Reproductive Parameters of Moose During Population Expansion in North Dakota

ABSTRACT: Understanding reproductive parameters of a population is vital to management, especially during periods of population fluctuation. Therefore, our objective was to provide the first estimates of reproductive parameters such as pregnancy rates, litter size, fecundity rates, conception dates, and fetal sex ratios for a moose (Alces alces) population in North Dakota, USA. Between 1978 and 1986, the North Dakota Game and Fish Department necropsied 54 hunter-killed cow moose which were all harvested after the rut (10 November to 12 December). Pregnancy rates for calves (n = 7), yearlings (1.5 years, n = 6), and adults (≥ 2.5 years, n = 41) were 0%, 100% and 95%, respectively. Mean conception date was 2 October. Overall, mean litter size was 1.76 fetuses, twinning rate was 73.3%, and mean fecundity was 1.66 fetuses and 0.85 female fetuses/cow. Fetal sex ratio did not differ from the expected 50:50 ratio, but the odds of producing at least one male calf increased with dam age, but not dam weight or litter size. This population displayed reproductive parameters consistent with an irruptive and expanding moose population.