Size-related changes in winter condition of female and male reindeer calves

Abstract

This study investigated how relationships between body size and back-fat depth develop in female and male reindeer (Rangifer tarandus tarandus) calves in winter. Back-fat depths did not differ between male and female calves, but depended more strongly on body size in female calves. Because no sex difference was found in the post-rut sample (October), differences were not attributed to male puberty and consequent sexual activity. Sex differences might be related to the fact that female calves feed more often than males from craters dug in the snow by their mother and that daughters of dominant mothers share feeding craters with their mother most often. In the last sample month, February, the fattest males were medium-sized, but mean back-fat depths did not differ between medium-sized and large calves. The decreasing trend in size dependence of fat reserves of male calves through the winter possibly weakens the link between maternal investment and reproductive success of sons.