Robert A. Riggs

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

: 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 nutritions 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.

Nutrition-growth relations of elk calves during late summer and fall

We report nutrition-growth relations in juvenile Rocky Mountain elk (Cerous elaphus nelsoni) from mid-August through mid-November. Data were generated from 3, 18-day experimental trials in 1993 with 42 calves, and from general feeding and growth data collected in 1991 with 25 calves. Intake of digestible energy was linearly correlated with growth rate and accounted for 53-89% of the variation in calf growth. Maximum daily digestible energy intake and growth rates were 368 kcal/kg BM 0.75 and 0.70 kg/day in late August and early September and 342 kcal/kg BM 0.75 and 0.33 kg/day in mid-November. Intake-specific growth rates declined after late September, suggesting a seasonal influence on growth-intake relations. We developed a deterministic model of growth to compare body mass dynamics over autumn of calves on an optimum diet (i.e., 3.3-2.95 kcal of digestible energy/g of forage) versus calves on diets available to free-ranging elk (2.66-1.86 kcal/g). Model projections indicated a 21% difference in body mass of the 2 groups by mid-December due to the lower concentration of digestible energy in diets of free-ranging calves. Our results confirm the importance of nutrition in late summer and fall for growth of elk calves, suggest a mechanism linking dietary quality during this time to winter survival, and demonstrate the importance of evaluating forage quality for reliable assessment of habitat quality on elk summer and autumn ranges.

Accuracy, Precision, and Observation Rates of Global Positioning System Telemetry Collars

Abstract We addressed concerns regarding performance of various Global Positioning System (GPS) collar configurations for describing habitat use by Rocky Mountain elk (Cervus elaphus) in rugged, forested terrain. We tested 8 GPS collars (Lotek Wireless, Newmarket, ON, Canada) in 4 different model and equipment configurations at 2 reference points (an open hilltop and a forested ravine) to determine habitat-specific differences in performance among collar configurations. We then placed individual collars at 60 additional points that were stratified randomly among 4 canopy-cover classes and 3 classes of available sky. All collars exhibited a locational bias of 4 m horizontally west and of 10 m vertically below a reference standard established by position-averaging with a handheld receiver (Garmin 12MAP) calibrated at National Geodetic Survey benchmarks. The GPS collar models that were programmed for longer satellite-acquisition times provided greater location precision than models that had been programmed for short acquisition times to preserve battery power. Canopy cover and available sky had a greater effect on collar location precision and observation rates than slope, slope position, aspect, conifer basal area, tree height, canopy depth, or elevation. Researchers should test collars at known reference points to confirm that location precision and rates of observation are adequate for their particular study objectives. Manufacturers of GPS collars should inform clients of their programming criteria for acquisition time so that customers can make informed decisions regarding trade-offs between precision of locations, data quantity, and battery life.

Economic assessment of ungulate herbivory in commercial forests of eastern Oregon and Washington, USA

Four forest stands in eastern Washington and Oregon, USA, containing exclosures to prevent or impede ungulate herbivory, were modeled to forecast timber yields and soil expectation values (SEVs) at harvest. Contrasts of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) growth and yield inside and outside exclosures show that ungulate herbivory may either promote or depress tree volume growth. Projected income from stands with more intensive stocking management and with inclusion of regulated livestock herbivory was higher than that of less intensively managed stands without livestock for scenarios with projected rising stumpage price levels for 2040. Under an assumption of future stumpage prices held constant at 1990 levels, the reverse was true. Ungulate herbivory plus planted stock and prescribed fire in site preparation provided the highest stand value at two sites. Sites without prescribed fire fared better when fenced to prevent livestock or big game herbivory. The results illustrate that ungulate herbivory alone is not the determinant factor of the economic yield of stands, but ungulate herbivory can have substantial impact on site productivity when used in conjunction with prescribed fire, stocking control, and species selection.