水獭 : 吃货的基本功

Otter Touch

Sea otters are pretty petite compared to other marine mammals. Which means that, despite their fur coats, they tend to lose heat quickly, and need lots of energy to stay warm.

"So they need to eat 25 percent of their body weight each day." Sarah McKay Strobel, a sensory ecologist at U.C. Santa Cruz. "But in order to eat that much food, that means sea otters need to find all that food. And that's where we come in."

She and her team studied the otter's senses, to solve the mystery of how they're such efficient foragers. Vision isn't reliable, she says—it's pretty dark and murky underwater, and crabs and clams tend to hide. Hearing is also tough for otters, in the noisy underwater environment. And sniffing's no good either. "When they're underwater they're holding their breath."

What's left is touch. So Stroble and her team measured the sensitivity of the otters' paws and whiskers. They blindfolded an otter named Selka, then presented her with plastic plates engraved with tiny grooves, like corduroy. Selka's job was to select the plate with two-millimeter grooves, which she'd been trained to associate with tasty shrimp, instead of plates with differently sized grooves.

Turns out, Selka could perceive just a quarter millimeter difference in the grooves' width with her paws—above and below water—and half a millimeter difference with her whiskers. "The fact she was able to perform so well while moving incredibly quickly I think is really interesting and suggests that sea otters have very quick decision making abilities, and very quick sensory processing abilities, which makes sense when you think about the type of lifestyle they lead and how quickly they need to find food." The full details—and a cute photo of Selka—are in the Journal of Experimental Biology.

For the record, humans can feel the difference too, but it takes us 30 times longer. Which might make sense. After all, we evolved in environments where touch was less important in a hunt than were sight and sound.

参考译文

与其他海洋哺乳动物相比,水獭体型相当娇小,这意味着,尽管穿着毛皮大衣,但它们还是常常会热量流失过快,需要摄入大量能量来保暖。

所以他们每天的食量相当于四分之一的体重,加州圣克鲁斯感官生态学家萨拉表示,但要想吃那么多,就得找到那么多食物,这就是我们研究的切入点。

她和团队研究水獭的感官,以研究水獭何以高效觅食。她说,在水下,视力是不可靠的,水下阴暗浑浊,螃蟹和蛤蛎往往隐藏较深。在嘈杂的水下环境中,水獭想靠听觉也很困难。嗅探也不好使,水獭在水下会屏住呼吸。

剩下的是触摸。所以萨拉和团队测量了水獭的爪子和胡须的敏感性。他们蒙住了一只名叫赛尔卡的水獭,然后给它看了一个像灯芯绒似的刻有小凹槽的塑料盘子。赛尔卡的任务,是选择两毫米的、而非其它尺寸的凹槽板,经过训练,如果选对,它就可以吃到美味的虾。

结果,不论水上水下,赛尔卡都能查觉出凹槽宽度的区别,用爪子可以精确到四分之一毫米,用胡须可以精确到半毫米。萨拉说,水獭发挥如此之好,动作快得惊人,真的很有趣,这表明海獭有非常快速的决策能力和感官处理能力。这也就很好地解释了它的生活方式,以及它们为何能迅速找到食物。完整的实验细节和赛尔卡的萌照都发表在实验生物学杂志上。

郑重声明,人类也能感受到差异,但人需要花的时间是水獭的三十倍。这可能也有它的道理的。毕竟在我们进化的环境中,相比视觉和听觉,触觉对觅食并不那么重要。

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