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Large ungulate migrations occur across continents and inspire curiosity about how these animals know when to leave and where to go. Jesmer et al. took advantage of regional extinctions and reintroductions of several North American ungulate species to determine the role of learning in migrations (see the Perspective by Festa-Bianchet). Reintroduced populations of bighorn sheep and moose did not migrate as historical herds had. However, after several decades, newly established herds were better able to track the emergence of vegetation in the environment and were increasingly migratory. Thus, newly introduced animals learned about their environment and shared the information through social exchange. Science , this issue p. 1023 ; see also p. 972 Bighorn sheep and moose learn their migration routes through culture and experience. Ungulate migrations are assumed to stem from learning and cultural transmission of information regarding seasonal distribution of forage, but this hypothesis has not been tested empirically. We compared the migratory propensities of bighorn sheep and moose translocated into novel habitats with those of historical populations that had persisted for hundreds of years. Whereas individuals from historical populations were largely migratory, translocated individuals initially were not. After multiple decades, however, translocated populations gained knowledge about surfing green waves of forage (tracking plant phenology) and increased their propensity to migrate. Our findings indicate that learning and cultural transmission are the primary mechanisms by which ungulate migrations evolve. Loss of migration will therefore expunge generations of knowledge about the locations of high-quality forage and likely suppress population abundance.

Patterns of resource selection are driven by the decision-making processes of animals occurring at multiple scales from where to establish a home range (i.e., second order selection) to which resource patches to use within the home range (i.e., third order selection). Elk (Cervus canadensis) were reintroduced to southwestern Virginia, USA, from 2012 to 2014 following successful translocations onto reclaimed surface coal mines in the region. We sought to understand how elk have acclimated following their translocation using location data from GPS-collared adult female elk (n = 33) collected from 2019 to 2022 along with remotely sensed terrain and land cover data. We utilized continuous-time movement models paired with generalized linear mixed-effects modeling to describe seasonal resource selection at second and third orders. At both scales of selection and throughout the year, female elk selected reclaimed surface mines, conifer forests, ridgetops, and areas with lower terrain roughness, while avoiding mixed hardwood and oak (Quercus spp.) forests. Unmined open land was only selected at the third order during periods of forage scarcity (i.e., winter) and increased metabolic requirements (i.e., late gestation). Although surface coal mining leaves legacy environmental impacts on the landscape, management of these sites provides benefits to elk and maintains open habitat that is otherwise limited.

For ungulates and other long-lived species, life-history theory predicts that nutritional reserves are allocated to reproduction in a state-dependent manner because survival is highly conserved. Further, as per capita food abundance and nutritional reserves decline (i.e., density dependence intensifies), reproduction and recruitment become increasingly sensitive to weather. Thus, the degree to which weather influences vital rates should be associated with proximity to nutritional carrying capacity—a notion that we refer to as the Nutritional Buffer Hypothesis. We tested the Nutritional Buffer Hypothesis using six moose (Alces alces) populations that varied in calf recruitment (33–69 calves/100 cows). We predicted that populations with high calf recruitment were nutritionally buffered against the effects of unfavorable weather, and thus were below nutritional carrying capacity. We applied a suite of tools to quantify habitat and nutritional condition of each population and found that increased browse condition, forage quality, and body fat were associated with increased pregnancy and calf recruitment, thereby providing multiple lines of evidence that declines in calf recruitment were underpinned by resource limitation. From 2001 to 2015, recruitment was more sensitive to interannual variation in weather (e.g., winter severity, drought) and plant phenology (e.g., duration of spring) for populations with reduced browse condition, forage quality, and body fat, suggesting these populations lacked the nutritional reserves necessary to buffer demographic performance against the effects of unfavorable weather. Further, average within-population calf recruitment was determined by regional climatic variation, suggesting that the pattern of reduced recruitment near the southern range boundary of moose stems from an interaction between climate and resource limitation. When coupled with information on habitat, nutrition, weather, and climate, life-history theory provides a framework to estimate nutritional limitation, proximity to nutritional carrying capacity, and impacts of climate change for ungulates.

