L. Smale

Kay E. Holekamp, a zoologist at Michigan State University, writes from the Masai Mara National Reserve in Kenya, where she is studying the behavior of spotted hyenas.

Monday, June 27

A couple of days ago my students and I darted a young adult hyena named Dionysus. This is a particularly interesting animal, as it is the youngest adult offspring of our last alpha female, Murphy, who was killed by lions in April. Murphy’s youngest adult male offspring will almost certainly disperse voluntarily to a new clan within the next year or two, but her youngest adult daughter should remain throughout her life in her natal social group, called a “clan,” and take over there as the alpha female. In the latter case, assuming this animal is able to fend off attacks from its very brawny older sisters, Juno and Loki, Dionysus will rank first in a clan of more than 90 hyenas! If Dionysus ranked first, she would be able to usurp food from any other hyena in the clan, live a long life and produce more surviving offspring than any other female.

H. E. Watts

Although spotted hyenas are notoriously difficult to sex, my students and I are typically very good at determining the sex of hyenas using a variety of subtle morphological cues as they move around or engage in “greeting ceremonies” with one another. However, every once in a while a hyena fools us, and an individual believed to be a male for two or three years one day shows up nursing cubs at the den! None of us had ever been able to sex Dionysus with complete certainty, even though this animal will be 2 years old in a few weeks. We had all thus been looking forward to darting Dionysus because we expected this animal would be easy to sex once we could examine it very closely. However, this time, even after the animal fell asleep and we rolled it over so we could examine its genitalia, we continued to get mixed messages.

Christine Drea

One of the most peculiar things about spotted hyenas is the fact that both the behavior and the morphology of females are very heavily “masculinized.” In contrast to a vast majority of mammals, including other hyena species, female spotted hyenas are substantially more aggressive than males, and they are also socially dominant over males. Females are roughly 10 percent larger than males, and this too is a pattern reversed from that seen in a vast majority of other mammals. In these and many other respects, spotted hyenas appear to violate many of the accepted “rules” of mammalian biology. The external genitalia of the female spotted hyena are so similar to those of the male that for centuries people believed these animals to be hermaphrodites. In contrast to other female mammals, including female striped and brown hyenas, the female spotted hyena has no external vaginal opening. Instead, the female’s clitoris is greatly elongated to form a fully erectile “pseudopenis” that is nearly indistinguishable from the male’s phallus. The phalluses on both male and female spotted hyenas are the same length, and differ only in the shape of the tip, which is blunt in the female but pointed in the male.

Kay E. Holekamp

Astonishingly, the female spotted hyena urinates, copulates and gives birth through her pseudopenis. When she gives birth to her first litter, the posterior surface of the female’s pseudopenis tears and leaves a long patch of bright pink scar tissue. Although we hyena-watchers find this very handy for determining whether a female has ever borne a litter, the tearing must hurt like the devil. In addition to having a fully erectile pseudopenis, the female has vaginal labia that are folded over and filled with fat and connective tissue to form a structure that looks remarkably like the male’s scrotal sac. When I examined the “scrotal sac” of Dionysus this week, the masses of fat and connective tissue were so turgid that I thought I was palpating real testes. Therefore I initially declared this animal to be a male. However, several minutes later I was forced to change my mind.

We had been handling Dionysus for over 30 minutes when I finally noticed that its nipples were distinctly enlarged. It was only this trait that allowed us to determine with absolute certainty that this animal was in fact a female. Although both male and female hyenas have nipples, those of pre-reproductive females, and those of males of all ages, are only a couple of millimeters in diameter. The nipples of this particular hyena were over 15 millimeters in diameter, indicating not only that Dionysus is a female, but also that she is probably already pregnant with her first litter! One small mystery solved! Now we will need to monitor aggressive interactions among Dionysus and her sisters very closely to determine whether she will indeed be able to hold onto the alpha status she should have inherited when her mother died.