Spotted hyaenas in most parts of Africa give birth at any time of year to litters containing one or two cubs, although triplet litters are occasionally reported as well (Frank et al. 1991; Wahaj et al 2007). Females may give birth at the communal den or in a private birth den (East et al. 1989, Henschel and Skinner 1990b; White 2006). Mothers with low social status probably use birth dens away from the communal den to ensure that they can maintain continuous access to their cubs (White 2006). Mothers might also use isolated birth dens to ensure they become acquainted with their cubs before they transfer them to the communal den (East et al. 1989), although this seems unlikely as efficient mother-infant recognition occurs even when cubs are born in communal dens. As there are often several animals present at the communal den, cubs probably benefit from the vigilance of adults that can alert young to the presence of predators. Social interactions at the communal den between cubs and older members of the clan probably play an important role in helping cubs to integrate themselves into the dominance structure of the clan (Holekamp and Smale 1991, 1993, East et al. 1993; Drea et al. 1996). Cubs are maintained at the communal den for a period of 8 to 12 months; during this period the major source of food for cubs is milk provided solely by their mother (Hofer and East 1993c, Frank et al. 1995a).
Spotted hyaenas mating. Photos by Sofia. A Wahaj (right) and Jacob Bro-Jorgensen (left).
Females give birth through their penis-like clitoris. During parturition, the clitoris ruptures to permit the passage of the young, creating a large bleeding wound of several centimetres that can take weeks to heal. Age at first parturition varies substantially between two and five years (Frank et al. 1995a, Holekamp et al 1996; Hofer & East 1996). As all females reproduce and females rear their young together in the communal den, occupied dens may contain up to 30 young of different ages from up to 20 litters. Females usually nurse only their own cubs and reject approaches by other cubs. An exception to this rule was observed during a difficult period in the Kalahari when several mothers suckled offspring communally (Knight et al. 1992). Cubs are nursed for a prolonged period and not weaned until they are between 14 and 18 months of age (Hofer & East 1993c; Holekamp et al. 1996). The milk of the spotted hyaena has the highest protein content (mean 14.9%) recorded for any terrestrial carnivore, a fat content (mean 14.1%) exceeded only by that of palaearctic bears and the sea otter, and a higher gross energy density than the milk of most terrestrial carnivores (Hofer & East 1995a). Due to their milk’s high energy content and the long nursing period, spotted hyaenas have the highest energetic investment per litter of any carnivore (Oftedal & Gittleman 1989).
Reproductive success is related to dominance status in that high-ranking females have a higher reproductive success because they have a shorter interbirth interval and a better chance of rearing young successfully (Frank et al. 1995a; Holekamp et al. 1996; Hofer & East 2003). Sex ratios amongst adults are usually even or slightly female-biased (Mills 1990, Hofer & East 1993a, Frank et al. 1995a). Significant deviations in offspring sex ratios in singleton and twin litters are observed in some populations when cubs can first be sexed at the age of two to three months (Frank et al. 1991) and remain until weaning (Hofer and East 1997). Such deviations in the sex ratio from the expected distribution may be either due to changes in the sex ratio at conception (Holekamp & Smale 1995) or to sex-specific siblicide after birth (Hofer & East 1997).
Males disperse from their natal clan shortly after becoming reproductively mature, which is usually when they are two years old (Smale et al. 1997; Boydston et al. 2005), thus reproductively successful males are usually immigrants (Engh et al. 2001; Honer et al. 2007). Newly immigrant males join the male dominance hierarchy at the very bottom, beneath all females and natal males (Smale et al. 1997). Males increase in social status as their tenure in the clan increases (Frank 1986a, Mills 1990, East et al. 1993). Males invest considerable time in developing amicable relationships with clan females (East et al. 2003; Szykman et al. 2001; 2007). They do this in some cases by forming consortships and following females for periods of days or weeks (East et al. 2003; Szykman et al. 2007). Males that have devoted many years to developing relationships with females may be favoured by females and thus these males may father more cubs than immigrants with short-term tenure in a clan. Males attempting to mate with females in their natal clans fare very poorly compared to immigrants, so female preferences for immigrants may have promoted the evolution of natal dispersal by males n this species (Engh et al. 2002).