Ungulate migrations are crucial for maintaining abundant populations and functional ecosystems. However, little is known about how or why migratory behaviour evolved in ungulates. To investigate the evolutionary origins of ungulate migration, we employed phylogenetic path analysis using a comprehensive species-level phylogeny of mammals. We found that 95 of 207 extant ungulate species are at least partially migratory, with migratory behaviour originating independently in 17 lineages. The evolution of migratory behaviour is associated with reliance on grass forage and living at higher latitudes wherein seasonal resource waves are most prevalent. Indeed, originations coincide with mid-Miocene cooling and the subsequent rise of C 4 grasslands. Also, evolving migratory behaviour supported the evolution of larger bodies, allowing ungulates to exploit new ecological space. Reconstructions of migratory behaviour further revealed that seven of ten recently extinct species were probably migratory, suggesting that contemporary migrations are important models for understanding the ecology of the past. The authors examine present and past drivers of ungulate migratory behaviour, finding that current migratory ungulates are larger, more grass-dependent and live at higher latitudes on average than non-migrants, and that migration probably emerged after the rise of C 4 grasslands and increased seasonality towards the poles.

Glucocorticoids (GC) and triiodothyronine (T3) are two endocrine markers commonly used to quantify resource limitation, yet the relationships between these markers and the energetic state of animals has been studied primarily in small-bodied species in captivity. Free-ranging animals, however, adjust energy intake in accordance with their energy reserves, a behavior known as state-dependent foraging. Further, links between life-history strategies and metabolic allometries cause energy intake and energy reserves to be more strongly coupled in small animals relative to large animals. Because GC and T3 may reflect energy intake or energy reserves, state-dependent foraging and body size may cause endocrine–energy relationships to vary among taxa and environments. To extend the utility of endocrine markers to large-bodied, free-ranging animals, we evaluated how state-dependent foraging, energy reserves, and energy intake influenced fecal GC and fecal T3 concentrations in free-ranging moose (Alces alces). Compared with individuals possessing abundant energy reserves, individuals with few energy reserves had higher energy intake and high fecal T3 concentrations, thereby supporting state-dependent foraging. Although fecal GC did not vary strongly with energy reserves, individuals with higher fecal GC tended to have fewer energy reserves and substantially greater energy intake than those with low fecal GC. Consequently, individuals with greater energy intake had both high fecal T3 and high fecal GC concentrations, a pattern inconsistent with previous documentation from captive animal studies. We posit that a positive relationship between GC and T3 may be expected in animals exhibiting state-dependent foraging if GC is associated with increased foraging and energy intake. Thus, we recommend that additional investigations of GC– and T3–energy relationships be conducted in free-ranging animals across a diversity of body size and life-history strategies before these endocrine markers are applied broadly to wildlife conservation and management.

Subspecies designations within temperate species' ranges often reflect populations that were isolated by past continental glaciation, and glacial vicariance is believed to be a primary mechanism behind the diversification of several subspecies of North American cervids. We used genetics and the fossil record to study the phylogeography of three moose subspecies (Alces alces andersoni, A. a. gigas, and A. a. shirasi) in western North America. We sequenced the complete mitochondrial genome (16,341 base pairs; n = 60 moose) and genotyped 13 nuclear microsatellites (n = 253) to evaluate genetic variation among moose samples. We also reviewed the fossil record for detections of all North American cervids to comparatively assess the evidence for the existence of a southern refugial population of moose corresponding to A. a. shirasi during the last glacial maximum of the Pleistocene. Analysis of mtDNA molecular variance did not support distinct clades of moose corresponding to currently recognized subspecies, and mitogenomic haplotype phylogenies did not consistently distinguish individuals according to subspecies groupings. Analysis of population structure using microsatellite loci showed support for two to five clusters of moose, including the consistent distinction of a southern group of moose within the range of A. a. shirasi. We hypothesize that these microsatellite results reflect recent, not deep, divergence and may be confounded by a significant effect of geographic distance on gene flow across the region. Review of the fossil record showed no evidence of moose south of the Wisconsin ice age glaciers ≥ 15,000 years ago. We encourage the integration of our results with complementary analyses of phenotype data, such as morphometrics, originally used to delineate moose subspecies, for further evaluation of subspecies designations for North American moose.

