DEMOGRAPHY OF PROPITHECUS-VERREAUXI AT BEZA-MAHAFALY, MADAGASCAR - SEX-RATIO, SURVIVAL, AND FERTILITY, 1984-1988

Eighty-five sifakas (Propithecus verreauxi) have been captured, marked, released, and monitored between September 1984 and August 1988 at the Beza Mahafaly Special Reserve in southwest Madagascar. Estimates are presented of the age and sex structure of this population and of age-specific fertility and survival. Using data from this and other studies, it is shown that sifaka tertiary sex ratios do not depart significantly from 50:50, but that they do differ significantly from those of haplorhine primates, which have strongly female-biased tertiary sex ratios. Two demographic mechanisms that could give rise to this distinction are considered: 1) intermittently male-biased birth cohorts among sifakas and 2) different patterns of survivor-ship in haplorhines and sifakas.