The hyenas (Hyaenidae) are a family of mammals from the order of carnivores (Carnivora) with four recent species that live in large parts of Africa and in western and southern Asia. The term hyena is often used to refer specifically to the largest and most populous species, the spotted hyena, which is frequently seen in animal films, primarily because of its rivalry with lions.
Hyenas are divided into two subfamilies. The three species of the first, the actual hyenas (Hyaeninae), are characterized by a strong bite: the spotted, the striped and the scraped hyena. The spotted hyena feeds primarily by active hunting, while the striped and pelagic hyenas are primarily scavengers. The monotypic second subfamily (Protelinae) is represented by the aardwolf, which feeds almost exclusively on the representatives of a termite genus, and whose molars are greatly reduced in size because of this. The main threat to the hyenas is hunting by humans.
Features
General conformation and coat
The head-torso length is 55-160 cm, the tail is relatively short with 20-40 cm. The shoulder height measures 45-81 cm, the front legs are longer and more powerfully built than the hind legs, which is the cause of the sloping back typical of all hyena species. Females of spotted hyenas, the largest species, are about 10% larger than males; there is no significant sexual dimorphism in size among the other species. Actual hyenas weigh 26-55 kg, with individual spotted hyenas reaching 86 kg; the aardwolf is by far the smallest and lightest species, weighing 8-14 kg. Hyenas have four toes on their fore and hind legs, except for the aardwolf, which has one more toe on each foreleg. The paws bear blunt, non-retractable claws.
The outer hairs are rough; with the exception of the spotted hyena, all species have a long dorsal mane extending from the ears to the tail. This mane can be erect, making the animal appear larger. Various shades of brown are evident in the coat of each species; the spotted hyena is spotted, the striped hyena and aardwolf are striped, and only the saddleback hyena is largely solid in color. The tail is bushy.
Females have one to three pairs of teats; males, unlike most other predators, lack the penis bone (baculum). Female spotted hyenas exhibit masculinization (“masculinization”) unique among mammals: The clitoris is enlarged, and the labia are closed to form a scrotum-like structure. This “mock penis” prevents mating without the consent of the female partner due to its location. Urination, mating, and parturition occur through the clitoris. Adolescent striped hyenas have bulges in the genital tract, but when fully grown, like the other two hyena species, they show no peculiarities in the construction of the sexual tract. Both sexes have a well-developed anal pouch from which a secretion is secreted that is used to mark territory.
Head and teeth
Diagnostic features of hyenas are found in the sphenoid bone, where the alisphenoid canal is absent, and in the bones of the middle ear region, where the endotympanic portion of the tympanic bladder is small, but the ectotympanic portion is inflated. In addition, the construction of the skull and teeth shows the greatest differences between the two subfamilies: the actual hyenas carry a bulky head on their powerful neck, and their snout is broadly built, whereas the head of the aardwolf is slender with a pointed snout.
The incisors of the hyenas are unspecialized, and the outer ones are larger than the others. The canine teeth are enlarged. The dentition of the actual hyenas is strong. The premolars are adapted to breaking bone and are enlarged, especially the third upper and third lower premolars. Their enamel has a complex structure, which prevents the teeth from breaking. The fourth upper premolar and the first lower molar are developed into fangs, as in all terrestrial predators; these teeth are blade-shaped and are used for cutting meat. The molars behind the fangs are reduced in size or absent altogether, leaving more space for the remaining molars: the premolars become wider, and the fangs are thus better protected from abrasion. The dental formula of the actual hyenas consists of 3/3 I, 1/1 C, 4/3 P, and 1/1 M, for a total of 34 teeth. The canines of the aardwolf are used exclusively for confrontation with conspecifics. The molars are regressed to small, widely spaced pins, the number of which may vary. The dental formula of the aardwolf is 3/3 I, 1/1 C, 3/1-2 P, and 1/1-2 M, for a total of 28-32 teeth.
Associated with the powerful dentition of the actual hyenas is a strong masticatory musculature; the temporalis muscle has a high crest at the point of attachment to the skull. The curved skull ensures a better conversion of the biting forces. Thanks to their exceptional jaw apparatus, spotted hyenas can develop biting forces of over 9 kN. They are able to break open the leg bones of giraffes, rhinos, and hippos that are over 7 cm in diameter. Adaptations of aardwolves to insect feeding consist of a broad palate with a wide, spatulate tongue covered with large, cone-shaped papillae.
The eyes of all hyenas are equipped with a tapetum lucidum, which allows good night vision. The ears are large and pointed, only in the spotted hyena are they rounded.