Rapid climate and human land-use change may limit the ability of long-distance migratory herbivores to optimally track or 'surf' high-quality forage during spring green-up. Understanding how anthropogenic and environmental stressors influence migratory movements is of critical importance because of their potential to cause a mismatch between the timing of animal movements and the emergence of high-quality forage. We measured stress hormones (fecal glucocorticoid metabolites; FGMs) to test hypotheses about the effects of high-quality forage tracking, human land-use and use of stopover sites on the physiological state of individuals along a migratory route. We collected and analysed FGM concentrations from 399 mule deer ( ) samples obtained along a 241-km migratory route in western Wyoming, USA, during spring 2015 and 2016. In support of a fitness benefit hypothesis, individuals occupying areas closer to peak forage quality had decreased FGM levels. Specifically, for every 10-day interval closer to peak forage quality, we observed a 7% decrease in FGMs. Additionally, we observed support for both an additive anthropogenic stress hypothesis and a hypothesis that stopovers act as physiological refugia, wherein individuals sampled far from stopover sites exhibited 341% higher FGM levels if in areas of low landscape integrity compared to areas of high landscape integrity. Overall, our findings indicate that the physiological state of mule deer during migration is influenced by both anthropogenic disturbances and their ability to track high-quality forage. The availability of stopovers, however, modulates physiological responses to those stressors. Thus, our results support a recent call for the prioritization of stopover locations and connectivity between those locations in conservation planning for migratory large herbivores.

Forests in the Sierra Nevada, similar to those across the continent, have been substantially altered by logging, fire exclusion, and other human activities. Current forest management emphasizes maintenance or restoration of resiliency in the face of contemporary disturbance factors that include wildfire, climate change, continued urbanization, and invasive species. We evaluated responses of small mammals to forest management by monitoring a series of 12 replicate trapping grids in compositionally homogeneous forest over 8 years, and implemented 2 levels of canopy thinning. Livetrapping efforts (119,712 trap-nights) yielded 15,613 captures of 2,305 individuals of 13 species, and although forest structure was significantly influenced by canopy treatments, small mammal numbers and assemblage composition were not. To better understand this we assessed habitat associations of small mammals at 599 census points on 75 transects established in a stratified random manner throughout Plumas National Forest. We analyzed these data with 2 complementary forms of constrained ordination (canonical correspondence and canonical correlation) that extract major gradients in 1 data set (e.g., distribution of small mammal captures) and explain these in terms of measured variables from a 2nd data set (e.g., habitat and environmental measurements). Over 3 years and 57,504 trap-nights of effort we captured 1,367 individuals of 11 species. Both forms of ordination exposed significant associations between small mammals and underlying habitat metrics, but they explained remarkably little variation in these data, suggesting that small mammals are responding only modestly to habitat variation as expressed by the available environmental variables measured at each plot. We followed this with stepwise multiple Poisson regression to build models of habitat associations of these species. We applied model-averaging and employed Akaike's information criterion corrected for small sample size (AICc) to evaluate candidate models. Reflecting ordination results, competitive models (e.g., those with Akaike differences [ΔAICc] < 2.0) cumulatively explained little variation (12–36%) and regression coefficients were very low. Hence, both ordination and Poisson multiple regression suggest that the limited response by small mammals to canopy thinning primarily reflects the generalist habits of the common species in this forest. We propose that anthropogenic influences have led to structural homogenization of these forests, even across > 800 m of elevation, such that habitat specialists (e.g., old-forest–dependent species such as Myodes [Clethrionomys] californicus and Glaucomys sabrinus) have become less common due to the lack of suitable habitat. Further efforts should target nonforested habitats (meadows and riparian corridors), but results presented here suggest that managers should strive to increase heterogeneity at large spatial scales and especially to promote the development of mature forest structure.

