Bruce K. Johnson

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.

Temporospatial Distributions of Elk, Mule Deer, and Cattle: Resource Partitioning and Competitive Displacement

Abstract Rocky Mountain elk (Cervus elaphus nelsoni), Rocky Mountain mule deer (Odocoileus hemionus hemionus), and cattle frequently co-occur on landscapes in the northwestern United States. We hypothesized that niche overlap would be greatest between introduced cattle with either of the 2 native herbivores because coevolution between native elk and mule deer should have resulted in strong patterns of resource partitioning. We observed strong differences among species in use of space, especially elevation, steepness of slope, and use of logged forests. We used 2 temporal windows to examine both immediate (6 h) and long-term (7 days) effects of competition. We noted strong avoidance over a 6-h period among the 3 ungulates. That effect was weaker for the previous 7 days. Cattle were generalists with respect to habitat selection; the 2 native herbivores avoided areas used by cattle. Mule deer and elk avoided one another during the short temporal window (6 h), although spatial differences in habitat use often were not maintained over 7 days. Elk used lower elevations when cattle were absent and moved to higher elevations when cattle were present, indicating shifts in niche breadth and competitive displacement of elk by cattle. We demonstrated strong partitioning of resources among these 3 species, and presented evidence that competition likely has resulted in spatial displacement.

ELK DISTRIBUTION AND MODELING IN RELATION TO ROADS

We tested performance of 3 aspects of an elk (Cervus elaphus)-road density model that has been used extensively throughout western North America but has not been sufficiently validated. First, we tested the hypothesis that elk selection of habitats increases with increasing distance away from open roads. This forms the empirical basis for the model. Second, we compared the models predictions of relative elk habitat selection, or habitat effectiveness (HE), with observed values at varying levels of road density. And third, we examined the potentially confounding effects of different spatial patterns of roads on model predictions. We conducted our study during spring and summer, 1993-95, at the Starkey Experimental Forest and Range (Starkey), northeast Oregon. Selection ratios were calculated using >100,000 recorded locations of 89 radiocollared female elk, with locations mapped in relation to 0.1-km-wide distance bands away from open roads. Selection ratios increased with increasing distance from open roads, and varied between seasons, but not among years or individual animals. Linear regression models, using distance to open roads as a predictor, accounted for significant variation in selection ratios during spring and summer. Model predictions of HE, as measured by number of elk locations, corresponded only weakly, however, with observed values of HE. The contradictory results of these 2 analyses may be explained in part by our simulation results, which showed that potential reductions in elk HE vary strongly with the spatial pattern of roads, which is not measured by the elk-road density model. Our results suggest that (1) management of roads and related human activities during spring and summer should remain an important consideration for modeling and managing the elk resource; and (2) a spatially explicit road component is needed for elk habitat models.

DAILY AND SEASONAL MOVEMENTS AND HABITAT USE BY FEMALE ROCKY MOUNTAIN ELK AND MULE DEER

Abstract We examined movements and habitat use by female Rocky Mountain elk (Cervus elaphus) and mule deer (Odocoileus hemionus) using a large telemetry data set collected over 6 years at the Starkey Experimental Forest and Range in northeastern Oregon. The analysis contrasted hourly movements of elk and deer within the mosaic of vegetation and landforms at Starkey with daily and seasonal demands for forage, security, and other resources. Telemetry data from 15 April to 14 November, 1991–1996, were stratified into 30-day intervals and tested for daily cycles relative to habitat use and movements. Both elk and deer exhibited strong daily and seasonal patterns of movements and habitat use. Daily cycles were most pronounced during spring and autumn, were composed of crepuscular and intraday habitat transitions, and were more pronounced for elk than for deer. Although crepuscular transitions were accompanied by sharp increases in velocity, intraday changes in habitat were not. The results add considerable detail to previous studies that sampled only limited hours of the day and seasons of the year. The findings have significance for modeling efforts that attempt to replicate animal behavior on diverse landscapes.

