飞鼯猴能滑翔飞出平均约30米的距离，但是科学家最近发现，滑翔比四肢着地走过去要多消耗1.5倍的能量。那么为什么它们还要滑过去呢？哺乳动物演化出滑翔能力可能是为了生存，也能帮助它们逃脱捕食者。 

More than 60 mammal species—like the famous flying squirrel—have adapted the ability to sail from tree to tree. Thrilling, yes. But what’s the evolutionary advantage?

One theory suggests gliding saves energy. So researchers tested that idea using colugos—mammals from Southeast Asia that turn into giant skin sails when they stretch out their legs.

The scientists placed accelerometers onto the backs of six compliant colugos. The data packs revealed that each colugo glided an average of a quarter-mile each night. But gliding isn’t as effortless as it looks. The researchers’ calculations suggest that flying actually requires one and a half times the energy of a conventional traverse. That’s because colugos prepare for a launch by climbing higher up the tree. And climbing’s a lot more strenuous than walking. Those findings appear in the Journal of Experimental Biology. [Gregory Byrnes et al., "Gliding Saves Time but Not Energy in Malayan Colugos" (citation to come)]

So why do it? The upside is speed. Colugos can sail 10 times faster than they can tightrope through the canopy. Which leaves more time to snack. Plus, leaping into the air is an easy getaway from predators. In the end, it’s not too different from human flight—costs more, but way faster.

—Christopher Intagliata