James W. Unsworth

Mule deer survival in Colorado, Idaho, and Montana

We examined survival rates of mule deer (Odocoileus hemionus) fawns (1 Jan-31 May) and adult (≥1 vr old) females (1 Jun-31 May) from Colorado, Idaho and Montana to assess the influence of survival on population dynamics over a broad geographic area. Survival rates were estimated from 1,875 radiocollared fawns and 1.536 radiocollared adult female-vears. We found significant year-to-year differences in overwinter survival rates of fawns among states (P < 0.001), while annual survival rates of adult females showed less variation across vears (P < 0.256). Sampling distributions of survival rates by age class were modeled with the beta-binomial distribution (BBD) and not found different among states (ad F: P = 0.118; fawns: P = 0,856), The mean overwinter survival rate for fawns was 0.444 (SE = 0.033), with SD = 0.217 (SE = 0.019). The mean annual survival rate for adult females was 0.853 (SE = 0.011), wiht SD = 0.034 (SE = 0.014). All 3 states exhibited differences in body size of fawns at the start of winter across years, and body size was a predictor of overwinter survival (P < 0.001). Fawn sex ratios in December at time of capture were not different from 50;50 (P = 0.729). However, a sex differential in overwinter survival of fawns was observed (P = 0.002), but beta-binomial models of survival distributions were not different between sexes (P = 0.458). Frequencies of 3 categories of proximal causes of fawn mortality predation, winter malnatrution other) differed among states (X 2 4 = 41.24, P < 0.001 ). A deterministic model with a mean winter survival rate of 0.444 for fawns and an annual rate of 0.853 for adult females predicted December fawn:doe ratios would have to be at least 66: similar processes regulate these populations hence results from specific study areas are generally more applicable than commonly thought.

Elk Habitat Selection on the Clearwater National Forest, Idaho

Habitat management for bull and cow elk (Cervus elaphus nelsoni) may require different forest management standards because of likely sexual differences in distribution and habitat selection patterns. Current standards are based on the habitat use patterns of cow elk. Thus, we located 121 radiocollared elk (101 bulls, 20 cows) 4,527 times in the forested habitats of northcentral Idaho during 1986-90 to determine patterns of habitat selection. During winter, habitat selection patterns of ≥2-year-old and yearling bull elk were similar. but cow elk used more shrub habitats and less-open timber types. Cows typically used moderately steep areas on south-facing to west-facing aspects on the middle to lower elevational portions of the winter range. Bulls were more often found using small benches or ridgetop areas near the upper portion of hillsides. From spring through fall, elk shifted from using a high proportion of shrub and open timber habitats to use of timber habitats. In general, elk in areas with roads used habitats with greater canopy cover. This pattern was most pronounced for cow and ≥2-year-old bull elk. Yearling bulls tended to select habitats in proportion to availability, whereas cow and ≥2-year-old bull elk showed preference for open timber habitats during fall in non-roaded habitats and for timber habitat in areas with roads during summer and fall. Bulls tended to use higher proportions of lower slopes and stream bottoms than did cows during summer, and somewhat steeper areas during fall. Concern over forage production on summer range should be secondary to reducing disturbance and providing secure habitat during fall hunting seasons.

Demographic Response of Mule Deer to Experimental Reduction of Coyotes and Mountain Lions in Southeastern Idaho

