Randy T. Larsen

Negative effects of an exotic grass invasion on small-mammal communities.

Exotic invasive species can directly and indirectly influence natural ecological communities. Cheatgrass (Bromus tectorum) is non-native to the western United States and has invaded large areas of the Great Basin. Changes to the structure and composition of plant communities invaded by cheatgrass likely have effects at higher trophic levels. As a keystone guild in North American deserts, granivorous small mammals drive and maintain plant diversity. Our objective was to assess potential effects of invasion by cheatgrass on small-mammal communities. We sampled small-mammal and plant communities at 70 sites (Great Basin, Utah). We assessed abundance and diversity of the small-mammal community, diversity of the plant community, and the percentage of cheatgrass cover and shrub species. Abundance and diversity of the small-mammal community decreased with increasing abundance of cheatgrass. Similarly, cover of cheatgrass remained a significant predictor of small-mammal abundance even after accounting for the loss of the shrub layer and plant diversity, suggesting that there are direct and indirect effects of cheatgrass. The change in the small-mammal communities associated with invasion of cheatgrass likely has effects through higher and lower trophic levels and has the potential to cause major changes in ecosystem structure and function.

Chukar Watering Patterns and Water Site Selection

Abstract We evaluated chukar (Alectoris chukar) watering patterns as well as habitat variables influencing water site selection in western Utah. Motion-sensing cameras and chukar dropping counts were primary techniques to evaluate watering patterns. We took vegetative and other habitat measurements at each water source (n = 43) to discriminate use from nonuse sites using logistic regression. Chukars watered during daylight hours with a modal hour from 1200 hours to 1300 hours daylight savings time. Annual patterns suggest limited use of water sources from November to May with first observed visits occurring in June and last observed visits in October. Shrub canopy cover was the only variable to discriminate between site types (P < 0.01). Cross validation showed a predictive success rate of 84%. Significant differences were found between use and nonuse sites in terms of security cover (P < 0.01), but not total cover (P > 0.05). Chukars seem to have a loose shrub canopy threshold near 11% that is likely due to predation risk. Water sources meeting this threshold received use, whereas those not meeting this threshold did not. Increasing shrub canopy cover above 11% did not translate into increased water source use. Managers might want to consider annual patterns when setting hunt season timing and structure as well as judging sites for new water developments based on shrub canopy cover. More generally, these results suggest a behavioral constraint on the use of water sources as a function of predation risk—we should expect other species to demonstrate similar behavioral constraints. These constraints must be considered in any effort to determine benefits or impacts of water developments.

Daily and seasonal patterns of activity at pygmy rabbit burrows in Utah.

ABSTRACT. The pygmy rabbit (Brachylagus idahoensis) is a secretive, obligate sagebrush-steppe resident of the Intermountain West and is one of two rabbits in North America that digs its own burrows. Although the pygmy rabbit has a recorded home range of 0.21–67.9 ha in relatively high sagebrush cover (21%–36%), they spend much of their time within 30–100 m of a burrow system. Due to big sagebrush cover in preferred habitat and the secretive behavior of pygmy rabbits, it is often difficult to study this leporid through direct observation. We used remote cameras to document pygmy rabbit activity at burrow systems in south central Utah from 2006 to 2008. We analyzed photographs from remote cameras for daily and seasonal patterns of activity. Our results suggested that time of day and season were important influences on activity level, while year and site were less so. Pygmy rabbits were active during all time periods of the day, but the greatest activity occurred in the morning, except during winter. Numerous other species were recorded by remote cameras, including other leporids, birds, rodents, reptiles, and terrestrial predators. Remote cameras are a valuable tool in understanding pygmy rabbit behavior, in addition to confirming rabbit presence in areas of interest.

Chukar Seasonal Survival and Probable Causes of Mortality

Abstract Chukars (Alectoris chukar) have been introduced throughout the world. Despite this widespread distribution, limited information regarding seasonal survival, probable causes of mortality, and other basic life history characteristics is available to manage this harvested species. We estimated the probable cause of mortality for chukars with radiotransmitters by examining evidence at kill sites. We used model selection to evaluate influences of seasonal effects (fall raptor migration, peak migration, and reproductive period), demographic effects (age and sex), radio weight, and year on survival of chukars in western Utah, USA, by using a known-fate model in Program MARK and 2 years of telemetry data. We captured and randomly fitted 125 individual chukars with 2 different-sized radiotransmitters (97 F, 20 M, 8 sex undetermined). Model selection results showed our top 3 models accounted for 99% of Akaikes Information Criterion weight, and each one had seasonal and year effects. Two-week survival estimates were lower during peak raptor migration in both years and significantly (P < 0.05) so in year 2 (2-week S = 0.87, 95% CI = 0.77–0.94) compared with other year 2 intervals (2-week S > 0.91). Annual survival was lower in 2005 (S = 0.03, 95% CI = 0.01–0.09) compared with 2006 (S = 0.19, 95% CI = 0.12–0.31). We documented 95 deaths and classified 56% unknown, 33% avian predation, 8% hunter harvest, and 3% mammalian predation. Our research suggests that predation on chukars is substantial during the peak fall raptor migratory period and that the hunting take under current regulations is relatively small and likely compensatory.

