Bioacoustics of Crocuta crocuta

Movements, Home range and Social organization. On average, Spotted Hyenas in Kenya move 928 m per hour when active, and typically travel over 12 km during each 24hour period, with males moving more than females. In Serengeti, daily movements may be much greater than this, as resident hyenas often commute 30-40 km in orderto feed on migratory herbivores. Spotted Hyenas live in social groups, called clans, which contain from ten to eighty members. Large clans contain multiple matrilines of related females and their offspring, as well as a number of adult immigrant males that are generally unrelated to one another. Small clans may contain only a single matriline and a single breeding male. Clan size appears to be determined by abundance of local prey animals: where these are plentiful, as on the prey-rich plains of eastern Africa, clans are typically very large, but in desert areas of southern Africa, clans may be tiny. Clans are fission-fusion societies. That is, all clan members know each other individually, occupy a common territory, and rear their cubs together at a communal den, yet they also spend much of their time alone or in small sub-groups. Spotted Hyena clans bear little resemblance to canid packs or Lion prides, but they are remarkably similar in their size, structure, and complexity to the societies of cercopithecine primates. Like troops of baboons and macaques, Hyena clans typically contain individuals from multiple overlapping generations, and clans are structured by clear linear dominance hierarchies in which an individual’s rank determinesits priority of access to food and other resources. In contrast to the situation characteristic of other hyaenids and most other mammals, female Spotted Hyenas are socially dominant to all adult immigrant males. Rank relationships among female clan-mates are usually stable for periods of many years. Average relatedness among females from different matrilines within a clan is extremely low. 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 typically nurse 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 long after weaning. Similar to female baboons, the social status of a female Hyena is determined not by hersize or fighting ability, but by her mother’s social rank. Indeed, the acquisition of social rank during early development 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 protractedjuvenile period. Young Hyenas initially direct their aggressive behaviors equally at higherand lower-ranking individuals. But this changes rapidly during the first year of life as cubs learn to direct aggression only at animals lower in rank than their own mother. When youngsters become involved in disputes with group-mates, the mother intervenes on their behalf against all individuals lower-ranking than herself. Interventions by high-ranking mothers are more frequent and more effective than those by lowranking females. In addition, like young baboons, Hyena cubs are often joined in fights by coalition partners who 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. Patterns of competition and 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, particularly their close kin, to acquire and defend both their social rank and such key resources as food and territory. Young Spotted Hyenas of both sexes “inherit” the social rank of their motherearly in life, and retain their maternal rank as long as they remain in the natal clan. However, whereas females remain in their natal group throughouttheir lives, virtually all males disperse after puberty tojoin a new clan. When a male immigrates into a new group, he entersas the lowest-ranking Hyena in the dominance hierarchy; he behaves submissively to all Hyenas he encounters in the new territory, regardless of their size, fighting ability, or social rank. This results in a society in which adult females and their cubs are dominant to all adult male immigrants. A male Hyena loses his maternal social rank and its associated feeding privileges when he disperses. In their new clans, immigrant males sometimes invest a great deal of time and energy in developing amicable relationships with resident adult females, as males engaging in these amicable relationships may enjoy a high probability ofsiring cubs. Due to the female’s male-like genitalia, coercive sex is impossible, so female choice of mates is an important sexually selected force in this species. Mate choice by female Spotted Hyenas apparently drives males to disperse: females strongly prefer to mate with immigrants, and they appear to discriminate against adult natal males. Therefore, almost all offspring are sired by immigrant males. Immigrants queue for status within the male hierarchy of the new clan; the highest-ranking males are those that immigrated first into the clan. Malesrise in rank only when higherranking immigrants die or engage in secondary dispersal; roughly 40% of immigrants disperse again, although the potential benefits of secondary dispersal are unknown. Clan members defend group territories from neighboring Hyena groups. Territory size ranges from roughly 20 km ?® in East Africa to approximately 1500 km ? in the desert regions of southern Africa, and is negatively related to the density of available prey. Territorial behavior is exhibited by both sexes, although females engage in these activities more frequently than males. Intruders encountered within the territory are usually chased to the territory boundary. Border clashes with neighboring clans, called “clan wars”, are most commonly observed in habitats containing high densities of Hyenas, where intrusion pressure is most intense. Territorial behavioris rarely observed among Spotted Hyenas inhabiting the vast desert regions of southern Africa, where prey are sparse, clan size is small, intrusion pressure is low, and the home ranges of resident hyenas are enormous. In some parts of Africa, where densities of resident prey may be low but where migratory herbivores are available as prey, Spotted Hyenas are known to adopt patterns of space-use that differ strikingly from those seen in areas with year-round resident prey. Specifically, Spotted Hyenas may frequently commute long distances from their defended territory to herds of migratory prey. In the unusual “commuting system” exhibited by Spotted Hyenas in the Serengeti, individuals travel long distances north or south from their centrally-located clan territories in order to feed on migratory herbivores. Intruders are tolerated by territory residents when the intruders are merely passing through, although residents behave aggressively toward intruders found hunting or feeding. In Namibia , Spotted Hyenas defend territories that expand and contract in size seasonally, as migratory prey change locations. Territory boundaries are visited sporadically by multiple clan members performing border patrols, during which boundaries are marked by pasting. A strong-smelling, yellowish buttery secretion is deposited from the anal glands onto grass stalks during border patrols. Spotted Hyenas also commonly paste deep inside their territories, although the frequency with which this occurs is generally far less than in the other hyaenid species. The paste transmits information about an individual’s identity, sex, reproductive state, and clan membership. Young Hyenas engage in pasting behavior long before there is any paste in their anal sacs, suggesting that this behavior enables cubs to acquire group odors from sites where clan-mates had pasted earlier. Spotted Hyenas engage in ritualized greeting ceremonies in which two individuals stand parallel and face in opposite directions. Both individuals usually lift the hindleg nearest to the other and sniff or lick the anogenital region of the other. The unique aspect of their greetingsis the prominent role of the erect “penis” in animals of both sexes. This is used to signal submission. Greetings occur between hyenas of all ages and both sexes, although greetings between adult females and adult males are uncommon and restricted to high-ranking males. Cubs can erect their penis or clitoris and engage in greeting ceremonies as early as four weeks after birth. Spotted Hyenas recognize their group mates based on visual cues, odors, and individually distinctive vocalizations. These animals are well known fortheirrich vocal repertoire. They emit deep groansto call their cubs out of dens, high-pitched whines to beg for food or milk, and cattle-like lowing sounds to bring group-mates to a common state of high arousal. The sound most frequently heard during the night throughout much of sub-Saharan Africa is the long-distance vocalization of the Spotted Hyena, called a whoop. This loud call can be heard over several kilometers. Whoopsclearly serve a variety of functions. They can be rallying calls to gather scattered clan members together to defend territory boundaries, food resources, the communal den, or clan-mates in danger. Mothers whoop to locate their wandering cubs, and hungry cubs whoop to call their mothers so they can nurse. Spotted Hyenas sometimes whoop to recruit hunting partners. Whoops are also used as a form of individual display, particularly by males of high rank. Adult males whoop more frequently than females, and high-ranking males whoop more often than lower ranking males. Finally, Spotted Hyenas are well known for their laugh or giggle, which sounds much like maniacal human laughter. This vocalization is a signal of submission. A submissive individual giggles to signal to another Hyena thatit accepts a lower status.