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自然科普文:动物年龄判断的一些方法 [Copy link] 中文

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Animals may not have birthcertificates, but they do display telltale signs of aging.


It seems like every year, theworld discovers a newest oldest animal.


Almost a decade ago, it was Ming, the 405-year-old clam. Then there wasJonathan, a giant tortoise who was touted as the world's oldest livingcreature—until questionslater emerged about his identity. There are accounts of 150-year-old whales and 115-year-old reptiles. They make Lonesome George—the famousGalápagos tortoise who died last year at 100—seem relatively young in comparison.


Determining the ages of these particular animals was not overlydifficult. Like all clams, Ming grew tree-like rings forevery year it was alive. Jonathan and George—the tortoises—were welldocumented, having appeared in diaries and photographs over the years. Thebowhead whale—called the longest-living mammal on Earth—was found with acentury-old harpoon pin lodged inside of it.


But determining the age of other animals—particularly those bornin the wild—is not such an easy task. Zoologists can take x-rays to look forgrowth markers in the skeletal structure. And they can easily find out how oldan animal is after death, by examining certain biological markers on anautopsy.


Withoutx-rays or tissue samples, however, determining the age of an animal becomes alot more difficult. Zoologists must rely on visual cues,with a little bit of guesswork thrown in. Below, a guide to what they look forin various species to determine age.


Orangutans Get Wrinkles Too


A lot of primate aging has to do with teeth, says MeredithBastian, curator of primates and small mammals at the Philadelphia Zoo.


"IfI look at teeth, I have a pretty accurate idea of how old an animal is,"she says.


Specifically, Bastian is looking at a primate's molars.Worn-down molars may indicate that a primate is older—or it may indicate that aprimate eats food that requires a lot of heavy-duty chewing.


Shealso looks at a primate's skin.


"There are indications that are very similar tohumans," says Bastian. "It's very clear—you can differentiate a babyversus a juvenile versus later stages of life, by looking at wrinklyskin."


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In wild male orangutans, zoologists look for somethingcalled a flange—or cheek pads—which are only visible on sexually maturedominant males. As they age and become over-the-hill orangutans, their flangessag—much like our jowls.


Butthat's not always 100 percent accurate, says Bastian, because unflangedsexually mature males also exist.


"Itused to be thought that only flanged males could mate because the flange helpsthem emit long calls to attract females," she says. "That's thedominant male strategy. Unflanged males have a sneakier strategy. Theybasically mate away from the flanged males and try not to get caught."

“人们曾经认为只有带凸缘的雄性才能得到交配,因为凸缘帮助他们发出长鸣声,以吸引雌性,”她说。 “这是雄性主导策略。无凸缘的雄性有一个隐蔽的策略。他们基本上远离带凸缘的雄性交配,尽量不被抓到。”

Femaleorangutans don't have flanges. They do wrinkle and lose bone density, much theway older humans do.
"Theymight have less hair if they're more stressed," adds Bastian.


Onelast marker? The whites of orangutan eyes. Babies have white circles aroundtheir eyes that disappear gradually over time. So if you can see whites itmeans that an orangutan hasn't finished weaning yet.


Another Use for Cat Hair


Fordating cats, you want to start out with the hair, says Tammy Schmidt, curatorof carnivores and ungulates at the Philadelphia Zoo.


"Hairgets dry and brittle and gray as it ages," she says. "That's true foreverything from house cats to big cats like an elderly lion ortiger."

她说,“随着年龄的变化,毛发变得干燥而脆弱并且发灰,” “从家猫到一个年长的狮子或老虎等大型猫科动物,都是如此。”

Ofcourse, you don't want to get too close to an elderly lion or tiger. But it ispossible to see changes in their fur coats from a distance.


"Thehair becomes duller," says Schmidt. "A cat is going to take less careand time with their fur coat [as it ages]."


Thereare other clues, but they may be harder to see.还有一些其他的线索,但是可能很难能被观察到。

"Acarnivore like a lion or tiger is made to be secret and sly about what'shappening to them," says Schmidt. "You need to put all of the piecesof the puzzle together."


Thosepieces include things like muscle tone—animals become less toned as theyage—and how the tail fits between an animal's hips.


"You look at how full the rump is," she says."Can you see ribs? You look at how they're moving. Older animals are goingto have more pronounced stepping because their eyesight is diminishing."

“你可以观察它们的臀部是否饱满”她说。 “能不能看见肋骨?看看他们是如何移动。年长的动物将会有较明显的踏步,因为他们的视力变得衰退。”

Only Dead Fish Admit Their Ages


The secret to aging fish is in the ear, reveals Kara Hilwig, thesupervisor for the Alaska State Fish and Game lab. Hilwig was part of the teamwho recently aged a 200-year-old rockfish captured in Alaska.

鱼的年龄的秘密在它们的耳朵里,Kara Hilwig揭示了这一秘密。

To age the rockfish, Hilwig sliced through the animal'shead and removed two tiny ear bones called otoliths. The otoliths have annualgrowth rings—like a clam or a tree—which can be counted to determine how old afish is.

为了确定石斑鱼的年龄,Hilwing 切开其大脑取出鱼耳石,这种耳石像树和蛤蜊一样具有年轮,可以通过这些年轮来确定鱼的年龄。

Onecaveat: The fish must be dead.


"Webreak the bones in half and then put them over a flame," says Hilwig. "Andthat's how you can discern this annual feature."
Want to age a fish without slicing its head off and diggingaround for ear bones? You're out of luck, she says.


"Itwould be very hard to determine a fish's actual age without the otolith,"she says.


It's also important to make sure fish live in an environmentwhere temperatures fluctuate. The otoliths only grow in the summertime.



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