EFFECTS OF SUMMER‐AUTUMN NUTRITION AND PARTURITION DATE ON REPRODUCTION AND SURVIVAL OF ELK

By J. Cook, B. Johnson, R. Cook, R. A. Riggs, T. DelCurto, L. Bryant, L. Irwin. Wildlife monographs, 2004

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: Recent declines in numbers and juvenile recruitment in many elk (Cervus elaphus) herds in the western U.S. has sparked interest in factors that may cause these declines. Inadequate nutrition or delayed parturition, the latter of which may be caused by inadequate numbers of mature bulls (i.e., highly skewed sex ratios), may have separate or synergistic effects on population dynamics and productivity. We evaluated the implications of late parturition and summer-autumn nutrition on reproduction and survival of Rocky Mountain elk (C. e. nelsoni) using a captive herd of 57 cow elk. We induced early (Sep) and late breeding (Oct) and 3 levels of summer-autumn nutrition on the cows. Food was offered ad libitum at 3 levels of digestible energy (DE): high = 2.9-3.0 kcal of DE/g of diets, medium = 2.6-3.0 kcal/g, and low = 2.3-3.0 kcal/g. Within these ranges, DE content was gradually reduced from late June through early November to mimic seasonal changes in the wild. During summer and autumn, we measured calf growth; body mass, nutritional condition, and breeding dynamics of cows; and growth and pregnancy of yearlings. We also measured carry-over (i.e., time-lag) responses including over-winter calf and cow survival and parturition date and birth mass, as functions of previous summer-autumn nutrition and previous parturition date. Between autumn 1995 and spring 1998, we conducted 2 years of parturition-date, summer-autumn nutrition experiments, 2 winters of calf survival experiments, and 1 winter of cow survival experiments. Early birth provided calves with more time to grow before onset of winter. This “head-start” advantage was maintained through late autumn, but its magnitude was diluted in some instances due to faster growth of some late-born calves. Body mass, body fat, and timing and probability of conception by cows in autumn were little influenced by parturition date the previous spring. Summer-autumn nutrition significantly affected calves and their mothers. Growth of calves in the low and medium nutrition groups ceased by mid-September and late October. By December, calves in the high nutrition group were 40% and 70% heavier than calves in the medium and low groups, respectively. Cows in the high nutrition group accumulated about 75% and 300% more fat than cows in the medium and low groups by mid-October. Eighty percent of cows in the low nutrition group failed to conceive, and those in the medium group bred 10–14 days later than cows in the high group. Summer-autumn nutrition of calves influenced their probability of becoming pregnant as yearlings. Probability of pregnancy approached 100% for those yearlings that had high summerautumn nutrition as calves and yearlings, despite near starvation their first winter of life. Winter survival of calves was related to their size at the onset of winter. Smaller calves lost more body mass daily than did large calves, and thus they survived fewer days through winter. Summer-autumn nutrition largely determined calf body size at the start of winter and, consequently, determined the proportion of winter survived. Survival of cows over winter was as related to body fat at the onset of winter as it was to nutrition during winter. Carry-over effects of summer-autumn nutrition and parturition date on birth characteristics the following spring were minor. We detected no significant carry-over effect of summer-autumn nutrition or autumn condition on birth mass, although reduced condition in autumn delayed subsequent parturition date. Extent of body fat depletion in cows during the winter-survival experiments in 1998 accounted for 45% of the variation in parturition date. Ninety percent depletion delayed parturition an average of 34 days. Delayed parturition, of a magnitude expected due to highly skewed sex ratios (3 weeks under extreme conditions), probably has only a weak influence on vital rates of free-ranging elk. In contrast, fat accretion and probability of pregnancy of cows, and growth and overwinter survival of calves, were sensitive to small (10–20%) differences in DE content of food. Digestible energy levels of our 2 lower nutrition levels reflect DE ranges reported for large ungulate herds during summer and autumn in western North America. Thus, our data suggest that limiting effects of summer-autumn nutrition on populations may be greater than often assumed, perhaps greater than those during winter in some ecosystems, and consequently indicate a need for greater understanding of nutrition's influence on population dynamics and how this influence varies across space and time. To enhance future research, we present animal- and vegetation-based guidelines for evaluating nutritional influences on elk populations.

Subfields: Ecology

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Citations in the corpus

Noninvasive unmanned aerial vehicle provides estimates of the energetic cost of reproduction in humpback whales (2016, background): “Animals in good body condition generally have larger energy stores and therefore display more resilience and higher survival than individuals in poorer condition (Gaillard et al. 2000, Cook et al. 2004, Clutton- Brock and Sheldon 2010).”
Effect of Enhanced Nutrition on Mule Deer Population Rate of Change (2009, background): “Multiple studies have found habitat quality on summer range to be a key limiting factor of ungulate body condition, fecundity, and survival (Julander et al. 1961, Gaillard et al. 2000, Cook et al. 2004).”
Green‐wave surfing increases fat gain in a migratory ungulate (2018, methodology): “…between body fat and pregnancy, whereby there are no associated increases in probability of pregnancy as body fat increases above ~ 12% (Cook et al. 2004), we took a conservative approach to incorporating predicted body fat values and also included uncertainty in the predicted…”
Moose summer and winter diets along a large scale gradient of forage availability in southern Norway (2010, background): “Numerous studies have found habitat quality on the summer range to be a major factor governing body growth and fecundity (see, e.g., Klein 1970; Gaillard et al. 2000; Cook et al. 2004).”
NUTRITIONAL CONDITION OF NORTHERN YELLOWSTONE ELK (2004, methodology): “Research with captive elk indicates several important thresholds of body fat relevant to survival and reproduction (Cook et al. 2004) and could provide some insight into the significance of the body fat levels that we documented.”
Behavioral Responses of North American Elk to Recreational Activity (2009, background): “Cook et al. (2004) suggested that if elk body fat was reduced below 9% as the animal enters winter, there is an increased probability of that individual not surviving winter.”
Life-History Characteristics of Mule Deer: Effects of Nutrition in a Variable Environment (2014, background): “A better understanding of seasonal patterns of nutritional condition and its relative influence on population dynamics would improve our knowledge of life-history strategies and population regulation of ungulates (Stephenson et al. 2002, Cook et al. 2004, Parker et al. 2009, Monteith et al. 2013).”
A MULTI-SCALE TEST OF THE FORAGE MATURATION HYPOTHESIS IN A PARTIALLY MIGRATORY UNGULATE POPULATION (2008, background): “Cook et al. (2004) showed that even when summer forage DMD was .55%, small increases of 5% were sufficient to significantly increase calf, yearling, and adult female weights, reduce pregnancy rates, reduce calf winter survival, and lead to important lagged effects on future reproduction and…”
Sex-specific behavioural responses of elk to spatial and temporal variation in the threat of wolf predation (2007, background): “Moreover, temporal variation in risk produced stronger antipredator responses in cows than in bulls (Fig. 3), as expected based on cows’ greater latitude to pay the associated foraging costs (Geist 2002; Hudson et al. 2002; Cook et al. 2004; this study, Fig. 2). Because our marrow data were not a ”