ABSTRACT Manipulating predator populations is often posed as a solution to depressed ungulate populations. However, predator—prey dynamics are complex and the effect on prey populations is often an interaction of predator life history, climate, prey density, and habitat quality. The effect of predator removal on ungulate and, more specifically, mule deer (Odocoileus hemionus) populations has not been adequately investigated at a management scale. We tested the efficacy of removing coyotes (Cams latrans) and mountain lions (Puma concolor) for increasing survival and population growth rate of mule deer in southeastern Idaho, USA, during 1997–2003. We assigned 8 game management units (GMUs) to treatments under a 2 × 2 factorial design (treatments of coyote removal and lion removal) with 2 replicates of each treatment or reference area combination. We used methods typically available to wildlife managers to achieve predator removals and a combination of extensive and intensive monitoring in these 8 GMUs to test the hypothesis that predator removal increased vital rates and population growth rate of mule deer. We determined effects of predator removal on survival and causes of mortality in 2 intensive study sites, one with coyote and mountain lion removal and one without. We also considered the effects of other variables on survival including lagomorph abundance and climatic conditions. In these 2 intensive study areas, we monitored with radiotelemetry 250 neonates, 284 6-month-old fawns, and 521 adult females. At the extensive scale, we monitored mule deer population trend and December fawn ratios with helicopter surveys. Coyote removal decreased neonate mortality only when deer were apparently needed as alternate prey, thus removal was more effective when lagomorph populations were reduced. The best mortality model of mule deer captured at 6 months of age included summer precipitation, winter precipitation, fawn mass, and mountain lion removal. Over-winter mortality of adult female mule deer decreased with removal of mountain lions. Precipitation variables were included in most competing mortality models for all age classes of mule deer. Mountain lion removal increased fawn ratios and our models predicted fawn ratios would increase 6% at average removal rates (3.53/1,000 km2) and 27% at maximum removal rates (14.18/1,000 km). Across our extensive set of 8 GMUs, coyote removal had no effect on December fawn ratios. We also detected no strong effect of coyote or mountain lion removal alone on mule deer population trend; the best population-growth-rate model included previous years mountain lion removal and winter severity, yet explained only 27% of the variance in population growth rate. Winter severity in the current and previous winter was the most important influence on mule deer population growth. The lack of response in fawn ratio or mule deer abundance to coyote reduction at this extensive (landscape) scale suggests that decreased neonate mortality due to coyote removal is partially compensatory. Annual removal of coyotes was not an effective method to increase mule deer populations in Idaho because coyote removal increased radiocollared neonate fawn survival only under particular combinations of prey densities and weather conditions, and the increase did not result in population growth. Coyote-removal programs targeted in areas where mortality of mule deer fawns is known to be additive and coyote-removal conditions are successful may influence mule deer population vital rates but likely will not change direction of population trend. Although mountain lion removal increased mule-deer survival and fawn ratios, we were unable to demonstrate significant changes in population trend with mountain lion removal. In conclusion, benefits of predator removal appear to be marginal and short term in southeastern Idaho and likely will not appreciably change long-term dynamics of mule deer populations in the intermountain west.

Elk mortality in the Clearwater drainage of northcentral Idaho

Habitat condition and hunter density may affect mortality rates of elk (Cervus elaphus), and therefore, the amount of recreational opportunity offered hunters. Thus, we radio-monitored 121 elk in the forested habitats of northcentral Idaho during 1986-91 to determine cause-specific mortality. Sixty-nine deaths recorded during this period included: 43 recovered rifle kills, 8 rifle wounding losses, 4 archery wounding losses, 2 recovered archery kills, 3 poaching kills, and 9 other mortalities. Eighty-six percent of all elk deaths occurred during September and October and were associated with hunting. Annual survival rate of cow elk was 0.886 (SE = 0.094). Annual survival rate of bull elk was 0.600 (SE = 0.063)

MULE DEER SURVIVAL AMONG ADJACENT POPULATIONS IN SOUTHWEST IDAHO

Abstract We investigated survival and cause-specific mortality of mule deer (Odocoileus hemionus) on 3 distinct winter ranges in southwest Idaho from 1992 to 1997 to identify demographic variation and potential limiting factors based on a sample of 447 radiocollared deer. During winters 1995–1996 and 1996–1997, we modeled overwinter fawn mortality based on early winter mass, sex, activity, and habitat use variables. Annual survival rates of adult mule deer varied among the 3 adjacent study areas (χ22 = 10.93, P = 0.004). Overwinter deer survival also varied among study areas (χ22 = 8.00, P = 0.018), and the study area × year, study area × sex, and study area × age interactions were all significant (P ≤ 0.018). Overwinter survival differences among the study areas were not consistent over time or among sexes and ages of deer. Winter malnutrition was the main cause of mortality for both adults and fawns during the severe winter of 1992–1993, when overall survival was low. Excluding harvest, predation was the major proximate cause of deer mortality during 1993–97 when overall survival was higher. The probability of winter fawn mortality increased with lower mass (χ21 = 7.38, P = 0.007), being male (χ21 = 5.61, P = 0.018), smaller group sizes (χ21 = 3.62, P = 0.057), and using steeper slopes (χ21 = 3.05, P = 0.081). Smaller group sizes and use of steep slopes corresponded to conditions where predators were more successful. Our findings suggest that coyote (Canis latrans) predation was largely compensatory whereas mountain lion (Puma concolor) predation was apparently independent of animal condition and dependent more on deer habitat use. Early winter fawn mass was a better predictor of overwinter fawn survival than a suite of winter resource use variables, lending further support for use of fawn mass to predict winters where fawn mortality may be high. No single population in this study could be used to make reliable inferences regarding deer survival in the other populations. Survival rate measurements should be used cautiously to make inferences in populations where survival has not been directly measured.

