Hyena societies

Although the family Hyaenidae contains only four living species, and is therefore one of the smallest among mammalian carnivores, it is remarkable for its ecological and social diversity, which surpasses that of much larger families such as canids and felids. The four extant hyena species represent the last remnants of a family that was once large and diverse. At the peak of hyaenid diversity in the Late Miocene (12–6 million years ago), at least 24 different hyena species concurrently roamed Eurasia and Africa [1]. Miocene hyaenids included not only robust, bone-cracking forms, but also many species that were dog-like in their appearance and feeding ecology. Since the Late Miocene, the family Hyaenidae has declined in species diversity and geographic range, such that hyenas now occur only in Africa and the Middle East. Nevertheless, modern hyenas occupy a vast range of habitat types, including deserts, montane forests and open savannas. Furthermore, they fill a surprisingly wide array of ecological niches, ranging from specialized insectivore to large predator. In parallel with this ecological variation, hyena societies also vary considerably, ranging from monogamous pairs to large, complex groups. The four living species in the family Hyaenidae (Figure 1) include the aardwolf (Proteles cristata), the striped hyena (Hyaena hyaena), the brown hyena (Parahyaena brunnea) and the spotted hyena (Crocuta crocuta). All of these animals are largely nocturnal, and all have hind legs that are somewhat shorter than their forelegs, giving their body profiles a sloping appearance (Figure 2). All of these animals communicate with one another by erecting their manes and tails, as well as through a rich repertoire of facial expressions [2]. They also rely heavily on chemical communication, and all hyenas mark their territories with deposits from anal scent glands. Here we will briefly describe the societies characteristic of the four living hyena species, consider the selection pressures that have shaped sociality in these animals, and inquire what we can learn by interspecific comparisons of social behavior among extant hyenas.