Dispersal and Social Relationships

In their eastern Madagascar habitats, indris are dispersed into small and territorial groups due to mating behavior, possible inbreeding avoidance, and long-term development of infants. Indris live in groups of two adults, one male and female, along with their recent offspring (Pollock 1975). Pollock (1975) estimated that 3-5 groups of indris could be found per square kilometer in the wild, while Petter and Peyrieras (1974) observed only one group per square kilometer. Regardless of the exact spacing of indri groups, indris will disperse from their monogamous parents and siblings upon reaching reproductive maturity (Pollock 1975). Through this dispersion of young and reproductively active male and female indris, inbreeding is avoided within the original family group. Additionally, the monogamous lifestyle that young indris seek is helpful in the rearing of offspring which is an energy-costing and multiyear process.

Indris have developed an interesting social relationship in that females are apparently the dominant partner in monogamous pairs. Pollock (1979) observed that adult females will occupy a higher position in the forest canopy (where more opportunities for finding higher quality food exist) relative to the adult males in their groups. Females also receive a disproportionate amount of grooming from adult males, are displaced from their positions while feeding less than adult and subadult males, and often violently reject sexual advances from males (Pollock 1979). It has been hypothesized by Trivers (1972) that in monogamous primate species where male assistance in rearing the young is observed, such as the indri, it is critical for the female to prevent male desertion following mating. Thus, sexual selection could possibly be the cause for this unusual relationship. Females might have evolved to preferentially choose mates that would be less likely to assert any form of dominance.

Petter, J.J., and A. Peyrieras. 1974. A study of population density and home ranges of Indri indri in Madagascar. In Prosimian Biology, ed. R.D. Martin, G.A. Doyle, and A.C. Walker. London: Academic Press, pp. 39-48.

Pollock, J.I. 1975. “Field observations on Indri indri: a preliminary report.” In Lemur Biology, ed. I. Tattersall and R.W. Sussman. New York: Plenum Press, pp. 287- 311.

Pollock, J.I. 1979. “Female dominance in Indri indri.” Folia Primatologica 31:143- 159.

Trivers, R.L. 1972. Parental investment and sexual selection. In Sexual selection and the decent of man 1871-1971, ed. Campbell. London: Heinemann, pp. 136-179.