Development of predictive models of nutritional condition for Rocky Mountain elk

Despite its preeminence as a game species in North America, little research exists to validate nutritional condition indices for Rocky Mountain elk (Cervus elaphus nelsonii). We developed and calibrated indices of nutritional condition for live and dead Rocky Mountain elk. Live-animal indices included 20 serum and 7 urine chemistry variables, a body-condition score (BCS), thickness of subcutaneous fat and selected muscles using ultrasonography, bioelectrical impedance analysis (BIA), and body mass. Dead-animal indices included femur and mandible marrow fat, 3 kidney fat indices, and 2 carcass-scoring methods. Forty-three captive-raised cows (1.5 to 7 years old) were randomly divided into 3 seasonal groups (Sep, Dec, and Mar). Within seasonal groups, elk were fed different diets to induce a wide range of condition; all were fed identical diets 7 days prior to sampling to eliminate short-term nutritional effects. Cows were euthanized and homogenized for chemical analysis of fat, protein, water, and ash content. Estimates of fat and gross energy (GE) were compared to each condition indicator using regression, with age and season as covariates. Relations between condition and thyroxine (T 4 ) and insulin-like growth factor (IGF-1) varied seasonally, and the relation between condition and mandible marrow fat varied among ages. Subcutaneous fat depth and BCS were most related to condition for live animals (r 2 ≥ 0.87, P < 0.001); carcass scores and kidney fat were most related to fat and GE for dead animals (r 2 ≥ 0.77, P < 0.001); and IGF-1 and T 4 were the only serum and urine indices at least moderately related to condition (r 2 ≥ 0.54, P < 0.001). Nearly all other serum and urine indices, bone marrow indices, and BIA were either poorly correlated with condition or exhibited highly nonlinear relations. These results identify several indices of condition useful for assessing nutritional condition of live or dead elk, and indicate a number of previously used techniques that correlate poorly with total body fat.

Resource selection and spatial separation of mule deer and elk during spring

Elk (Cerous elaphus) are sympatric with mule deer (Odocoileus hemionus) across large areas of western North America, where populations of mule deer have declined while elk populations increased. Insight into the interspecific relationships of elk and mule deer requires a clear understanding of the patterns of resource selection and spatial separation between the 2 species on shared range. Accordingly, we monitored distributions of mule deer and elk during spring, 1993-96 at the U.S. Forest Service Starkey Experimental Forest and Range (Starkey), in northeast Oregon. We recorded animal movements with an automated telemetry system (ATS) that provided locations of each radiocollared animal about every 1-4 hr, 24 hr/day. We linked animal locations to a geographic information system (GIS) of physical, vegetation, and human-activity variables identified from the literature as being important predictors of distributions of elk or mule deer, and used logistic regression to identify which variables best predicted resource selection. We validated models of resource selection by comparing predicted and observed selection in 2 study areas with 5 data sets of animal locations collected during spring, 1993-96. Of the 8 variables significant for either deer or elk, 4 variables were significant for 1 but not the other species, and coefficients (β) for 3 other variables differed in sign between the 2 species, demonstrating strong spatial separation between elk and mule deer. The resource selection function (RSF) for elk was a stronger predictor of mule deer selection than was the mule deer RSF as a predictor of elk selection. Mule deer distribution was inversely related to elk resource selection, but elk distribution was not related to mule deer resource selection. In 4 vegetation types that dominate Starkey, mule deer electivity index [(used - availability)/(used + availability)] declined as elk resource selection increased, while elk electivity index was independent of resource selection of mule deer. The dichotomy in resource selection between the 2 species, combined with the inverse relationship between mule deer locations and elk RSF, indicated that mule deer avoided areas used by elk. Removal experiments are needed under controlled conditions to explicitly test whether mule deer avoidance of elk results in decreased population or individual performance of deer.

Understanding Ungulate Herbivory—Episodic Disturbance Effects on Vegetation Dynamics: Knowledge Gaps and Management Needs

Abstract Herbivory by wild and domestic ungulates is a chronic disturbance that can have dramatic effects on vegetation dynamics. Herbivory effects, however, are not easily predicted under different combinations of episodic disturbance such as fire, timber harvest, drought, and insect defoliation. This lack of predictability poses a substantial obstacle to effective management of ungulate herbivory. Traditional models of vegetation transition in forested ecosystems have ignored the influences of ungulate herbivory, while research on effects of herbivory have typically excluded other disturbances. Of the 82 contemporary studies on ungulate herbivory we examined, only 15 (18%) considered the interactions of herbivory with episodic disturbances. Moreover, only 26 (32%) evaluated vegetation response to ungulate herbivory beyond the simplistic treatment levels of herbivory versus no herbivory. Only 31 (38%) used a repeated-measures design of sampling responses over 3 or more time periods. Finally, just 7 (9%) explicitly made inferences to large landscapes such as watersheds, which are often used for management planning. We contend that useful landscape research on herbivory must examine the interactions of ungulate grazing with other disturbance regimes at spatial extents of interest to forest and rangeland managers and under varying ungulate densities and species. We identify herbivory models that could accommodate such information for forested landscapes in western North America. Such models are essential for identifying knowledge gaps, designing future studies, and validating relations of ungulate herbivory on landscapes where episodic disturbances are common, such as those of western North America.

