Frequently asked questions about hyaenas
Q: How can the different species of hyaenas be distinguished from one another?
A: Due to the downward slope of the back and loping gallop, striped hyaenas are frequently mistaken for the spotted hyaena (Crocuta crocuta) when seen at night. In daylight, the spotted pelage of the larger hyaena clearly distinguishes the spotted hyaena from the striped hyaena (Hyaena hyaena). The relatively short, dart tail of the spotted hyaena contrasts with the longer, lighter-colored tail of the striped hyaena, and thus may be diagnostic at night. In silhouette, the short, rounded ears of the spotted hyaena also contrast with the long, pointed ears of the striped and brown hyaena (Parahyaena brunnea). In the day, the aardwolf (Proteles cristatus) is frequently confused with the striped hyaena. However, the large differences in body size between the two species is diagnostic, as is the relatively long, thin snout of the aardwolf. It is obvious from the shape of the head and neck that teh aardwolf is not built for eating carrion or cracking bones, as are its three extant relatives. The finer coat hairs of the aardwolf also appear glossier than the coarse coat of the striped hyaena. In East Africa, resident human populations rarely differentiate between the three Hyaenids found there. The brown hyaena is most similar in size and body shape to the striped hyaena, but the coloration of the pelage is quite different and the ranges of the two species do not overlap.
Q: Do hyaenas attack and kill livestock?
A: Spotted hyaenas do sometimes attack and kill livestock in rural parts of Africa, mainly targetting sheep and goats, but also occasionally attacking cattle, camels or donkeys. Brown and striped hyaenas feed mainly on carrion, rodents, hares, insects and fruits so they very seldom attack livestock, and aardwolves never do.
Q: What is a "laughing hyaena," and why does a hyena “laugh?”
Although three species in the family Hyaenidae do not emit any vocalizations that sound anything like laughter, spotted hyaenas often make a sound called a “giggle.” This vocalization sounds very much like high-pitched, hysterical human giggling, and the fact that spotted hyaenas emit this sound has prompted people to refer to them as “laughing hyaenas.” However, when a hyaena giggles, this actually means it is quite nervous about something, not that it thinks something is amusing (see cartoons below). A spotted hyaena most often giggles in response to aggression directed at it by another individual, or when the “laughing” animal has some food that another hyaena wants. Thus the human analogue to a hyaena giggling might be a worried person saying “Please leave me alone!”.
Q: Is it true that spotted hyaenas are the "Cain and Abel of the animal world," and that they routinely kill their siblings?
A: No. Whereas it is true that spotted hyaenas sometimes commit siblicide, it is false that they do this routinely, so it is inappropriate to consider them similar to Cain and Abel. Siblicide occurs when the death of a cub is caused by a litter mate (sibling). At birth spotted hyaena eyes are open and the teeth fully erupted - two characteristics which are rare amongst carnivores. Litter mates engage in aggressive interactions within minutes after birth (Frank et al. 1991), and this can result in obvious scarring of the subordinate littermate. These early fights quickly lead to the establishment of a dominance hierarchy between siblings (Golla 1993, Smale et al. 1995; Wahaj & Holekamp 2006) and allow the dominant cub to control access to maternal milk. Siblicide in the spotted hyaena is facultative in that it occurs only in some twin litters. Rather than functioning to routinely kill one's sibling, the purpose of the early fighting observed between hyaena littermates is to establish an unambiguous dominance relationship within the litter. A cub that manages to kill its sibling may obtain significant benefits if its mother is unable to support multiple cubs. Sometimes this happens because one of the mother's two teats is damaged in a fight, and she can therefore only nurse a single infant. Sometimes this happens when prey are so scarce that the mother can barely support herself, much less multiple cubs. Growth rates of singletons are higher than those of twins (Hofer and East 1993c), and dominant siblings grow faster than their subordinate littermates (Wahaj & Holekamp 2006). In some populations, cubs with a higher growth rate have a better chance of surviving to the age of independence at two years (Hofer & East 1993c), although in other populations cubs with surviving littermates are more likely to survive themselves to reproductive maturity than those whose siblings die at a young age (Wahaj et al 2007). Thus it appears that the relative costs & benefits of killing one's siblings vary with current socio-ecological conditions among members of this species.
Q: Why did females with such heavily ‘masculinized’ genitalia evolve in spotted hyenas?
A: No one yet knows the answer to this question, but a number of different hypotheses have been offered as explanations. Although most of these hypotheses can be ruled out, at least two are still in the running. First, if these ‘masculinized’ genitalia have an adaptive function, they might play an important role in post-copulatory choice by female hyenas regarding which sperm will fertilize their eggs. Females in the wild often mate with multiple males when they are in estrus, and the sperm from these competing males must therefore often occur together in the female’s reproductive tract. The ovaries of the female spotted hyena are comprised mainly of stromal cells, and they contain very little follicular tissue, so the female hyena may have few ova relative to those produced, stored and released by other mammalian carnivores. In addition to being rather long and convoluted, the female’s reproductive tract contains vaginal lumen that are full of blind alleys and dead ends (Cunha et al 2003, 2005), so perhaps only the highest-quality sperm manage to travel all the way up this strange obstacle course to reach the female’s ova.
