The center of a spotted hyena clan's social life is the communal den. A pregnant hyena goes off alone to give birth, then moves her cubs to the den when they're a month old. The den is usually adapted from a hole dug by aardvarks or other small animals, and has multiple entrances connected by tunnels dug by the cubs. The earth around the den is quickly worn bare by frolicking cubs and lounging adults. The cubs spend eight months there with the clan's other youngsters—a dozen at a time isn't unusual, and Holekamp once saw a den with 22.
One early evening at the den of the Fig Tree clan, half a dozen hyenas are lying in the grass around the entrance. Holekamp, Cokayne and a graduate student named Sarah Benson-Amram, who's been living at the camp for a year, can recognize more than 100 hyenas from the Talek and Mara River clans, identifying them by their shoulders, ears, faces or sides. But they are just getting to know the Fig Tree group. A cub named Figaro, young enough to still have black fur, emerges from the den and gets licked all over by its mother, Carmencita. Bigger cubs with new spots—they start to lose their black baby fur at six weeks of age—boil out of the den and romp around, pawing and nipping each other. One of them grabs Figaro by the ear and pulls the small cub over. The other three play tug of war with a stick, rehearsal for future battles over a topi's haunch or a gazelle's torso. An older cub nudges a sleeping female named Fluffy, who jerks her head, a warning. The cub jumps back but tries again, shoving its head into Fluffy's belly. "She's managing to introduce herself," says Holekamp.
Hyenas have a complex behavioral language. Casual hellos include nuzzles, muzzle licks and body rubs. More formally, and nervously, a subordinate animal will lift its hind leg to expose its erect penis or pseudopenis for the dominant animal to sniff or lick. Other deferential gestures include giggling, head-bobbing and groveling. Males are the principal appeasers, says Holekamp, "because they stand to lose a lot"—status, access to food and mating—"if their relationship with the girls gets messed up."
As the sun lowers, more hyenas return to the den. An adult named ET puts her head into the entrance. "She's groaning, calling her cubs," says Holekamp. ET backs partway into the den so her cubs can nurse without coming out. "She must have really little ones hiding in there," says Holekamp. Moments later a tiny black head pops up behind ET, then quickly ducks back inside. "Too scary," says Holekamp. "Too many hyenas out here."
A series of high whoops comes from our right, homecoming signals from two cubs who've been on an excursion with five adults and two subadults. One of the new subadults lunges at Fluffy, who bares her teeth. The teenager retreats but returns seconds later with a teenage ally. They stand stiffly over Fluffy, muzzles pointed at her, tails bristling.
"Poor Fluffy," says Holekamp. "She's just lying there, and this teenager picks a fight, then forms a coalition with another kid. Teenagers are insecure about their rank so they're always trying to prove it. Girls are particularly tenacious, because if they lose their rank, it can have lifelong consequences, so they're constantly picking fights."
Cubs enter life with their eyes open and some of their teeth erupted, and within minutes siblings are fighting one another to establish dominance. The mother has only two nipples; in a litter of three, the least aggressive cub will usually starve. Cubs inherit their mother's rank, and the higher it is, the more likely her cubs will reach adulthood and reproduce: status ensures powerful allies, extra protection and a bigger share of the food. The effects of a mother's status can be stark. Holekamp has a photograph of two 6-month-old cubs sitting side by side. One is twice as big as the other—the difference between having a mother ranked No. 1 and No. 19.
A recent study by Holekamp and her colleagues suggests that status begins in the womb. They discovered that in the final weeks of pregnancy, high-ranking females produce a flood of testosterone and related hormones. These chemicals saturate the developing cubs—both males and females—and make them more aggressive. They're born with a drive to dominate, which presumably helps them uphold their matrilineal status. By contrast, a pregnant subordinate female produces a smaller spike of hormones, and her descendants become subservient. Holekamp says this is the first evidence in mammals that traits related to social status can be "inherited" through a mother's hormones rather than genetics.
Perhaps the most perplexing question about hyenas is why females have pseudopenises. The structures complicate mating and birth. The hyena's reproductive canal is twice as long as that in a similarly sized animal, and what's more, there's a hairpin turn halfway to the uterus. "It's a long gantlet for sperm to run," says Holekamp. It's also an ordeal from the other direction. Among the first-time mothers in captivity, according to the Berkeley researchers, 60 percent of cubs die during birth, most from suffocation after getting stuck in the birth canal. Subsequent births are easier.
Surprisingly, the pseudopenis doesn't appear to be a side effect of the hormones a female is exposed to in the womb. In other mammals, testosterone-related hormones can masculinize a female fetus's genitalia. But when the Berkeley researchers fed pregnant hyenas drugs that blocked the effects of testosterone and related hormones, the female cubs were still born with pseudopenises.