Body reserves and pregnancy rates of introduced red deer in Patagonia (Argentina) after a period of drought

Abstract

Red deer (Cervus elaphus) were introduced to Patagonia in the 1920 ́s and have reached high densities in certain areas of the foreststeppe ecotone. Severe drought conditions during summer/autumn of 1999 were suspected to have an impact on reproduction of red deer. Necropsies of 50 adult females revealed a pregnancy rate of only 56% as compared to 98% in 19921998 or 100% in 19961997 in other population. The age distribution of pregnant females reflected the importance of not having been pregnant during the previous cycle. The primiparous 2 year-old females had a 77% pregnancy rate, whereas none of the lactating females were pregnant. Normally, a higher reproductive success occurs for middle age classes, thereby reducing the chances of becoming pregnant during stress periods which was reflected in this study in the age distribution of non-pregnant females. However, chest girths (as an index of body size) were not different for pregnant and non-pregnant females. Body fat reserves were severely depleted in most animals irrespective of reproductive status. The calf-to-adult female ratio in the following autumn was 30% as compared to 58% in 19911992. The ratio in the other population was 28% in the following autumn, indicating that the effect of the drought was regional. The results suggest that these red deer populations occur at densities where they can easily become food-limited through a singular environmental phenomenon such as a drought period. Although the recruitment rate was drastically reduced through such food shortage, the effect might be of short duration as the drought terminates, and red deer may continue to exert intensive pressure on the flora causing subsequent damage if population densities are not lowered through continuous hunting or other control means.