Water Developments and Canids in Two North American Deserts: A Test of the Indirect Effect of Water Hypothesis

Anthropogenic modifications to landscapes intended to benefit wildlife may negatively influence wildlife communities. Anthropogenic provisioning of free water (water developments) to enhance abundance and distribution of wildlife is a common management practice in arid regions where water is limiting. Despite the long-term and widespread use of water developments, little is known about how they influence native species. Water developments may negatively influence arid-adapted species (e.g., kit fox, Vulpes macrotis) by enabling water-dependent competitors (e.g., coyote, Canis latrans) to expand distribution in arid landscapes (i.e., indirect effect of water hypothesis). We tested the two predictions of the indirect effect of water hypothesis (i.e., coyotes will visit areas with free water more frequently and kit foxes will spatially and temporally avoid coyotes) and evaluated relative use of free water by canids in the Great Basin and Mojave Deserts from 2010 to 2012. We established scent stations in areas with (wet) and without (dry) free water and monitored visitation by canids to these sites and visitation to water sources using infrared-triggered cameras. There was no difference in the proportions of visits to scent stations in wet or dry areas by coyotes or kit foxes at either study area. We did not detect spatial (no negative correlation between visits to scent stations) or temporal (no difference between times when stations were visited) segregation between coyotes and kit foxes. Visitation to water sources was not different for coyotes between study areas, but kit foxes visited water sources more in Mojave than Great Basin. Our results did not support the indirect effect of water hypothesis in the Great Basin or Mojave Deserts for these two canids.

Greater Sage-Grouse and Range Management: Insights from a 25-Year Case Study in Utah and Wyoming☆

ABSTRACT Conservation of sagebrush (Artemisia spp.) systems is one of the most difficult and pressing concerns in western North America. Sagebrush obligates, such as greater sage-grouse (Centrocercus urophasianus; hereafter sagegrouse), have experienced population declines as sagebrush systems have degraded. Science-based management is crucial to improve certainty in range management practices. Although large-scale implementation of management regimens within an experimental design is difficult, long-term case studies provide opportunities to improve learning and develop and refine hypotheses. We used 25 years of data across three large landscapes in northern Utah and southwestern Wyoming to assess sage-grouse population change and corresponding land management differences in a case study design. Sage-grouse lek counts at our Deseret Land and Livestock (DLL) study site increased relative to surrounding populations in correspondence with the implementation of small-acreage sagebrush treatments designed to reduce shrub cover and increase herbaceous understory within a prescriptive grazing management framework. The higher lek counts were sustained for nearly 15 years. However, with continued sagebrush treatments and the onset of adverse winter conditions, DLL lek counts declined to levels consistent with surrounding areas. During summer, DLL sage-grouse broods used plots of small, treated sagebrush mosaics more than untreated reference sites. We hypothesize that sagebrush treatments on DLL increased availability of grasses and forbs to sagegrouse, similar to other studies, but that cumulative annual reductions in sagebrush may have reduced availability of sagebrush cover for sage-grouse seasonal needs at DLL, especially when extreme winter weather occurred.

Vigilance of kit foxes at water sources: A test of competing hypotheses for a solitary carnivore subject to predation

Animals that are potential prey do not respond equally to direct and indirect cues related to risk of predation. Based on differential responses to cues, three hypotheses have been proposed to explain spatial variation in vigilance behavior. The predator-vigilance hypothesis proposes that prey increase vigilance where there is evidence of predators. The visibility-vigilance hypothesis suggests that prey increase vigilance where visibility is obstructed. Alternatively, the refuge-vigilance hypothesis proposes that prey may perceive areas with low visibility (greater cover) as refuges and decrease vigilance. We evaluated support for these hypotheses using the kit fox (Vulpes macrotis), a solitary carnivore subject to intraguild predation, as a model. From 2010 to 2012, we used infrared-triggered cameras to record video of kit fox behavior at water sources in Utah, USA. The refuge-vigilance hypothesis explained more variation in vigilance behavior of kit foxes than the other two hypotheses (AICc model weight=0.37). Kit foxes were less vigilant at water sources with low overhead cover (refuge) obstructing visibility. Based on our results, the predator-vigilance and visibility-vigilance hypotheses may not be applicable to all species of prey. Solitary prey, unlike gregarious prey, may use areas with concealing cover to maximize resource acquisition and minimize vigilance.

