Structure sociale de la population de bovins sauvages de l’île Amsterdam, sud de l’Océan Indien

Abstract

A herd of about 1 600 feral cattle (Bos taurus) lives on Amsterdam Island (southern Indian Ocean) since 1871. A preliminary study of its population structure and social organization was carried out during a whole year (1985-1986), along 4 altitudinal transects of fixed width (200 m). Females may be pregnant at 11/2 year of age. Calving takes place throughout the year, with a peak at the end of November and a low from April to August. Most deaths occur in August and September, chiefly of malnutrition. The Amsterdam feral cattle population consists of 60 % of adults, and 10 % of suckling calves less than 3 months old. The sex ratio is equal at birth ; males temporarily predominate among 1 to 2-3 years old animals, but there are only 30 males left for 100 females among adults as a consequence, at least in part, of selective hunting. For most of the year, males and females live separately, the younger males remaining within the maternal groups. In mots cases males also live at higher altitudes than females, joining them only briefly during the rutting season.