Distribution and habitat
Hyenas are native to much of Africa and western and southern Asia. In Africa, their range extends from the Atlas Mountains to South Africa, but they are absent from the pure desert areas of the Sahara and the Congo Basin. In Asia, they occur from Turkey and the Arabian Peninsula to Afghanistan and India. In the Pleistocene they were still widespread over large parts of Eurasia, but with Chasmaporthetes only one extinct genus is known, which also occurred in North America. In South America and Australia hyenas never existed.
In Asia, only one species, the striped hyena, occurs; it also inhabits northern Africa and thus has the northernmost range of all species. The spotted hyena is native to large parts of Africa south of the Sahara. The aardwolf lives in two separate areas in eastern and southern Africa, and the saddleback hyena inhabits a relatively small area in the south of the continent.
In general, hyenas tend to inhabit dry areas such as semi-deserts, savannahs, scrub steppes, and rocky mountainous lands; they are sometimes found in swamps and mountain forests. In the Ethiopian Highlands, they can be found as high as 4100 meters. However, they avoid pure sandy deserts as well as lowland rainforests. Hyenas are generally not very particular about their habitat, each of the four species occurring in several habitats. They have little shyness toward humans and occasionally stay near human settlements.
Way of life
Locomotion and activity times
Hyenas are digitigrade (toe-walkers) and stay exclusively on the ground. They cannot climb trees, but cope well with rocky terrain. They are very persistent animals: saddleback hyenas can travel more than 50 kilometers per night. All hyena species are largely nocturnal, only rarely going out to forage at dusk or, in the case of the spotted hyena, during the day on cloudy, rainy days. During the day, they sleep in burrows, hidden in brush, or on the ground. Thus, aardwolves often sleep in burrows taken from spring hares or other animals; sometimes hyenas make their own dens or make do with rock crevices. The spotted hyena does not use burrows except for raising young.
Social and territorial behavior
There is great diversity in social behavior. Spotted and pied hyenas live in groups called “clans.” In both species, groups of related females form the nucleus of a clan; in each case, the reproductive males are immigrants and are not related to the females. The social behavior of spotted hyenas is unique among predators: It resembles that of some Old World monkeys, such as baboons. In this species, clans can number up to 80 animals, which repeatedly split into smaller subgroups and reunite. Females are dominant and establish a strict hierarchy, with ranks being hereditary as mothers help their daughters attain the same position as them. Males are always subordinate to females and their group rank is higher the longer they belong to the group. In the pied hyenas, clans comprise 4-14 animals; variance in lifestyle exists depending on habitat. Only at high population densities do rank orders become established; males and females each have their own hierarchies, and both sexes are equal. In the striped hyena, the least studied species, several observations have been made: there are reports of solitary animals, of stable pair bonds, and of living together in groups. Presumably, the social behavior of this species is variable. Aardwolves form stable and long-lasting pair bonds when rearing young, though often the young were not fathered by the rearing male. Outside of the mating season, aardwolves exhibit little social behavior: They inhabit separate burrows and forage separately.
Hyenas are territorial animals, and territory size depends on the species and food supply: the territories of spotted hyenas in the prey-rich savannahs of East Africa measure about 20 km², while the territories of spotted and sable hyenas in the arid regions of southern Africa can be over 1000 km². The territories of aardwolves include about 3000 termite mounds and measure 1.5-4 km². The territories are marked with the strong smelling secretion of their anal pouches, which is whitish or yellowish in color. It is streaked on grass tufts or other objects in a semi-squatting position. While spotted hyenas often mark only territorial boundaries, the other species often place their scent marks inside the territory as well. In addition, all species create defecation pits near territorial boundaries or on frequently traveled routes, into which they defecate regularly. If a hyena encounters a non-group animal in its own territory, it tries to chase it away. With the exception of the spotted hyena, it erects its back mane and ruffles its tail hairs, making it appear larger. If this is of no use, she tries to chase the intruder away, these hunts end at the territorial border. Sometimes, however, there are fights, which are fought out with bites.
Communication
Since the territories are often huge and the animals often travel alone, olfactory communication, i.e. by means of smells, plays an important role. By means of the anal sac secretion, hyenas can recognize the sex, the reproductive status and the group membership of other hyenas. In actual hyenas, there is a special greeting ritual that members of the same group display when they come together: They sniff the nose or anal sac of the other animal or lick its back. In the case of spotted hyenas, the erect sexual organs – of both males and females – also play a role, which are sniffed or licked by the opposite animal.
Three of the four hyena species make only a few sounds. At best, they emit growls or screeches that are audible only over short distances. In contrast, the spotted hyena has a rich repertoire of vocal communication. The most commonly heard sound is a loud wuup, which can be heard over several kilometers and is used to make contact with other clan members. They also make grunting, crying and mooing sounds. Finally, the laughing or giggling sound is known, which is similar to human laughter; it signals that the animal accepts a lower rank.
