The Spotted Hyena (Crocuta crocuta) is one of the most obvious, and to many people, the least attractive of the carnivores that inhabit the savannah grasslands of Africa. Most of us stop and take a few photos the first time we spot one wallowing in a mud hole, after which we tend to say “just a hyena” and rush on hoping to see if we can find a spectacular cat. Hyenas are close relatives of the cats and what you are missing is the remarkable biology and social life of these truly fascinating animals. They are carnivores with massive strong jaws that carry robust conical molars that can easily crack bones and their digestive system is so strong that they can digest bones and every part of animal except for hair and hooves. These they eat but then disgorge in a pellet. So, after reading this article I want you to stop the next time you come across a hyena in the Mara, try to identify the sex and status of the individuals you are looking at and understand what they are doing.
Females have a pseudo-penis
One of the most unique features of spotted hyenas is that the genitalia of the females have become highly masculinized so the females appear to have a penis – I say almost unique since I have since discovered that some mole species do the same. The females have no external vaginal labia, and the clitoris has developed into a pendulous organ that resembles a penis. This still functions and is used by the females for passing urine, giving birth, intercourse, and can even become erect and used to signal submission. The labia have become fused and form an organ that resembles the male’s scrotal sac. For some time, zoologists assumed that the masculinization of the female genitalia was a consequence of being exposed to male hormones (androgens) during development but recent experiments, where production of the male androgen hormones was blocked, show that this is not the case. Indeed, the female estrogen hormones play a critical role in both penile and clitoral development and determine the position of the urethral orifice. Of course, the obvious question is why? What advantage does this give the females and what selection pressure has resulted in the females developing this pseudo-penis? The answer is not apparent but may lie in their matriarchal and complex social life.
Matriarchal social system
The real fascination of hyenas is their large, socially complex societies that resemble more the behavior of large troops of baboons you see walking across the savannah than their closer carnivore relatives like lions. They live in clans that can include as many as 80 individuals, in areas where there are much prey available. These clans consist of multiple matrilineal lines – that means several female descendent lines with mothers, daughters, and granddaughters. These matrilineal lines are not closely related to each other and yet they form a coalition clan with groups of related individuals supporting each other within the clan. This is very different to lions where the prides consist of closely related lionesses and a coalition of males that are often related to each other but not to the females. Each female line is hierarchical within the clan, so that each daughter takes the rank of their mother and are dominant over low-ranking females irrespective of age and size. The high-status females start breeding at a younger age, reproduce more frequently and produce more cubs that survive better than the lower ranking females. Females give birth in remote dens but then move their young cubs to a common den, shared amongst the females of that clan and may accommodate as many as 30 cubs of different ages, derived from as many as 20 females. Since only some of the females are related, mothers invariably nurse only their own cubs and reject cubs from other litters. The cubs take a while to develop not weaning until 14 months of age, and are highly dependent on the mother for years in finding food. Young females usually stay with the clan, but the males leave their natal clans and join neighboring clans. The males do not carry the status of the mothers and join a new clan at the bottom of the pecking order. The males form their own hierarchy and status is determined by when they joined the clan and only get promoted when a male above them dies or moves onto another clan. Even so, females favor the incoming males as mates and they often form tight amicable relationships with a female that results in them getting mating opportunities.
The social ladder
All of the hyenas in the clan help to defend territories and when individuals from another clan appear they advance as a group with their tails and manes erect and often results in running battles. When they approach members of their own clan they do so in a ritualized manner, approaching face to face then raising their hind leg and letting the individual sniff their genital areas. Low-ranking females will often present an erect pseudo-penis in submission and in group situations only the dominant female will not have an erect pseudo-penis.
aggressive to both individuals with higher and lower ranks than their mothers but when a year old all their aggression is aimed at lower ranking animals. Mothers frequently support their young in being aggressive towards lower ranked individuals, and just like baboons, the young form coalitions to gang up against some individuals in an attempt to climb the social ladder. Scent is important and they spend much time sniffing each other’s genitals. They produce a thick paste from their specialized anal glands that they smear on grass and vegetation along the clan boundaries and within the territories and this strong scent identifies both clan members and individuals.
The clans act as a “fission-fusion group” that will come together in and around the den, defend the territory as a single unit, often hunt together but then will break apart and small subgroups or individuals will hunt alone. The hyenas tend to stay within their territories but in the Serengeti, where large herds of ungulates migrate long distances, the hyenas will commute to the migrating herds, often passing through the territories of other clans where they are tolerated when it is apparent they are not hunting. Hyenas are very aware of any kill made within their territory and immediately come running when cheetahs, lions, leopards or any other hyenas make a kill. If the kill is made by their own clan, then dominant females immediately take over and the low-ranking individuals must wait their time. This can result in low-ranking individuals not getting access to kills they have made so it is often more profitable for the low-ranking individuals to hunt alone.
Hyenas clearly have a complex and tense matriarchal social life with interactions amongst clan members, neighboring clans and while only the spotted hyena amongst the 4 hyena species has a pseudo-penis, none of this really explains the evolution of the pseudo-penis. The very presence and shape of it means it is not physically easy to copulate and so the female can select who she lets mate with her. Some have suggested that it is a by-product of female-female aggression or siblicide whereby females and not males are identified as potential competitors in the clan and so they developed pseudo-penises to hide their sex. Field work has shown that giving birth with a pseudo-penis has its problems and can lead to death of the babies while on the other hand it appears to be useful in the complex greeting displays. Maybe there is no simple explanation, and this developed through selection for several characteristics. Either way it is a great subject for discussion when you are next in your Land Cruiser in the Mara and they are indeed interesting animals to watch.