A second hypothesis suggests that, instead of having an adaptive function, the female’s odd genitalia merely represent a side-effect of selection for other male-like traits in females such as large body size or enhanced aggressiveness. However, if this second hypothesis is correct, the physiological mechanisms mediating female ‘masculinization’ on which selection inadvertently acted must have been different from the traditional androgenic mechanisms that sometimes accidentally masculinize chromosomal females in most other species of mammals, including humans. Even when pregnant female spotted hyenas are treated throughout pregnancy with drugs that block the action of androgenic hormones on the fetus, each female offspring of these treated females nevertheless develops a full-size pseudopenis (Drea et al 1998). Furthermore, being born through a long, tube-like phallus is potentially risky for young hyenas as they may sometimes suffocate during parturition (Frank & Glickman 1994), so it seems unlikely that the female’s phallus could be adaptively neutral in light of this potential cost.
Q: How often do hyaenas attack or kill humans?
A: Although the paleoanthropological record from some parts of the world suggest members of the hyaena family (eg., Pachycrocuta)once commonly preyed on humans (eg., on Peking man in China), this is no longer true and attacks on humans in the modern world are rare. Each year a very small number of Africans are mauled or killed by spotted hyenas in rural areas, most frequently when sleeping unprotected in the bush or moving about in the bush near dawn or dusk. Occasionally a hyaena will contract rabies and attack in broad daylight. Occasionally spotted hyaenas have been known to enter tents and drag out a human from the interior, but only under two special circumstances: when the tent is left unzipped or when meat is also present inside the tent with the attacked person. Thousands of tourists sleep in tents every night without problems in African game parks that are densely populated by spotted hyaenas, so there is no need at all to worry about hyaenas breaking in. Striped and brown hyaenas and aardwolves are not known to attack humans.
Q: How do you sex a spotted hyaena?
A: The spotted hyaena has been considered a hermaphrodite in many cultures because the secondary sexual organs appear to be very similar in males and females. The female clitoris is of the same size and shape as the penis, can be erected and it is situated in exactly the same position as the penis is in a male. Through the clitoris runs the urogenital canal, with an exit in a narrow slit at the tip, similar to the penis. The similarity to the male is further enhanced by two swellings simulating a scrotum. These swellings are slightly smaller than a male's scrotum, but are similar in form and colour and are located where the male organs can be found. According to Frank, Glickman & Powch (1990), form and colour of the scrotum are different; in the female the scrotum has a bilobed appearance whereas the testes of the adult male create larger and more distinctly rounded bulges. The scrotum of the adult female has a denser covering of hair, which is usually light in colour than the male. There is no vagina as the outer labiae are fused. The phallus of a male spotted hyaena has a pointed tip and an obvious constriction immediatley above the glans whereas the pseudopenis of the female has a blunt tip and lacks the constriction apparent in the male's penis. Teats or udders are often visible just anterior to the hind legs of an adult female, and the adult female often has a rather 'baggy' appearance whereas males generally appear quite leggy and trim by comparison.
Q: Are the societies of spotted hyenas like those of other mammalian carnivores?
A: No. Other social carnivores, including wolves, meerkats, lions and wild dogs, live in small groups in which adult members of each sex tend to be closely related to each other, and in which multiple adults often participate in offspring care. By contrast, spotted hyenas live in social groups, called “clans,” that contain up to 90 individuals, including multiple unrelated adult males and multiple matrilineal kin groups of related females and their young. Average relatedness among females from different matrilines within a clan is extremely low, and no hyenas other than the mother participate in care of young.
Although hyena clans bear little resemblance to canid packs or lion prides, they are remarkably similar in their size, structure and complexity to the societies of such old-world primates as baboons and macaques (Holekamp et al. 2007). Like troops of these monkeys, hyena clans typically contain individuals from multiple overlapping generations, and clans are structured by clear linear dominance hierarchies in which an individual’s rank position determines its priority of access to resources. As with female baboons, the social status of a female hyena is determined, not by her size or fighting ability, but by her mothers’ social rank. Indeed, the acquisition of social rank during early development in hyenas occurs in a pattern identical to that seen in many monkey species, a pattern called “maternal rank inheritance” by primatologists even though no literal inheritance occurs involving genetic transfer of status from mother to offspring. Instead, in both hyenas and baboons, maternal rank “inheritance” involves a great deal of important social learning that occurs during a protracted juvenile period. Like most primates, spotted hyenas produce tiny litters at long intervals, and their offspring require an unusually long period of nutritional dependence on the mother. Young hyenas are typically dependent on their mothers for milk for well over a year, and because it takes them years to become proficient at hunting and feeding, their mothers continue to help them gain access to food at ungulate kills for many months or years after weaning. Males reach reproductive maturity at around two years of age, and most females start bearing young in their third or fourth year.
Young hyenas initially direct their aggressive behaviors equally at higher- and lower-ranking individuals. But this changes rapidly during the first year of life as cubs come to direct aggression only at animals lower-ranking than their own mother (Smale et al 1993; Holekamp & Smale 1993). When youngsters become involved in disputes with group-mates, the mother intervenes on their behalf against all individuals lower ranking than herself (Engh et al. 2000). Interventions by high-ranking mothers are more frequent and more effective than those by low-ranking females. In addition, like young baboons, hyena cubs are often joined in fights by coalition partners that may be either kin or unrelated animals. Along with maternal interventions, coalition formation functions importantly in rank acquisition. Thus the mechanisms by which youngsters acquire their social ranks are virtually identical in hyenas and old-world monkeys (Engh et al 2000). Patterns of competition & cooperation among spotted hyenas are also remarkably like those found in baboons. Although hyenas compete intensively for food, they also rely heavily on cooperative interactions with group-mates to acquire and defend both their social ranks and such key resources as food and territory.