Hyena

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, whose rivalry with lions is a popular theme in wildlife films.

Two subfamilies are distinguished among the hyenas. The three species of the first, the hyenas (Hyaeninae), are characterized by a strong bite: the spotted, the striped and the scabrous 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 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 at 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 that extends from the ears to the tail. This mane can be erected, making the animal appear larger. Different shades of brown are seen in the fur of each species, the spotted hyena is spotted, the striped hyena and the aardwolf are striped, 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 a masculinization ("Vermännlichung") unique among mammals: The clitoris is enlarged and the labia are closed, forming a scrotum-like structure. This "false penis" prevents mating without the consent of the female partner due to its position. 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 released that serves to mark territory.

Head and teeth

Diagnostic features of the 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 part of the tympanic bladder is small, but the ectotympanic part 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 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 carnivores; these teeth are blade-shaped and are used for cutting meat. The molars behind the fangs are reduced in size or absent altogether, thus leaving more room 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 serve exclusively for the 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.

Connected with the powerful dentition of the actual hyenas is a strong chewing musculature; the Musculus temporalis possesses a high ridge at the point of attachment to the skull. The curved skull ensures a better implementation 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, which are over 7 cm in diameter. Adaptations of aardwolves to insect food 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 they are rounded.

Skull of a spotted hyena: The domed skull and the strong molars are typical for the actual hyenas (Hyaeninae).

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. Hyenas never existed in South America and Australia.

In Asia, only one species, the striped hyena, occurs; it also inhabits northern Africa and thus has the northernmost distribution area 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 inhabit rather dry areas such as semi-deserts, savannahs, bush steppes and rocky mountainous areas; sometimes they can also be found in swamps and mountain forests. In the Ethiopian Highlands, they can be found as high as 4100 m. 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 towards humans and occasionally stay close to human settlements.