Janet L. Rachlow

Interannual variation in timing and synchrony of parturition in Dall's sheep

Timing and synchrony of parturition in Dalls sheep ( Ovis dalli ) were studied in Igloo Mountain, Denali National Park and Preserve, Alaska, from April through July 1988 and 1989. Median ± SD dates of birth were 18 May (±5.1 days) in 1988 and 27 May (±8.8 days) in 1989. Ninety percent of births occurred in a 27-day period in 1988 and in a 36-day period in 1989; interannual variation in timing and synchrony of parturition was pronounced. Mortality of young in this predator-rich environment, however, did not differ between years, suggesting climatic variability may contribute more than predation in constraining timing and synchrony of parturition in Dalls sheep.

Variability in Maternal Behavior by Dall's Sheep: Environmental Tracking or Adaptive Strategy?

Effects of environmental variation and timing of births on patterns of nursing and weaning behaviors were examined in Dalls sheep ( Ovis dalli dalli ) in central Alaska. Indices of plant productivity, growing season, and quality of diet (crude protein in feces) indicated that later plant phenology resulted in a shorter growing season in 1989. Timing of parturition was ca. 2 weeks later and less sychronous in 1989 than in 1988. Females responded to this delay of births, and to forage availability and quality, by nursing lambs for a greater total time following parturition, and by reducing total time spent nursing more rapidly in 1989. Maternal females exhibited behaviors associated with weaning more often during early lactation in 1989, when parturition was delayed. Patterns of maternal care did not correspond with indices of quality of diet, suggesting that these differences did not result from environmental tracking. At far northern latitudes, where the period in which to rear young is limited, females exhibited plasticity in patterns of maternal investment to compensate for variation in environmental conditions and timing of births. This variability in maternal care likely represents an adaptive strategy important even in highly predictable environments with only slight or occasional annual variation.

A Comparison of Two Modeling Approaches for Evaluating Wildlife–Habitat Relationships

Abstract Studies of resource selection form the basis for much of our understanding of wildlife habitat requirements, and resource selection functions (RSFs), which predict relative probability of use, have been proposed as a unifying concept for analysis and interpretation of wildlife habitat data. Logistic regression that contrasts used and available or unused resource units is one of the most common analyses for developing RSFs. Recently, resource utilization functions (RUFs) have been developed, which also predict probability of use. Unlike RSFs, however, RUFs are based on a continuous metric of space use summarized by a utilization distribution. Although both RSFs and RUFs predict space use, a direct comparison of these 2 modeling approaches is lacking. We compared performance of RSFs and RUFs by applying both approaches to location data for 75 Rocky Mountain elk (Cervus elaphus) and 39 mule deer (Odocoileus hemionus) collected at the Starkey Experimental Forest and Range in northeastern Oregon, USA. We evaluated differences in maps of predicted probability of use, relative ranking of habitat variables, and predictive power between the 2 models. For elk, 3 habitat variables were statistically significant (P < 0.05) in the RSF, whereas 7 variables were significant in the RUF. Maps of predicted probability of use differed substantially between the 2 models for elk, as did the relative ranking of habitat variables. For mule deer, 4 variables were significant in the RSF, whereas 6 were significant in the RUF, and maps of predicted probability of use were similar between models. In addition, distance to water was the top-ranked variable in both models for mule deer. Although space use by both species was predicted most accurately by the RSF based on cross-validation, differences in predictive power between models were more substantial for elk than mule deer. To maximize accuracy and utility of predictive wildlife–habitat models, managers must be aware of the relative strengths and weaknesses of different modeling techniques. We conclude that although RUFs represent a substantial advance in resource selection theory, techniques available for generating RUFs remain underdeveloped and, as a result, RUFs sometimes predict less accurately than models derived using more conventional techniques.

Spatio-Temporal Factors Shaping Diurnal Space Use by Pygmy Rabbits

Abstract Factors influencing patterns of space use by pygmy rabbits (Brachylagus idahoensis) are poorly understood. We studied diurnal space use by adult pygmy rabbits during multiple breeding and nonbreeding seasons at 3 sites in the Lemhi Valley, Idaho, USA, during 2004–2005. Pygmy rabbits used larger areas than predicted by allometric models and documented by some previous investigations. Sex and season strongly influenced space use by rabbits. Males used larger home ranges and core areas, more burrow systems, and more widely dispersed burrow systems than did female rabbits. We also documented significant differences among study sites in many movement parameters, which suggested that local resource distribution also might influence how pygmy rabbits use space. Our results indicated that pygmy rabbits use large areas and exhibit seasonal, sex, and site-specific variation in patterns of movement and space use. Therefore, larger areas of habitat may be needed to conserve pygmy rabbits to accommodate seasonal, regional, and potentially annual variation in resource availability and to maintain linkages among populations.

