Hyena: Party animal or wallflower?

While my recent rant about misuse of taxonomic terms regarding "bugs" was meant to be largely tongue in cheek, there are some instances of identification faux pas that really do bother me, especially when they come from supposedly credible sources. The other day I was watching the "Meat Eaters" episode of "Life of Mammals" and was very displeased with David Attenborough, who referred to a brown hyena (Hyaena brunnea) as a "dog." This is extremely incorrect. I think that hyenas are easily one of the most interesting groups of carnivores in many ways, including their morphology, behavior, etc etc, and they deserve a closer look.

So, if a hyena is not a canid, what is it? Hyaenidae is actually one of the most recent carnivore families, originating around 10 million years ago in the Miocene epoch. Fortunately, there is a fairly good fossil record that we can use to trace how the hyena lineage began and developed over time. The earliest known specimen, Protictitherium gaillardi, resembled a modern civet. It had retractable claws, and is thought to have spent much of its time in trees.

Over time, early hyaenid populations spread into Europe, where we find the insectivorous Plioviverrops around 4-5 mya. Soon thereafter the first "running hyenas" appear, and there was a wide radiation of hyaenid forms that peaked during the Pleistocene, with 4 genera and 9 species extant at the same time. Here is an excellent resource that details many of the fossil remains and gives a great look into how diverse this family was at one time (insectivores, "jackal-like" forms, bone crushers, etc).

Today there are only four species remaining in the family: the aardwolf (Proteles cristata), the brown hyena (Hyaena brunni), the striped hyena (Hyaena hyaena), and the most-studied species, the spotted hyena (Crocuta crocuta). (Now many people put the brown hyena in its own genus, Parahyena, but there doesn't seem to be an absolute consensus on this issue yet, although it could be an artifact of much of the available literature being published before the switch, I need to dig out the citation for the paper that actually suggested the switch).

While these carnivores have many unique morphological features that impact their lifestyles and ecology, what I find most fascinating about this family is the wide range of social behaviors displayed between the different species. The aardwolf is significantly smaller and more gracile than the hyena species (it used to be in its own family, but was sunk into Hyaenidae). They are socially monogamous (although extra-pair copulations do occur), and there is extensive paternal care. These animals are not gregarious. Each pair pretty much keeps to itself, and during the non-breeding season they are mostly solitary. (Random trivia: the aardwolf has five digits on its front feet, as opposed to the four found on the other three hyaenid species).

In contrast, the spotted hyena is extremely social, with clans of up to 100 members (although this is an extreme). This species is often an object of fascination because females have genitalia that mimics male organs. Females are dominant over males, and it is thought that increased testosterone results in both their aggression and their unique anatomy. None of the other species of hyena have this morphology. Males are transient in these matrilineal societies, but females are largely philopatric and maintain strict hierarchies and complex relationships among themselves, with relatively little contribution from father after copulation. They raise cubs in either private or communal dens, and although twins and sometimes triplets are common, siblicide is frequent.

The aardwolf and the spotted hyena seem to represent two ends of a continuum: monogamous with relatively solitary lives outside of breeding season versus complex hierarchal societies with transient males. Interestingly, the brown and striped hyenas tend to fall somewhere in the middle.


Brown hyenas (my personal favorites out of the bunch) live in small groups, around 5-15 members that are mostly female, but there are often a couple of males that help to defend the group territory as well. Interestingly, the females mate with nomadic males and largely shun copulation with the residents. This makes sense because resident males are more likely to have been born in the territory, and are thus more likely to be close relatives to the females.

Striped hyena groups are small, and are mostly formed from a breeding pair and their offspring (although offspring from multiple seasons are often present). A point about this species that seems particularly relevant is that within their small family groups, individuals of the same sex associate much more with each other than with the opposite sex, to me it seems to be a social system that, whatever the reason for the differential interactions, could be a model for a precursor to the sharply divided roles between sexes in the spotted hyena.

So there are hyena social systems in a nutshell. There is much more to say about these fascinating animals, Lioncrusher's Domain has excellent information about all the species (and it gives great coverage of other carnivores too, definitely a bookmark-worthy site!). There is tons of literature on the spotted hyena, but the information on the other species is much harder to come by. I am extremely interested in intraguild predation, and hyenas have an important role in the complex pattern of interactions between carnivores on the African plains (something within this area of study would be my dream project for graduate school!).


(Image credit for aardwolf, spotted, brown, striped).