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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."
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."
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."
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.
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.
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.