FIT TO BURST

INFLATION IS A USEFUL TOOL IN NATURE, ALLOWING ANIMALS TO PROJECT SOUNDS, SCARE OFF PREDATORS OR EVEN ATTRACT A MATE. LET'S BRING ON THE BLOAT!

- JULES HOWARD

BUILT-IN BAGPIPES

CALAKMUL BIOSPHERE RESERVE, MEXICO

This painted tree frog produces a piercing screech that differs slightly in pitch to closely related species. To maintain the call for as long as possible, it squeezes the same breath of air back and forth across the larynx, creating trilling sound. This is just one of thousands of different kinds of frog calls, each unique to its own given species. “Vocal sacs differ enormously across frogs," says herpetologist Dr Mark Scherz of the Natural History Museum of Denmark. “Some species have single sacs, some have paired sacs, some sacs even expand substantially down the body or expand hugely in front of the head.”

Even female frogs have taken to inflation. Last year, scientists in Minnesota discovered that female green tree frogs inflate their lungs to cancel out the calls of rival species. The exact mechanism that causes this noise-cancelling effect is yet to be fully understood, but it is likely to help females locate males when multiple species congregate together at breeding ponds.

HELLO, CHUBBY CHEEKS

SOUTH DAKOTA, USA

In birds, the voice box (called the syrinx) is double-barrelled. Some species, such as the greater sage grouse, also have a pair of vocal sacs, kept within a flexible throat pouch. As soundwaves escape from the syrinx they resonate against the elastic membrane of each sac which, as it inflates, is pulled taut like the skin of a drum. The throat pouch can also be brushed against the feathers on the wings to make a dramatic whooshing sound.

The resulting courtship noises are what evolutionary ecologist Prof Gail Patricelli calls a "swish, swish, coo, pop, whistle, pop," performed while the male struts in front of potential mates.