Factors Affecting Pregnancy in Free-ranging Elk, <em>Cervus elaphus nelsoni</em>, in Michigan

Abstract

Uncertainty exists as to which factors are most closely related to probability of pregnancy in Elk (Cervus elaphus), which thresholds are key for managers who want to assess the potential productivity of free-ranging Elk herds, and whether these thresholds vary among populations. We examined relationships among pregnancy, age, and mass for 513 harvested freeranging Elk in Michigan, and compared relationships with other published models and with thresholds derived from other free-ranging and penned populations to see if relationships were consistent among populations. Pregnancy rates varied (χ 2 2 = 136.3; P < 0.0001) among yearling (0.30), prime-aged (2.5-11.5-year-olds; 0.88), and old (> 12.5-year-olds; 0.60) cows. Probability of pregnancy in adult cows was related to mass (χ 2 = 7.4; P = 0.006), age (χ 2 = 12.6; P = 0.0004) and age class (χ 2 = 16.4; P < 0.0001), but not to lactation status (χ 2 = 0.4; P = 0.515); pregnancy was also positively related (χ 2 = 15.8; P < 0.0001) to mass in yearlings. Probability of pregnancy increased 1.02× and 1.04× for each 1 kg increase in body mass of adult and yearling cows, respectively, and prime-aged cows were 4.9× more likely to conceive than old cows. Compared to thresholds derived primarily from penned or farmed Elk, both adult and yearling free-ranging Elk in Michigan and elsewhere were able to achieve higher levels of pregnancy at lower body mass. Thresholds also varied among free-ranging Elk populations. Given variation among populations, managers should calibrate mass-pregnancy relationships for their respective populations to determine whether condition is potentially limiting pregnancy in their populations.

Regional and seasonal patterns of nutritional condition and reproduction in elk

“…Our data were similar to body mass for yearlings reported by Dean et al (1976) during early-winter ( x ¼ 162 kg) on feed grounds in western Wyoming and for 261 yearlings sampled during early-to mid-winter in the 1990s and 2000s at Starkey Experimental Station in northeast Oregon ( x ¼ 158 kg; M. Wisdom, United States Forest Service, unpublished data). Our estimates ( x ¼ 161.9 kg) were slightly lower than the average late autumn body mass reported for yearlings ( x ¼ 177 kg) in an increasing elk population in Michigan (Piasecke et al 2009) and lower than the 220 kg reported by Blood and Lovaas (1966) for 1 yearling female in Manitoba. Dale et al (2008) also concluded that winter weather and habitat had relatively little influence on growth and subsequent body size in caribou over the next summer, and indicated that growth rates during summer were limited by summer nutrition levels.…”

“…Estimates of nutritional condition of non‐lactating females also are confounded because no validated approach exists to identify lactation history over the previous 5–6 months before autumn capture without intensive and costly calf‐capture approaches. Therefore, females deemed non‐lactating at the time of capture are likely to be a heterogeneous group of animals in terms of their nutritional demands and expenditures over the previous months, and inferences from their condition data could be both ambiguous and potentially misleading (e.g., Piasecke et al ).…”

“…Our pregnancy rates fell within the ranges reported for yearlings in other herds (Greer 1968, Piasecke et al 2009) but were higher than would have been predicted from their body mass based on experiments in captive trials ( Fig. 16; Cook et al 2004a).…”

Nematode–coccidia parasite co-infections in African buffalo: Epidemiology and associations with host condition and pregnancy

“…In this study, we did not detect any effects of parasites, alone or in combination, on host pregnancy. While female ungulates in poor condition are less likely to conceive and carry pregnancies to term in some species ( VanRooyen, 1993; Piasecke et al, 2009 ), the effects of body condition and parasite infection on reproduction are very difficult to disentangle without experimental studies. Accordingly, other observational studies on fitness effects in ungulates have also failed to find strong evidence for a negative effect of parasites on reproductive fitness ( Irvine et al, 2006; Hughes et al, 2009 ).…”

Adjusting for body mass change in white‐tailed deer during hunting season

“…Age‐specific body mass of cervids is subject to temporal variation driven by fluctuations in absolute density and habitat quality, and valuable as part of a suite of herd performance metrics (Adams and Pekins , Morellet et al , Piasecke et al ). Body mass has been shown to respond to herd productivity (Gaillard et al , Schwartz and Hundertmark , Stewart et al ), juvenile survival (Loison et al , Unsworth et al , Cook et al ), and relative density (Keyser et al ).…”