Effects of Season and Scale on Response of Elk and Mule Deer to Habitat Manipulation

Abstract Manipulation of forest habitat via mechanical thinning or prescribed fire has become increasingly common across western North America. Nevertheless, empirical research on effects of those activities on wildlife is limited, although prescribed fire in particular often is assumed to benefit large herbivores. We evaluated effects of season and spatial scale on response of Rocky Mountain elk (Cervus elaphus) and mule deer (Odocoileus hemionus) to experimental habitat manipulation at the Starkey Experimental Forest and Range in northeastern Oregon, USA. From 2001 to 2003, 26 densely stocked stands of true fir (Abies spp.) and Douglas-fir (Pseudotsuga menziesii) were thinned and burned whereas 27 similar stands were left untreated to serve as experimental controls. We used location data for elk and mule deer collected during spring (1 Apr–14 Jun) and summer (15 Jun–31 Aug) of 1999–2006 to compare use of treated and untreated stands and to model effects of environmental covariates on use of treated stands. In spring, elk selected burned stands and avoided control stands within the study area (second-order selection; large scale). Within home ranges (third-order selection; small scale), however, elk did not exhibit selection. In addition, selection of treatment stands by elk in spring was not strongly related to environmental covariates. Conversely, in summer elk selected control stands and either avoided or used burned stands proportional to their availability at the large scale; patterns of space use within home ranges were similar to those observed in spring. Use of treatment stands by elk in summer was related to topography, proximity to roads, stand size and shape, and presence of cattle, and a model of stand use explained 50% of variation in selection ratios. Patterns of stand use by mule deer did not change following habitat manipulation, and mule deer avoided or used all stand types proportional to their availability across seasons and scales. In systems similar to Starkey, manipulating forest habitat with prescribed fire might be of greater benefit to elk than mule deer where these species are sympatric, and thus maintaining a mixture of burned and unburned (late successional) habitat might provide better long-term foraging opportunities for both species than would burning a large proportion of a landscape.

Correlates of Male Mating Strategies in White Rhinos (Ceratotherium simum)

Territoriality is a common male reproductive strategy exhibited by polygynous ungulates, and mature male white rhinos ( Ceratotherium simum ) establish and defend year-round territories. One-third of adult males in the study population in Matobo National Park, Zimbabwe, delimited territories that occupied most available space; other adult males were relegated to following a nonterritorial strategy. Correlates of male territoriality included age and body size. Testosterone levels also differed significantly between territorial and nonterritorial males but were not related to age. Overall patterns of association with adult females did not differ with male status. However, territorial males spent significantly more time with females of higher reproductive value. These results suggest that reproductive consequences of the two male strategies may not be equal.

Natal Dispersal by Pygmy Rabbits (Brachylagus idahoensis)

Abstract Multiple factors likely influence natal dispersal behavior of juvenile mammals, which is typically male-biased. Because of their small body size and specific habitat requirements, pygmy rabbits (Brachylagus idahoensis) are expected to exhibit limited dispersal. We predicted that dispersal would be male-biased, that juveniles born later in the year would disperse farther, and that juveniles would be more likely to disperse away from areas of higher habitat saturation. We used radiotelemetry to study dispersal of 61 juvenile pygmy rabbits (31 males and 30 females) from shortly after emergence from natal burrows (April–July) to the beginning of the next breeding season (mid-March) during 2004–2006. Juveniles dispersed before 12 weeks of age, and typically completed dispersal movements within 1 week. Both sexes exhibited a high rate of dispersal (males = 90%; females = 80%); however, juvenile females settled more than 3 times farther from their natal areas than males. Median natal dispersal distances for males and females were 1.0 km (range = 0.03–6.5 km) and 2.9 km (range = 0.02–11.9 km), respectively. Dispersing juveniles crossed gravel roads and perennial streams; however, rabbits tended to initiate dispersal movements away from nearby streams. Mortality rates for male and female juvenile rabbits were 69.2% and 88.5%, respectively, and were highest during the first 2 months after emergence from the natal burrow. We found no evidence that date of emergence, body condition, or habitat saturation influenced dispersal frequency or distance in juvenile pygmy rabbits. Results indicate that pygmy rabbits are capable of dispersing long distances and suggest that their conservation will require land management at broader spatial extents.