Summer watering patterns of mule deer in the Great Basin Desert, USA: implications of differential use by individuals and the sexes for management of water resources.

Changes in the abundance and distribution of free water can negatively influence wildlife in arid regions. Free water is considered a limiting factor for mule deer (Odocoileus hemionus) in the Great Basin Desert. Consequently, a better understanding of differential use of water by individuals and the sexes could influence the conservation and management of mule deer and water resources in their habitats. We deployed remote cameras at all known water sources (13 wildlife water developments and 4 springs) on one mountain range in western Utah, USA, during summer from 2007 to 2011 to document frequency and timing of water use, number of water sources used by males and females, and to estimate population size from individually identified mule deer. Male and female mule deer used different water sources but visited that resource at similar frequencies. Individual mule deer used few water sources and exhibited high fidelity to that resource. Wildlife water developments were frequently used by both sexes. Our results highlight the differing use of water sources by sexes and individual mule deer. This information will help guide managers when siting and reprovisioning wildlife water developments meant to benefit mule deer and will contribute to the conservation and management of this species.

Long-Lasting Effects of Maternal Condition in Free-Ranging Cervids

Causes of phenotypic variation are fundamental to evolutionary ecology because they influence the traits acted upon by natural selection. One such cause of phenotypic variation is a maternal effect, which is the influence of the environment experienced by a female (and her corresponding phenotype) on the phenotype of her offspring (independent of the offspring’s genotype). While maternal effects are well documented, the longevity and fitness impact of these effects remains unclear because it is difficult to follow free-living individuals through their reproductive lifetimes. For long-lived species, it has been suggested that maternal effects are masked by environmental variables acting on offspring in years following the period of dependence. Our objective was to use indirect measures of maternal condition to determine if maternal effects have long-lasting influences on male offspring in two species of cervid. Because antlers are sexually selected, we used measures of antler size at time of death, 1.5–21.5 years after gestation to investigate maternal effects. We quantified antler size of 11,000 male elk and mule deer born throughout the intermountain western US (6 states) over nearly 30 years. Maternal condition during development was estimated indirectly using a suite of abiotic variables known to influence condition of cervids (i.e., winter severity, spring and summer temperature, and spring and summer precipitation). Antler size of male cervids was significantly associated with our indirect measure of maternal condition during gestation and lactation. Assuming the correctness of our indirect measure, our findings demonstrate that antler size is a sexually selected trait that is influenced–into adulthood–by maternal condition. This link emphasizes the importance of considering inherited environmental effects when interpreting population dynamics or examining reproductive success of long-lived organisms.

Looking Toward a Brighter Future for Lekking Grouse

The current range of lekking grouse, including greater sage-grouse (Centrocercus urophasianus), Gunnison sage-grouse (C. minimus), sharp-tailed grouse (Tympanuchus phasianellus), greater prairiechickens (T. cupido), and lesser prairie-chickens (T. pallidicinctus), covers much of the rangeland in the western and central United States, as well as portions of southwestern and south central Canada.1–4 All of these species have experienced generalized population declines within their range. Additionally, all lekking species (or subspecies of these species) in North America have been or are being petitioned for protection under the US Endangered Species Act. The legal status of lekking grouse has the potential to alter the management of rangeland resources, and management of those resources, in turn, infl uences the population status of lekking grouse. Although many publications have described in detail the decline and possible causes of decline in lekking grouse populations and associated habitats, only limited information is available to suggest habitat management practices that benefi t these species. This lack of information not only complicates matters for managers trying to increase habitat availability or quality, but encourages a reactive approach to management of lekking grouse that often emphasizes the depth of the problem rather than the nature of the solution. Given the lack of published information on “what works,” a symposium was held at the 2010 Society for Range Management meeting to highlight a selection of positive management and research advances in the conservation of lekking grouse species. The presentations from this symposium serve as the backbone for this article. Our effort is not comprehensive to all issues facing lekking grouse, but instead highlights successful or promising habitat management practices and strategies, as well as notable advances in our understanding of lekking grouse habitat. Because much of the information presented in the symposium originated from 1) after-the-fact case studies and 2) large-scale issues such as habitat dynamics and regional efforts to mobilize a diversity of stakeholders, across-the-board extrapolation to alternate locations might not be appropriate. The degree to which extrapolation is useful will depend on ecological and/or sociological contexts. However, management of lekking grouse is, if anything, a complex problem,5 and as such, case studies of large-scale management efforts can provide lessons learned and salient hypotheses for future research. It is our hope that this article will promote a continued dialogue between managers, landuser groups, and researchers on the conservation of lekking grouse species.