Scott L. Findholt

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.

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.

Mitigating spatial differences in observation rate of automated telemetry systems

Wildlife ecologists are increasingly interested in determining spatial distributions and habitat use of ungulates from locations estimated from both conventional and automated telemetry systems (ATS). If the performance of an ATS causes spatial versus random variation in probability of obtaining an acceptable location (observation rate), analysis of habitat selection is potentially biased. We define observation rate as the percentage of acceptable locations (i.e., those that meet signal strength, signal-to-noise ratios, geometric dilution of precision criteria) of the total locations attempted. An ATS at the Starkey Experimental Forest and Range (Starkey) in Oregon tracks movements of elk (Cervus elaphus), mule deer (Odocoileus hemionus), and cattle. We detected localized variation in observation rate of stationary radiocollars in 1993. Subsequently, we devised a method to estimate observation rate at various spatial scales using animal location data over 4 years (1992-95 ; n = 907,156 location attempts) to determine if the variation was spatial or random. We formulated 5 variants of a general linear model to obtain estimates of spatial variation in observation rate. All 5 models assumed spatially correlated error terms estimated from isotropic semivariograms. Three models included environmental variables as covariates correlated with observation rate. Models then were compared based on mean error, coefficient of determination, and residual plots. Random variation accounted for 47-53%, and spatial variation accounted for 38-45% of the variation in observation rate. One model was selected to demonstrate application of the correction to mitigate spatial bias in observation rate. Our results demonstrate the utility of semivariograms to detect and quantify spatial variation in observation rate of animal locations determined from an ATS.

Linking habitat selection to fitness-related traits in herbivores: the role of the energy landscape

Animals may partially overcome environmental constraints on fitness by behaviorally adjusting their exposure to costs and supplies of energy. Few studies, however, have linked spatiotemporal variation in the energy landscape to behaviorally mediated measures of performance that ostensibly influence individual fitness. We hypothesized that strength of selection by North American elk (Cervus elaphus) for areas that reduced costs of thermoregulation and activity, and increased access to high-quality forage, would influence four energetically mediated traits related to fitness: birth mass of young, nutritional condition of adult females at the onset of winter, change in nutritional condition of females between spring and winter, and neonatal survival. We used a biophysical model to map spatiotemporally explicit costs of thermoregulation and activity experienced by elk in a heterogeneous landscape. We then combined model predictions with data on forage characteristics, animal locations, nutritional condition, and mass and survival of young to evaluate behaviorally mediated effects of the energy landscape on fitness-related traits. During spring, when high-quality forage was abundant, female elk that consistently selected low-cost areas before parturition gave birth to larger young than less-selective individuals, and birth mass had a strong, positive influence on probability of survival. As forage quality declined during autumn, however, lactating females that consistently selected the highest quality forage available accrued more fat and entered winter in better condition than less-selective individuals. Results of our study highlight the importance of understanding the dynamic nature of energy landscapes experienced by free-ranging animals.

Comparison of Bite-Count and Rumen Evacuation Techniques to Estimate Cattle Diet Quality

Abstract We conducted a study to compare the bite-count technique (BC) of estimating forage intake and synthesized diet quality to direct estimates of diet quantity and quality with the use of the rumen evacuation technique (RE). We used four rumen-fistulated steers to evaluate both techniques. Four enclosures in a mixed-conifer rangeland were used. Each enclosure contained two 0.25-ha paddocks that were either nonstocked or stocked by cattle to remove 32 ± 4% of standing crop. We recorded bite-count data during foraging bouts for each steer in each paddock, and then evacuated each rumen following each foraging bout during summer (August). Paddocks stocked prior to each 20-min trial had a reduced (P < 0.05) quantity of forage consumed regardless of technique. BC and RE gave similar (P > 0.10) results on diet quantity and digestibility. However, BC-derived estimates were lower (P < 0.05) for crude protein (CP), acid detergent fiber (ADF), ash, and neutral detergent fiber (NDF). In summary, although BC has the advantage of not requiring rumen-fistulated animals, it did not yield comparable results to RE under range conditions with dense and diverse vegetation. Therefore, investigators should calibrate bite-count technique against fistula technique to solve any accuracy problem in their specific experimental conditions whenever possible.