Berenty 2006: Census of Propithecus verreauxi and Possible Evidence of Population Stress

We provide a survey of a folivorous lemur, Propithecus verreauxi (sifaka), in the Berenty Reserve, southern Madagascar. Higher densities of folivores in small patches occur in either high-quality food areas or in less disturbed refugia. The skewness of sex ratio, which in lemurs is often male-biased, can be critically exacerbated in population stress. We predicted that sifaka would show higher densities in areas where protein-rich food is abundant (prediction 1a) and in refugium areas (prediction 1b). Owing to increased competition by brown and ring-tailed lemurs and decreased food production by tamarind trees, we expected an extremely male-biased sex ratio (prediction 2). In November–December 2006, we counted and sexed 206 adult/subadult sifaka (49 groups) during daily walks in different forest zones (Ankoba secondary forest, to the north, Malaza gallery/scrub areas, and spiny forest, to the south). Sifaka may have decreased in the gallery forest to concentrate in Ankoba (in a sort of out-of-Malaza). The area contains protein-rich food (prediction 1a confirmed). Sifaka are proportionally more concentrated in the spiny area than in the degraded scrub forest (prediction 1b confirmed). The sex ratio is extremely male biased, possibly due to either high sifaka density, in Ankoba, or food availability reduction, in Malaza (prediction 2 confirmed). The sifaka population seems to be under stress: researchers need to resume demographic studies, interrupted in Berenty in the mid-1980s, to preserve in situ a species that is difficult to protect ex situ.