Neonatal mortality of elk driven by climate, predator phenology and predator community composition

1. Understanding the interaction among predators and between predation and climate is critical to understanding the mechanisms for compensatory mortality. We used data from 1999 radio-marked neonatal elk (Cervus elaphus) calves from 12 populations in the north-western United States to test for effects of predation on neonatal survival, and whether predation interacted with climate to render mortality compensatory. 2. Weibull survival models with a random effect for each population were fit as a function of the number of predator species in a community (3-5), seven indices of climatic variability, sex, birth date, birth weight, and all interactions between climate and predators. Cumulative incidence functions (CIF) were used to test whether the effects of individual species of predators were additive or compensatory. 3. Neonatal elk survival to 3 months declined following hotter previous summers and increased with higher May precipitation, especially in areas with wolves and/or grizzly bears. Mortality hazards were significantly lower in systems with only coyotes (Canis latrans), cougars (Puma concolor) and black bears (Ursus americanus) compared to higher mortality hazards experienced with gray wolves (Canis lupus) and grizzly bears (Ursus horribilis). 4. In systems with wolves and grizzly bears, mortality by cougars decreased, and predation by bears was the dominant cause of neonatal mortality. Only bear predation appeared additive and occurred earlier than other predators, which may render later mortality by other predators compensatory as calves age. Wolf predation was low and most likely a compensatory source of mortality for neonatal elk calves. 5. Functional redundancy and interspecific competition among predators may combine with the effects of climate on vulnerability to predation to drive compensatory mortality of neonatal elk calves. The exception was the evidence for additive bear predation. These results suggest that effects of predation by recovering wolves on neonatal elk survival, a contentious issue for management of elk populations, may be less important than the composition of the predator community. Future studies would benefit by synthesizing overwinter calf and adult-survival data sets, ideally from experimental studies, to test the roles of predation in annual compensatory and additive mortality of elk.

Effects of bull age on conception dates and pregnancy rates of cow elk

Productivity of cows in many Rocky Mountain elk (Cervus elaphus nelsoni) populations of northeast Oregon has declined over the last 30 years. Numbers of mature bulls declined concurrently, suggesting a potential link that accounts for declining productivity. We evaluated the influence of bull age on conception dates and pregnancy rates of cow elk within a 78-km 2 enclosure on the Starkey Experimental Forest and Range in northeast Oregon from 1989 to 1993. We allowed a single cohort of bulls to mature from 1 1/2 to 5 1/2 years and function as principal herd sires. Subsequent male offspring were reduced in numbers through hunting and trapping. We estimated conception dates, pregnancy rates, body condition, age, and lactation status of cows killed in December. Conception dates occurred earlier as bull age increased (P = 0.0001) and were significantly different between bulls ≤ 2 years and ≥ years of age. The rut became more synchronous and shortened from 71 days (n = 26) when breeding was by yearling bulls to 41 days (n = 33) when 5-year-old bulls were the principal sires. Pregnancy rates increased from 89 to 97% as bull age increased, but not significantly (P = 0.62). Cow body condition was highest (P = 0.004) in 1989 when breeding was by yearling bulls. To enhance herd productivity we recommend that elk hunting seasons be designed so that older bulls ( ≥ 3 yr) are retained in the population.

Experimental Design for Radiotelemetry Studies

Publisher Summary Design studies that use radiotelemetry require careful consideration of the goals of a project and the resources available to meet those goals. Success in meeting the research goals depends on thoughtful planning of field methods and ancillary data collection, selection of telemetry equipment appropriate to the study animal and budget, careful execution of the field protocols, and creative analysis of the data. Some of the most important design factors include consideration of the studys purpose; degree of experimental manipulation, controls, and replication; selection of an efficient yet unbiased sampling scheme; definition of the sample unit; calculation of sample size requirements; identification and removal of sources of bias; and clear specification of biological significance. This chapter emphasizes the need to integrate univariate metrics of animal choice, such as estimates of home range size and resource selection, with metrics for the demographic consequences of these choices, all of which can be generated from radiotelemetry. Radiotelemetry is an essential tool in modern studies of movement, migration, and dispersal of most vertebrates. Its use has dramatically increased the amount and detail of information available for estimating movements of larger animals, and provides extremely valuable additions to information from studies that use tagging, banding (ringing), and other forms of marking for smaller animals. In addition, radiotelemetry studies are an important complement to recent approaches that use genetic markers.