POPULATION STUDIES AND REPRODUCTION OF THE FERAL CATTLE (BOS-TAURUS) OF AMSTERDAM ISLAND, INDIAN-OCEAN

Amsterdam Island has supported a population of feral cattle since 1871. In 1987 a fence was erected across the island, and in 1988 and 1989 the whole population (n = 1059) living south of the fence (study area) was removed. Nine hundred and sixty one cults were analysed. Age of calves indicated that reproduction was seasonal, as 78% of births occurred within four months. Age al first calving ranged from 2-4 years. An estimation of the fertility (rate of conception) was 0.73 foetuses per cow per year. In the north part of the study area, 50-80 males have been killed for beef each year since 195 1. The effect of hunting was analysed and a zone where cattle had been free from human interference was defined. In this zone sex ratio was biased towards males (252 M : 201 F), owing to female biased mortality in individuals older than three years. The cause of the biased mortality might be a differential use of food resources between sexes.