Data on the body lengths (cm) of polar bears (Ursus maritimus), collec
ted as part of a long-term ecological study in the Hudson Bay region o
f Canada, were examined to test the hypothesis that growth early in li
fe influences adult body size. Data for 42 females and 30 males that w
ere captured as two-year-olds (2.6-2.9 years), after the period of mat
ernal care. and later recaptured as adults were analysed. On average,
females increased in length by 11.2% and males by 23.1% between captur
es. Relative adult body length was significantly correlated a with rel
ative length as a two-year-old in females but not in males. Thus, body
length attained by two-year-olds is a weaker determinant of adult bod
y length in males than in females. We suggest that, in comparison with
females. prolonged growth beyond the period of maternal care may pred
ispose the growth and eventual adult body size of male offspring to a
greater degree of environmentally mediated variation. Furthermore, whi
le data on maternal investment strategies in polar bears are lacking,
variation in the allocation of maternal resources to cubs, within and
among litters, may have a limited impact on the eventual adult body si
ze of any surviving male offspring.