The golden-mantled ground squirrel (Callospermophilus lateralis) is considered an asocial species, characterized by agonistic interactions, nonsharing of territories and early dispersal. The species is poorly studied, so we used radiotelemetry to determine home range size, home range overlap and dispersal. Home ranges of 12 adult females averaged 3.75 ha (range  =  1.14–13.52) using the 95% fixed kernel method. Home ranges overlapped substantially but core areas did not, indicating territoriality may be expressed over only a portion of the home range, and an index of dynamic interaction was neutral, indicating neither attraction nor avoidance between females. Most (80%) of 20 juveniles dispersed during their first summer, but some delayed dispersal until at least their yearling summer. Our results provide support for the classification of golden-mantled ground squirrels as asocial but suggest that the expression of territoriality and early dispersal may be variable.

Consumer-resource dynamics are central to the understanding of behavioral, nutritional, and population ecology. Nevertheless, many critical gaps in knowledge remain about the consumer-resource dynamics of large herbivores because their large body size, expansive space use, and slow life histories hinder experimental manipulation. The growth rate of moose (Alces alces) populations across the Intermountain West and other areas of North America has been declining over the past thirty years, but recent (30 to 80 years) translocations of moose have resulted in some relatively small, rapidly growing populations. These translocations therefore created a natural experiment whereby the relationship between resources and the behavior, nutritional, and demography of large-herbivore consumers was evaluated. In chapter one, I integrated a suite of field, laboratory, and remote-sensing techniques with life history theory to understand the role of resource limitation in declining moose recruitment. I found that simple browse surveys and fecal-based measures of forage quality and pregnancy were correlated with recruitment, indicating that these tools can be used to monitor resource limitation. Further, I found that recruitment was dictated ubiquitously by inter-annual variation in weather and regional differences in climate (i.e., average, long-term weather conditions), signifying that all populations were near nutritional carrying capacity. In chapter two, I show how metabolic allometries and state-dependent foraging behavior alter energy-endocrine profiles in large herbivores. Consequently, this chapter both contributes to knowledge about the behavior of large herbivores and illustrates that applying laboratory models of energy-endocrine relationships to large-bodied, free-ranging animals may result in erroneous inference regarding their nutritional condition and proximity to carrying capacity. My third chapter continues to explore how resource limitation influences the foraging behavior of moose by quantifying how diet selection changes as intraspecific competition intensifies and resources become increasingly limiting. Contrary to the Niche Variation Hypothesis, and in accordance with Optimal Foraging Theory, moose broaden their diet selection under resource limitation by increasing individual diet breadth rather than forming into groups of specialized individuals that collectively forage on a wide variety of foods. Although the Niche Variation Hypothesis has gained much attention over the past two decades, my work indicates that inheritance of behavioral or morphological traits associated with foraging (i.e., dietary phenotype) underlie dietary specialization and the Niche Variation Hypothesis; when inheritance of dietary phenotype is weak, populations forage in accordance with Optimal Foraging Theory and individual diet breadth broadens under resource limitation. My fourth chapter tested a long-standing hypothesis in ungulate ecology that predicts migratory behavior is socially learned and culturally transmitted across generations. This hypothesis, however, had not be tested empirically. Using GPS collar data, I compared the migratory propensity of individual moose and bighorn sheep (Ovis canadensis) that were translocated from migratory populations into novel landscapes with the migratory propensity of individuals residing in historical populations that had persisted for at least 200 years. I also compared the ability of individuals to track high-quality, green forage across topographic gradients—a behavior known as “green-wave surfing” that was hypothesized to be a precursor to migration. Individuals failed to migrate when first translocated, but over time (decades) the surfing ability of translocated populations increased and individuals began migrating. Thus, my work demonstrates that the migrations of large herbivores are learned and culturally transmitted from generation to generation, indicating that conservation of migration corridors not only protects the landscapes that these iconic animals depend on, such efforts also maintain the traditional knowledge that migratory animals use to bolster fitness and sustain abundant populations.