ORIGINAL PAPER Sex ratio variation in harvested moose (Alces alces) calves: does it reflect population calf sex ratio or selective hunting? Torunn Moe & Erling J. Solberg & Ivar Herfindal & Bernt-Erik Sæther & Kari Bjørneraas & Morten Heim Received: 27 June 2008 / Revised: 25 August 2008 / Accepted: 2 September 2008 / Published online: 6 November 2008 # Springer-Verlag 2008 Abstract During the last 30 years, the proportion of males in the calf harvest of moose (Alces alces) in Norway has decreased, indicating a decline in proportions of males recruited to the autumn populations. At the same time, the percentages of exclusive calf hunting permits and of calves shot have increased. The change in calf sex ratio may thus simply be the result of hunter preferences for slightly larger (6.2% higher body mass) male calves combined with fewer opportunities for selective hunting due to increasing hunting quotas of calves. We examined this hypothesis by analyzing the variation in sex, number of siblings, carcass mass, date, and location of kill of 16,330 moose calves harvested during 1970–2004. In the presence of hunting selection for larger calves, we predicted larger proportions of male calves to be harvested in populations with large sexual size dimorphism among calves. Similarly, we expected more males to be harvested from twin than single litters because hunters then can more easily compare twins and select the larger calf, which is more often a male. Increasing proportions of single female calves were also expected to occur in the daily harvest as the accumulated number of harvested calves increased and the proportion of calves left in the population decreased. We found no positive relationship between the proportion of male calves and the level of sexual size dimorphism, no clear difference in sex ratio between harvested single and twin calves, and no increase in the proportion of single female calves as the accumulated number of calves in the harvest increased. This suggests that the spatiotemporal variation in the harvest calf sex ratio in Norway most likely reflects differences in population calf sex ratios prior to the hunting season and not varying degrees of hunting selectivity. Keywords Ungulate . Hunter selectivity . Harvest data . Norway Introduction Several theories have been proposed to explain the regula- tion of offspring sex ratio variation in animals (Fisher 1930; Trivers and Willard 1973; Clark 1978; Myers 1978; Williams 1979). Fisher (1930) was the first to describe the allocation of resources to male and female offspring by adaptive variation. He proposed that parents should invest equal amounts of resources to both sexes and thus produce an additional of the cheaper sex. The benefit of producing male or female offspring will then regulate itself at 1:1 if both sexes require similar investments. Most vertebrate populations seem to follow the predictions of Fisher by Eur J Wildl Res (2009) 55:217–226 DOI 10.1007/s10344-008-0223-6 Communicated by W. Lutz T. Moe Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway E. J. Solberg Norwegian Institute for Nature Research, Tungasletta 2, 7485 Trondheim, Norway I. Herfindal : B.-E. Sæther : K. Bjørneraas (*) Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway e-mail: Kari.Bjorneraas@bio.ntnu.no M. Heim Norwegian Institute for Nature Research, Tungasletta 2, 7485 Trondheim, Norway