More than 60 mammal species—like the famous flying squirrel—have adapted the ability to sail from tree to tree. [--1--], 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 [--2--] their legs.

The scientists placed accelerometers onto the backs of six [--3--] 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 [--4--] 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, [--5--] the air is an easy getaway from predators. In the end, it’s not too different from human flight—costs more, but way faster.
【视听版科学小组荣誉出品】
Thrilling stretch out compliant strenuous leaping into
飞行的代价 有60多种哺乳动物--比如说著名的飞天鼠--可以熟练的在树丛间滑翔。很酷吧！但是它们的进化优势是什么呢？ 有一种理论认为滑翔可以减少体能消耗。于是研究人员利用飞狐来验证这个想法。这种来自东南亚的哺乳动物在伸展它们的四肢时利用巨大的表皮进行滑翔。 研究人员在6只驯服的飞狐背部装上加速计。得到的数据显示每只飞狐每晚的平均滑翔0.25米。但是滑翔并没看起来那么容易。研究数据显示事实上飞行所消耗的能量是常规横穿的1到1.5倍。因为飞狐飞行时需要爬到更好的树上做起飞准备，而爬树比步行所消耗的能量要大得多。这项发现发表在《实验生物学》期刊上。 为何要爬树呢？因为越高速度越快。飞狐滑翔的速度是它们像走钢丝一样穿过树阴的10倍。这样它们就有更多的时间来吃东西。另外，滑翔可以轻松的甩开那些捕食者。最后一点，它们的滑翔跟人类飞行相差不大--代价更大，但是速度更快。