Date of this Version
The Prairie Naturalist 49:28–30; 2017
Reproductive parameters such as conception date, and therefore parturition date, influence offspring characteristics such as sex ratio and birth mass. For example, late-conceiving reindeer (Rangifer tarandus) produced more female than male offspring compared to those who conceived early (Holand et al. 2006). Females that conceive later and therefore give birth later also can produce lighter offspring compared to those who conceive early (Schwartz et al. 1994, Holand et al. 2006). Because birth mass is positively related to adult body mass (Michel et al. 2015), conception and parturition date likely affect adult phenotype. In turn, this may influence survival because heavy birth mass increases the probability of overwinter survival of ungulates at northern latitudes (Loison et al. 1999, Côté and Festa-Bianchet 2001).
Knowing parturition dates can help in managing wildlife populations. For example, mean parturition dates for a population can be used as an indicator of population health because high-density populations are generally above nutritional carrying capacity and, as a result of nutritional limitations, will likely display mean parturition dates later than other populations (e.g., white-tailed deer, Odocoileus virginianus; Demarais et al. 2000). Knowing when peak parturition occurs is important to management; however, currently there are no parturition date estimates available for ungulate species in North Dakota, USA. Reporting mean parturition dates for these species will serve as baseline information that wildlife managers can use for comparison to free-ranging populations. Wildlife managers also can derive estimates of mean conception dates from reported parturition dates, which allows for them to adjust hunting seasons to coincide with peak breeding. Adjusting hunting season structure may be desired as male movement generally increases during the breeding season (Webb et al. 2010).