The life story of a hyena.

News and commentary about environmental issues.
April 12 2010 7:07 AM

Sad Yowlers?

The story of the hyena.

More revolting creatures: the eel, the skunk, the snapping turtle, the vulture, the tick, the jellyfish, and the slug.

Hyenas at the Masai Mara National Reserve.
Hyenas at the Masai Mara National Reserve

Is there any other mammal that people find as despicable as the hyena? If a creature is furry and nurses its young, usually we're willing to admit some mammalian fellow feeling. Among furred creatures, only the rat vies with the hyena for most loathed.

Hyenas, particularly the African spotted hyena, with its massive jaws, hulking shoulders, and startling laugh, have been terribly misunderstood. The creatures may not be beautiful, but they don't deserve contempt. They are intelligent and gregarious with a well-organized social system of clans patrolling discrete territories. The clans are ruled by females. Maybe the female hyenas gain a little extra authority or assertiveness from the surprising fact that male and female hyenas have nearly indistinguishable external genitals, about eight inches worth. Their appearance has aroused amazement, confusion, and sometimes disgust.

But the hyenas' primary public-relations problem is that laugh. To the unprejudiced ear it sounds like a chortle or a giggle, but many human beings hear it as a maniacal cackle; the hyenas are laughing because they have an evil plan. In fact, the distinctive sound occurs when the animals don't have access to something they want; it's an expression of excitement mixed with frustration. Variations in the pitch also say something about the laugher's age and social status. Hyenas have one of the richest vocal repertoires of any terrestrial mammal, primates included. The laugh is one of many vocalizations, including a cheerful whoop that says, "I'm over here," and an affecting array of mother-and-cub groans and murmurs.

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Another disparaging belief is that hyenas are skulking scavengers, subsisting on what's left over from the kills of the glamorous predators—lions and leopards. Hyenas, the most numerous predators in the savannas of sub-Saharan Africa, are in fact excellent hunters. Three-quarters of their diet comes from large hoofed animals they kill and digest with astounding efficiency. Their massive molars pulverize bones; hair, teeth, and hooves are regurgitated later. A few hyenas can reduce a 400-pound African Cape buffalo to a pair of horns and a patch of blood on the ground in less than an hour.

(In any case, scavenging is an honorable and essential profession. Lions hunt, but they're not above consuming prey that was slaughtered by somebody else. Almost every other carnivore, including human beings, does the same.)

The female hyena's faux penis may be amazing, but it is not efficient. In fact it ranks with the human knee as one of evolution's truly bad designs. It's through this elongated clitoris that the female urinates, mates (with great difficulty for the male), and—ouch—gives birth. She even has a sham scrotum—fused labial tissue with no payload.

Seriously misled, Aristotle concluded that all hyenas were male, which would be a drawback for the species. Ernest Hemingway believed that every hyena possessed both male and female organs. His mistake is the first word in a vivid description from the travelogue, Green Hills ofAfrica: "Hermaphroditic, self-eating devourer of the dead, trailer of calving cows, ham-stringer, potential biter-off of your face at night while you slept, sad yowler, camp-follower, stinking, foul with jaws that crack the bones the lion leaves …" (Hemingway liked to sit outside his tent and shoot them.)

A female hyena's internal reproductive organs are those of a normal quadruped. But her quasi-male external equipment makes birth painful and costly. The first cub—hyenas usually bear twins—is stillborn more than half of the time. The unlucky trailblazer moves along the straitened birth canal like a softball moving through a narrow party balloon. The death rate for newborns is a serious disadvantage, but there may be compensation. The females, all of whom are larger and more aggressive than any male, make sure that their young have priority at the kill. (Among the lions, males eat first and swat the cubs away.)

At first scientists believed that the masculinization of the female hyena had one simple cause—a big dose of male hormones delivered in utero. (One of these is androstenedione, which you can buy at health food stores, and is one of the substances that helped Mark McGwire's home-run totals.) Further research found that even when dosed with drugs that blocked the male hormones, the females emerged with external genitalia unaffected (PDF). It turns out that the female hyenas' hormone receptor has a mutation that causes it to misfire. It keeps sending the message of incoming male hormones even when they're absent. The same kind of mutation may be the culprit when human prostate cancer, male-hormone-driven, fails to respond to the usual drugs.

The effect of hormones on fetal development is one thing Stephen Glickman, UC-Berkeley professor emeritus of psychology, has been studying at the hyena colony he founded in the mid-1980s. (The Masai herdsmen who took Glickman to the burrow in Kenya to gather cubs were disappointed when he didn't want to take hundreds, only 20, back to Berkeley.) His fellow authors on research papers include a developmental biologist with an interest in prostate cancer and a pediatric urologist looking for the causes of human genital anomalies.

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