Population studies and reproduction of the feral cattle (Bos taurus) of Amsterdam Island, Indian Ocean

Abstract

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 culls were analysed. Age of calves indicated that reproduction was seasonal, as 78% of births occurred within four months. Age at 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 1951. 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.