Genetic diversity and population divergence in fragmented habitats: Conservation of Idaho ground squirrels

The Idaho ground squirrel, which consists of a northern (Spermophilus brunneus brunneus) and a southern subspecies (S. b. endemicus), has suffered from habitat loss and fragmentation, resulting in a reduction in both numbers and geographic range of the species. The northern Idaho ground squirrel (NIDGS) is listed as a threatened subspecies under the Endangered Species Act, and the southern Idaho ground squirrel (SIDGS) is a candidate. Because Idaho ground squirrel populations are small and often isolated, they are susceptible to inbreeding and loss of genetic diversity through drift. This research evaluates levels of genetic diversity and patterns of population divergence in both subspecies of Idaho ground squirrels. We hypothesized that NIDGS would exhibit lower genetic diversity and greater population divergence due to a longer period of population isolation relative to most SIDGS populations. Genetic diversity and divergence were quantified using 8 microsatellite loci. Contrary to expectations, SIDGS populations exhibited consistently lower levels of microsatellite diversity. Additionally, NIDGS exhibited only modest divergence among populations, while divergence levels among SIDGS populations were highly varied. Preliminary evaluations of mitochondrial DNA diversity and structure revealed lower diversity in NIDGS and some differences in gene flow that warrant further study. Based on our results, we suggest different management strategies for the two subspecies. Habitat restoration appears to be the most desirable conservation strategy for NIDGS populations. In contrast, low genetic diversity observed in SIDGS may warrant supplementation of isolated populations through translocations or captive breeding to mitigate further loss of genetic variability.

Prioritizing Habitat for Surveys of an Uncommon Mammal: A Modeling Approach Applied to Pygmy Rabbits

Abstract Determining occurrence and distribution is an essential 1st step in conservation planning for rare species. Spatial habitat models can be used to increase efficiency of field surveys and to improve understanding about factors influencing animal distributions. We used a modeling approach to identify and prioritize potential habitat for survey efforts for an uncommon mammal, the pygmy rabbit (Brachylagus idahoensis), for which detailed habitat data are limited. A base map of potential habitat in Idaho was defined using vegetation type and soil depth data. Documented locations (n = 164) were used to evaluate additional habitat variables to prioritize the potential habitat for surveys. We conducted field surveys to evaluate the predicted habitat attributes and document presence or absence of the species. Newly confirmed occurrences (n = 112) and absences (n = 139) were used to assess accuracy in predicting habitat priority ratings. Overall model accuracy was 65%. Eighty-four percent of the new occurrences were located in the 2 highest priority ranks, and <0.4% were located in the 2 lowest priority ranks. We offer several examples of how survey results can be used to improve the habitat model and increase efficiency of future survey efforts.

REINTRODUCTION AND GENETIC STRUCTURE: ROCKY MOUNTAIN ELK IN YELLOWSTONE AND THE WESTERN STATES

Abstract Translocation is a common tool for restoring wildlife populations; however, potential genetic consequences include reduced levels of diversity within and increased divergence among populations. Elk (Cervus elaphus) were extirpated across much of North America by the early 20th century, but subsequent translocation programs restored the species to much of its historic range. The effects of these reintroductions on current patterns of genetic diversity in the western United States are largely unknown. We predicted that populations initiated with few founders and those experiencing slow postreintroduction growth would exhibit lower levels of diversity than other reintroduced populations. We used 12 microsatellite markers to examine patterns of genetic variability across 5 reintroduced populations of elk and 2 source herds from the Greater Yellowstone Ecosystem. The northern and southern Yellowstone source herds, which migrate to wintering areas separated by more than 260 km, exhibited similar levels of genetic diversity and high levels of gene flow, identified through both direct (i.e., assignment tests) and indirect measures. Levels of genetic diversity also were relatively high in all populations (unbiased heterozygosity, HE = 0.51–0.60; allelic richness based on a sample size of 21, AR21 = 3.3–4.0) and did not differ significantly between source and reintroduced populations or among reintroduced populations. We observed low to moderate levels of differentiation (Weir and Cockerhams FST statistic, θ = 0.01–0.08) and small genetic distances (Neis standard genetic distance, DS = 0.02–0.11) between populations. The relatively high levels of genetic diversity and low differentiation observed among our sampled populations are in stark contrast to observations of low diversity and high differentiation among isolated reintroduced populations of elk in the eastern United States. These results suggest that gene flow that includes other elk populations in the western United States may aid in preserving genetic diversity and limiting genetic divergence.