listens, then changes his pitch and peeps again. With each call, the frog can adjust his pitch to increase the volume it hears inside the tree hole.
Every tree hole, like every organ pipe, has a certain volume and shape. And, for each shape, there is a small set of sound frequencies that fit that shape exactly. This exact fit is called "resonance frequency." By altering his pitch, the frog is trying to get this resonance effect. He is literally "self-tuning" by raising and lowering his pitch until he finds the frequency that resonates in his tree hole. When he resonates, he gets the perfect volume. According to scientists, the male frogs that reach the perfect volume often get female frogs knocking on their trees.
To test their theory, scientists placed a frog in a plastic pipe with some water. The frog peeped. Then, they changed the level of water, and thus the volume of air in the tube. Each time they changed the water level, the frog changed his pitch to match the tube's new resonant frequency.
There are other species that build loudspeakers to get more volume for their mating call. Some frogs and crickets dig holes to specific shapes or cut holes of particular sizes in leaves to achieve maximum sound. But the Borneo tree frog is the only known animal that can change its own pitch for peak performance.
So, the next time you're humming your favorite tune in the shower, and you reach the perfect pitch, look out—a female tree frog may come knocking on your door!
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