Group Composition and Monandry in Grizzled Langurs, Presbytis comata, on Java.

Area of Science:

• Primate Social Behavior
• Mammalian Ecology
• Conservation Biology

Background:

• Grizzled langurs (Presbytis comata) are sexually monomorphic.
• Reported social structures include 1-male/1-female or 1-male/multifemale groups.
• This suggests a potential monandrous mating system.

Purpose of the Study:

• Investigate the prevalence of 1-male/1-female groups.
• Determine the impact of habitat variation on social organization.
• Clarify the mating system of Presbytis comata across different elevations.

Main Methods:

• Field observations of grizzled langur groups.
• Data collection on group composition and size.
• Analysis of social organization in relation to habitat variables (altitude, forest fragment size, distance to edge).

Main Results:

• Presbytis comata observed in groups of 1-13 individuals from sea level to 2,565m.
• Predominantly 1-male/multifemale groups with offspring or all-male groups were recorded.
• Only 2 out of 55 groups were 1-male/1-female with offspring.
• Group size correlated negatively with altitude and forest fragment size, and positively with distance from forest edge.
• Higher altitudes showed fewer adult females, impacting group size.

Conclusions:

• 1-male/1-female groups are rare in grizzled langurs, contrary to initial assumptions.
• Habitat variation, particularly altitude, influences social organization.
• A monandrous system may occur at high altitudes, but lower elevations resemble other Presbytis langurs with multi-female groups.