Food
The four hyena species have occupied three distinct ecological niches in terms of diet. Spotted hyenas are active hunters, taking 60% to 95% of their prey themselves. They have a very high range of prey: the spectrum ranges from insects to elephants. However, they most often prey on larger ungulates, such as various antelopes – for example wildebeest and gazelles – or zebras. They hunt individually or in groups, depending on the prey. In doing so, they do not sneak up on their victims, but rely on their stamina. The form of food acquisition is also flexible: in addition to animals they hunt themselves, they also eat carrion or engage in kleptoparasitism, that is, they prey on other carnivores. This has been observed in jackals, cheetahs, leopards, African wild dogs, the other two actual hyenas, and lions.
Striped and pelagic hyenas are scavengers that also consume prey and plant material that they themselves have killed. A good part of their food is the carrion of larger vertebrates. Thanks to their powerful dentition, they can break even thick bones or turtle shells, and their efficient digestive system utilizes all body parts of an animal except hair, hooves and horns. The bacterial toxins contained in carrion do not affect their digestive or immune systems. Small mammals, birds and their eggs, and insects supplement their diet. It is unclear to what extent they eat even killed, larger prey. They are not good hunters, and most hunts fail. One exception is the sable hyenas of the Namibian coast, which hunt the resident young of the South African fur seals with great success.
Aardwolves eat almost exclusively termites, specializing in those of the genus Trinervitermes. The termites of this genus move in large groups on the earth’s surface at night and are licked up by aardwolves with their sticky tongues. The soldiers of these termites secrete a venom that is incompatible to numerous other insectivorous mammals, an exception being the aardvark, among others. Thanks to their insensitivity to this toxin, aardwolves largely avoid food competition with other animals.
Except for spotted hyenas that hunt in groups, hyenas usually forage individually, but several hyenas may come together to feed on larger prey or carcasses.
Hyenas do not need to drink; however, if water is available, they drink daily. Striped and saddleback hyenas meet their fluid needs with cucurbits and other plants.
Reproduction
The mating behavior of hyenas varies. Often promiscuous behavior prevails, that is, males and females reproduce with several partners each. In addition, polyandry, which is rare in mammals, is sometimes found in striped hyenas, meaning that a female has several male mating partners. The choice of mate is also variable: in striped hyenas, the nomadic males, which roam the territory of the clan without their own territory and solitary, are occasionally chosen as mates, possibly depending on the food supply. In aardwolves, in about 40% of procreations, the mate is not the partner with whom the female lives, but a more aggressive, stronger male from a neighboring territory. Males of Serengeti hyenas invest a lot of time in courtship. Gentle males have far more mating success than aggressive mates.
In most cases, reproduction is not seasonal, but can occur throughout the year. After a gestation period of about 90 to 110 days, the female gives birth to one to four young; in human care, there may be five. The degree of development of the newborns varies: while spotted hyenas already have the incisors and canine teeth of the deciduous dentition and their eyes are open at birth, striped and pied hyenas are less developed and their eyes are still closed. Newborn spotted hyenas are black in color, in the other species the fur coloration of the young resembles that of the adults, only instead of the dorsal mane a dark eel line is present.
Newborn hyenas spend their first weeks of life in a den. In spotted and sometimes in pied hyenas there are communal dens where the young of a clan grow up together. In aardwolves, males in the mother’s den guard offspring that are not, or are only partially, sired by them. This is, as far as is known, unique among mammals. After a few weeks, the young begin to explore the area outside the den. After a few months, they make their first foraging forays, initially accompanied by an adult, but later on their own. Young hyenas are suckled for a relatively long time, actual hyenas are not finally weaned until they are 12-16 months old. Sexual maturity occurs in the second or third year of life.
Hyenas and humans
It happens from time to time that hyenas enter livestock pastures and tear domestic animals. Spotted hyenas also occasionally kill humans, for example when they sleep unprotected in the open. There are reports of the striped hyena invading cemeteries, digging up and eating corpses. For these reasons, they are often pursued and hunted down with poison baits, firearms, or traps. Another reason for hunting is the healing powers attributed to various parts of the hyena’s body. The Tuareg fattened and ate striped hyenas at least until the 1940s, a practice also known from ancient Egypt. Other threats include the destruction of their habitat and the decline in prey due to human interference. Automobile traffic poses a threat. This danger is increased by the fact that hyenas often eat the carcasses of roadkill directly on the road, being careless of following vehicles.
With the exception of the aardwolf, populations of all hyena species are declining. For aardwolves, large-scale grazing tends to increase their preferred termite species, which has a positive effect on overall populations. Estimates of the total population of the various hyena species are 27,000-47,000 spotted hyenas, 5000-8000 sable hyenas, 5000-14,000 striped hyenas, and at least several thousand aardwolves. The IUCN lists the striped and pied hyena as “near threatened” and the aardwolf and spotted hyena as “not threatened” (least concern).
