Thursday, July 31, 2008

The Dominance Hierarchy

One of the major reasons that we find spotted hyenas so fascinating is their social complexity. Hyenas operate under a linear dominance hierarchy that is extremely strict: no two hyenas share a rank, and it’s very clear who is dominant to whom (to them and to us). When a cub is born, it inherits a rank immediately below its mother, making it dominant to all its older siblings. Females will retain this rank throughout their entire lives, although how close this rank is to the top will decrease as more higher-ranking cubs are born (or increase as higher-ranking adults die). Males have a slightly shoddier deal, as is usually the case in this species. When a male is born, he inherits the rank immediately under his mother, just like a female cub. He keeps this rank for the first couple years of his life, while he’s still in his birth (or “natal”) clan. But once he reaches sexual maturity, he needs to disperse to another clan, because females from his natal clan won’t mate with him (high probability of incest—gross). So each male immigrates to a new clan at around age 2, and enters this new clan at the very bottom of the pecking order. He’s below all adult females, all cubs, and even below all the other adult males who have immigrated to this new clan. The only hyenas to whom he will be dominant are future immigrant males. This must be an especially tough blow to the ego to the son of an alpha female...

The first take-home lesson is that all adult female spotted hyenas are dominant to all adult males, because all adult males in a clan are immigrants. The females will be the first ones to point this out to you when you’re watching them—they are constantly putting the males in their place by being aggressive toward them or just ignoring them. The males, for their part, act the role—they tend to tiptoe around females, keeping their distance and acting very submissively.

The second take-home lesson is that when we say this hierarchy is “strict,” we mean STRICT. It dictates everything. Yesterday we saw one mother approach a den hole to try to nurse her cub, and when a higher-ranking mother (whose cub was in the same hole) saw this, she immediately walked over and snapped at the first mother, displacing her in the hole. After the first mother backed off submissively, the dominant mother walked away—she didn’t even want to nurse at that moment, she just wanted to make it perfectly clear that it was HER hole at that time. When the submissive mother made a move to approach the hole again, the dominant mother lunged at her, decisively ending the conflict. Eventually, they both lay down a couple feet from the hole, just staring at it.

Likewise, when the hyenas have killed a prey animal, such as a wildebeest, the highest ranking females and their offspring get to eat first. They are then followed by lower-ranking females/offspring, and finally by the adult males, who often stand near the kill looking longingly (and hungrily) at the carcass as all the choice cuts are devoured by their superiors. By the time these immigrant males get access, what remains is often just the skeleton—good thing hyenas can digest bone (more about that another day)!

What can be especially heartbreaking is that these adult males do much of the leg work (pun intended) when it comes to the hunting—and yes, hyenas hunt about 95% of their food—they don’t scavenge, as many mistakenly believe. Last summer we saw one male chase down a Thompson’s gazelle, eventually killing it. He had only taken a few bites when his higher-ranking brother came along, marched right up, and swiped the carcass. Because of the strict hierarchy, there was nothing the lower-ranking brother could do except watch as his brother ate the entire gazelle.

But it gets worse. Still hungry, this male proceeded to get himself ANOTHER meal, this time chasing down a juvenile gazelle (hunting is exhausting, so this is no small feat). Just as before, within seconds of biting into it, his brother showed up on the scene. He waddled over—his enormous belly, already full of the first gazelle, was definitely slowing him down—and promptly stole and ate this meal, too. You can imagine the torrent of expletives we let out as we watched this unfair sequence of events unfold. However, to the hyenas, it is more than fair, because everyone knows the rules, and everyone plays by them.

Important life lesson: if you’re low-ranking and you’re hankering for filet mignon, try to kill your prey in private, and then eat very, very quickly.

Up next: meet our alpha female, Murphy

1 comment:

Tom said...

Absolutely fascinating.

Happy to be human.


Michigan State University | College of Natural Science