Patterns of Infant Care in Wild Siamangs (Symphalangus syndactylus) in Southern Sumatra

Abstract

Parental care—parental behavior that is likely to increase offspring fitness (Clutton-Brock 1991)—is an important component of reproduction for many animals. Among mammals, internal gestation and lactation constrain females to be the more investing sex, particularly during the initial stages of a reproductive attempt (Clutton-Brock 1989). The costs and benefits of abandonment or neglect of offspring differ between the sexes for most mammal species due to this heavy early female investment. Therefore, the interaction betweenmale and female reproductive strategies in mammals has generally resulted in male strategies that prioritize mating effort over parental investment (Trivers 1972; Clutton-Brock 1989). Uniparental female care is universal in solitary mammals, and is the most common pattern in social mammals (Kleiman and Malcolm 1981; Clutton-Brock 1991). Nonetheless, biparental care does occur in a minority of mammal species. Biparental care is most common among carnivores, primates, and rodents, and is often associated with social monogamy or cooperative breeding (Kleiman and Malcolm 1981; Clutton-Brock 1991; Jennions and MacDonald 1994), although some male parental care has also been reported in species with other grouping and mating patterns (e.g., Borries et al. 1999; Buchan et al. 2003). In many species displaying biparental care, there is intraspecific variation in the quantity of care provided by males (Webb et al. 1999). Patterns of parental care may affect and be affected by grouping patterns and mating systems (Trivers 1972; Emlen and Oring 1977; Emlen 1995), remating opportunities (Smith 1995; Marlowe 1998), population densities (Kokko and Rankin 2006), and adult sex ratios (Burley and Calkins 1999; Burley and Johnson 2002). Variation in the quantity or quality of male care in biparental mammals has been shown to affect infant survivorship (Gubernick