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For many species, behavioral modification is an effective strategy to mitigate negative effects of harsh and unpredictable environmental conditions. When behavioral modifications are not sufficient to mitigate extreme environmental conditions, intrinsic factors may be the primary determinant of survival. We investigated how movement behavior, and internal (i.e., nutrition and age) and external (i.e., food availability and snow depth) states affect survival over winter of a long‐lived and highly faithful species (mule deer; Odocoileus hemionus). We first tested whether animals changed their behavior during winter based on internal and external states; we subsequently investigated how behavior and state interacted to influence survival in the face of extraordinary winter conditions. Movement behavior changed minimally as a function of age and nutrition; yet, movement behavior affected survival—animals that exhibited more restricted movements were more likely to succumb to mortality overwinter than animals with less restricted movements. Additionally, nutrition and cumulative snow depth had a strong effect on survival: animals that were exposed to deep snow and began winter with low fat were much less likely to survive. Behavior was an effective tool in securing survival during mild or moderate winters, but nutrition ultimately underpinned survival during harsh winters.

Nutrition underpins survival and reproduction in animal populations; reliable nutritional biomarkers are therefore requisites to understanding environmental drivers of population dynamics. Biomarkers vary in scope of inference and sensitivity, making it important to know what and when to measure to properly quantify biological responses. We evaluated the repeatability of three nutritional biomarkers in a large, iteroparous mammal to evaluate the level of intrinsic and extrinsic contributions to those traits. During a long-term, individual-based study in a highly variable environment, we measured body fat, body mass, and lean mass of mule deer (Odocoileus hemionus) each autumn and spring. Lean mass was the most repeatable biomarker (0.72 autumn; 0.61 spring), followed by body mass (0.64 autumn; 0.53 spring), and then body fat (0.22 autumn; 0.01 spring). High repeatability in body and lean mass likely reflects primary structural composition, which is conserved across seasons. Low repeatability of body fat supports that it is the primary labile source of energy that is largely a product of environmental contributions of the previous season. Based on the disparate levels in repeatability among nutritional biomarkers, we contend that body and lean mass are better indicators of nutritional legacies (e.g., maternal effects), whereas body fat is a direct and sensitive reflection of recent nutritional gains and losses.

Sagebrush (Artemisia spp.)-dominated habitats in the western United States have experienced extensive, rapid changes due to development of natural-gas fields, resulting in localized declines of greater sage-grouse (Centrocercus urophasianus) populations. It is unclear whether population declines in natural-gas fields are caused by avoidance or demographic impacts, or the age classes that are most affected. Land and wildlife management agencies need information on how energy developments affect sage-grouse populations to ensure informed land-use decisions are made, effective mitigation measures are identified, and appropriate monitoring programs are implemented (Sawyer et al. 2006). We used information from radio-equipped greater sage-grouse and lek counts to investigate natural-gas development influences on 1) the distribution of, and 2) the probability of recruiting yearling males and females into breeding populations in the Upper Green River Basin of southwestern Wyoming, USA. Yearling males avoided leks near the infrastructure of natural-gas fields when establishing breeding territories; yearling females avoided nesting within 950 m of the infrastructure of natural-gas fields. Additionally, both yearling males and yearling females reared in areas where infrastructure was present had lower annual survival, and yearling males established breeding territories less often, compared to yearlings reared in areas with no infrastructure. Our results supply mechanisms for population-level declines of sage-grouse documented in natural-gas fields, and suggest to land managers that current stipulations on development may not provide management solutions. Managing landscapes so that suitably sized and located regions remain undeveloped may be an effective strategy to sustain greater sage-grouse populations affected by energy developments.

Context Natural selection favors species with strong fidelity to seasonal ranges where resources are predictable across space and time. Extreme disturbance events may negate the fitness benefits of faithfulness—with consequences for population distributions. Objectives We hypothesized that extreme events fragment population distributions through two mechanisms: (1) reductions in fidelity or (2) elevated mortality. We tested the relative contributions of these mechanisms to population dynamics of mule deer ( Odocoileus hemionus )—a long-lived mammal—with long-term, individual-based information before and after disturbance occurred. Methods We evaluated our hypotheses in response to disturbance during winter using a unique dataset of the movement and fate of adult females from a migratory population of mule deer over 8 years in western Wyoming, USA. First, we calculated fidelity of individuals between progressive winters and identified vacant space between population-level ranges to represent gaps in the population distribution. We then assessed: (1) how internal state and disturbance conditions affected fidelity, (2) how internal state, disturbance conditions, and fidelity affected survival, and (3) how survival and fidelity affected creation of gaps in population distribution. Results Disturbance weakened fidelity, but fidelity did not affect survival. Nutritional condition and age affected survival. Weakened fidelity did not change population distribution; rather, nutritional condition underpinned population dynamics, meaning that behavior alone may not prevent the creation of gaps in distribution following extreme disturbances. Conclusions Extreme events may render behavioral plasticity incapable of mitigating mortality risk, and the environmental conditions that animals experience during the months, seasons, or even years before an event may regulate population-level organization in its aftermath.

The area near Pinedale, Wyoming, in the upper Green River Basin has some of the highest densities of greater sage-grouse in the world. Decreasing counts of males attending leks and evidence of overall population reductions, coupled with increasing natural gas development, have raised concern for conservation of greater sage-grouse in the area. Low yearling recruitment could be causing a decline in the numbers of birds using leks near natural gas development. This study investigated recruitment of males and females to determine if they continued to breed in areas with natural gas development, were displaced to other areas to breed, or did not breed at all. Results indicated that yearling males tended to avoid leks highly immersed into developing gas fields. Females that bred or nested in the gas fields had later nest hatching dates and fewer and smaller broods than birds outside the fields. Both males and females showed low fidelity to natal leks and nest sites. This study suggested that assessing the potential influence of a natural gas field on greater sage-grouse should involve multiple variables to describe the developing field and incorporate the cumulative effects they may have on lek use as the spatial orientation of the leks relative to the developing field changes over time.