Estimation of wildlife population ratios incorporating survey design and visibility bias

Age and sex ratio statistics are often a key component of the evaluation and management of wildlife populations. These statistics are determined from counts of animals that are commonly plagued by errors associated with either survey design or visibility bias. We present age and sex ratio estimators that incorporate both these sources of error and include the typical situation that animals are sampled in groups. Aerial surveys of elk (Cervus elaphus) in northcentral Idaho illustrate that differential visibility of age or sex classes can produce biased ratio estimates. Visibility models may be used to provide corrected estimates of ratios and their variability that incorporates errors due to sampling, visibility bias, and visibility estimation

How many mule deer are there? Challenges of credibility in Colorado

Abstract Conflict resolution between stakeholder groups and management agencies is a problem in wildlife management. We evaluated our success in resolving a conflict between sportsmen and the Colorado Division of Wildlife (CDOW). Sportsmen challenged the credibility of methods used to estimate numbers of mule deer (Odocoileus hemionus) in Colorado and demanded validating surveys to verify numbers of deer. Sportsmen, other interested wildlife stakeholders, and CDOW engaged in a conflict resolution process and designed and implemented an aerial survey to estimate numbers of deer in a specific population whose previous estimated size had been contested by sportsmen. We used helicopters to count mule deer on randomly selected sample units distributed on deer winter range in March 2001. Estimated population size was 6,782 ± 2,497 (90% CL) using stratified random sample estimators and 11,052 ± 3,503 (90% CL) when counts of deer were adjusted using the Idaho mule deer sightability model. Both aerial survey estimates supported computer-modeled population estimates of 7,000–7,300 deer that had been contested by sportsmen, and all estimates were greater than the sportsmen’s estimate of 1,750 deer, determined from their casual observations. After the survey, sportsmen did not accept survey estimates despite their involvement in the design, analysis, and interpretation of the validation survey. By failing to support results of a validation survey they had demanded, the credibility of sportsmen plummeted among other stakeholders, the Colorado Wildlife Commission, and outside public entities while credibility of CDOW managers rose. We contend that CDOW successfully met the challenges of sportsmen because the aerial-survey systems used to validate deer numbers were founded on credible science and applied within a resolution process that elicited trust from most stakeholders. We caution other agencies facing similar challenges to use tested methods that can withstand public scrutiny, allow ample time for planning and implementing, carefully assess technical and political risks associated with potential outcomes, and engage multiple stakeholders in planning efforts to gain the trust of participants. Cost of this resolution process was about

An approach for population assessment in the absence of abundance indices

100,000 US.

Female black bear habitat use in west-central Idaho

Population assessment models give managers insight into both the current status of a given population and how that population may respond to management measures. Nearly all of the techniques in both terrestrial and aquatic wildlife management require either an independent estimate of absolute abundance or an index that is consistently proportional to abundance. When neither of these exists, some information can still be mined from the changes in the sex and age ratios within the population over time. When harvesting is highly skewed toward a single sex or age class, the change in these ratios provides information about the exploitation rate and, when combined with absolute numbers removed, also provides information on absolute abundance. Traditional change-in-ratio techniques require independent estimates of other variables in order to be used in a predictive sense for open populations. This paper proposes a new method that combines the synthetic approach of fisheries stock assessment with the information contained in sex and age ratios to allow for the assessment of populations when no estimate of absolute abundance or reliable index of abundance exists. Although estimates of population parameters such as survival rates and fecundity are produced, the primary output of the estimation routine is the current population size and structure and the potential population sizes and structures that may result from future management options. The approach is validated using simulated data and is then applied to data for an elk population in north-central Idaho. Corresponding Editor: B. A. Maurer