Trivia & Beyond: Why are Female Hyenas Bigger than Males?

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In the 1960′s the chimpanzee expert, Jane Goodall, arrived in the Ngorongoro Crater expecting to dislike Spotted Hyenas. However, it did not take long for them to win her over. “Hyenas are second only to chimpanzees in fascination,” she wrote; “they are born clowns, highly
individualistic.”

It was not just her who had a fascination with these creatures. In fact, they continue to capture the imagination of many. Most people have a fairly warped idea of hyenas; largely due to the fact that a huge percentage of those interested in African wildlife have seen the Lion King. The Lion King did for hyenas, what the movie Jaws did for the Great White Shark. But, spend some time with these creatures and you will find out that there is just so much more then meets the eye…

 

The protective mother standing guard at the entrance to the den

Recently I stumbled upon an article by Steve Kemper in the Smithsonian Magazine. It included the most fascinating research. Below is a snippet of one of the more fascinating aspects of hyena life.

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. You have to believe me when I say that you can sit two 6-month-old cubs side by side and the one could be twice as big as the other, purely because of having a mother ranked No. 1 and the other ranked No.19.

 

The two cubs just can’t get enough of climbing all over mom

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. 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.

 

As they get older so their confidence grows and they move further and further away from the safety of the den

At Londolozi we have a very healthy population of Spotted Hyena and every once in a while we get to view them at a very young age. They are the most adorable things to watch as they play around the den-site. What I love, however, is the fact that there is so much complexity within this species. There is so much going on. They are for example, a species in which the female is completely dominant and both larger and more aggressive than the males. In 2008 a new theory was developed by Holekamp to try explain this. To end off, I thought I would include a passage of hers which she used to explain the evolution of hyenas’ female-dominated social structure and odd reproductive apparatus…

“I think the bone-crushing adaptation is the key to it all.” She explains: Spotted Hyenas’ ancestors evolved massive skulls, jaws and teeth so they could pulverize and digest bones. This gave them a tremendous advantage over other predators, but with a cost: the skull and jaws that make bone-crushing possible take several years to mature.

Holekamp has found that young hyenas can barely crunch dog biscuits. Hyena mothers care for their cubs for three or four years, much longer than most other predators do. Alone, cubs would be unable to compete for food at kills. “That put pressure on females to give their kids more time at the carcass,” says Holekamp. Females had to become bigger and meaner, Holekamp hypothesizes, which they achieved partly by boosting their “masculinized” hormones.

If Holekamp is right, female dominance and matriarchy among Spotted Hyenas stem from evolutionary adaptations made for the sake of feeding the kids.

 

Putting the cubs back into the den

Written, filmed and photographed by Adam Bannister
Inspired by the work of Steve Kemper and Kay Holekamp of the Smithsonian Institute

Adam Bannister
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