Long-term studies provide us with crucial information for understanding mammalian biology, which is often lacking from short-term studies. In this Special Feature we focus on 7 mammalian taxa and review ways longterm studies have contributed to our knowledge of ecophysiology, social systems, population and community processes, and conservation. Our aims are to highlight the ways long-term studies on mammals have informed theory, to identify missing information needed to advance theory, and to suggest directions for future long-term studies on mammals.

Elephants may live for > 60 years, so it is obvious that long-term studies are necessary if we are to understand their life histories. Here, I review long-term population studies, most based on individual elephants, to show the wealth of detailed mechanisms that such studies can reveal. This review is biased toward African savanna elephants, a reflection of existing long-term studies on elephants worldwide. Besides life histories, there are 2 aspects of elephant biology that are illuminated by long-term field studies (not necessarily those based on individual elephants). First is knowledge of spatial dynamics of populations that occur in response to environmental change (climatic or anthropogenic), such as density dependence that is associated with the distribution of surface water or responses to specific management decisions, and second is the effects these ecosystem engineers have on habitats, landscapes, other species, and ultimately on ecosystems. I also argue that these long-term data are crucial to inform conservation policies and associated management actions, such as changes in water-pumping strategies, landscape management, and control of elephant populations.

Studies of marked free-ranging ungulates have provided major contributions to ecology, evolution, and conservation. We focus on research areas where these studies have been particularly important: the role of individual differences in population dynamics, temporal changes in factors limiting populations, variation in reproductive success, quantitative genetics in the wild, population management, and conservation. We underline some strengths and limitations of these studies and call for more research on populations subjected to hunting, coexisting with large predators, and living in tropical or arid environments. Long-term research on ungulates requires long-term commitment, funding, access to study areas where animals can be monitored, and, usually, support from government agencies. Logistical difficulties limit the number of these important studies.

Although aquatic mammals are elusive subjects, long-term studies of cetaceans have revealed remarkable lifehistory traits, including long life spans, bisexual philopatry, prolonged maternal care, and even menopause. Long-term cetacean research, defined here as studies lasting ≥ 10 years, has also helped shape our understanding of large multilevel societies, fission-fusion dynamics, cultural processes, complex sociality, and cognition. Yet relative to their terrestrial counterparts, little is known about many cetacean societies, especially pelagic species; similarly, collection of biological samples (such as blood, feces, urine) from live subjects is rarely possible. Cetaceans have been severely impacted by human activities, from commercial whaling to fisheries bycatch, prey depletion, habitat loss, and chemical and noise pollution. Longitudinal research, defined as measuring the same individuals repeatedly over time, can provide vital information necessary for devising viable solutions for mitigating these impacts and promoting sustainable practices. This review evaluates key findings gleaned from continuous and systematic longitudinal studies of free-living cetaceans. We present examples for each topic, though our condensed review cannot be comprehensive. Given their adaptations to the marine environment, slow life histories, and complex societies, continued investment in long-term research is vital for both understanding and protecting this taxonomic group.

Most carnivorans (members of the mammalian order Carnivora) are elusive and long lived, so long-term studies are required to understand their basic biology and, ultimately, to conserve them. Here, we review examples of the wealth of information about the social systems, ecophysiology, and ecology of gregarious, terrestrial, carnivorous carnivorans (hereafter, carnivores) generated by long-term field studies of free-living, individually recognizable carnivores. Our synthesis yields key insights about the evolutionary forces favoring cooperation and ecological forces shaping social dynamics. The genetic assignment of parentage permits elucidation of the extent of reproductive skew in natural populations spanning multiple generations. Tracking of individuals across their life spans reveals underlying physiological, behavioral, and ecological mechanisms mediating reproductive suppression and dispersal. Long-term studies permit a comprehensive understanding of the ways in which intrinsic and extrinsic factors, including conflict with humans, regulate carnivore populations. Long-term studies also provide crucial baseline information required for the conservation of carnivores in the face of burgeoning human populations and global climate change. Notably, many conservation problems unfold on timescales only addressable with long-term data. Although we have yet to exploit the full wealth of information from long-term field studies, these valuable repositories have already yielded myriad insights about mammalian carnivores that would be unobtainable from studies conducted over shorter timescales.

Long-term studies on rodents have been conducted for longer periods (up to 70 years) and more generations (up to 88 generations) than for most other mammalian taxa. These studies have been instrumental in furthering our understanding of ecophysiology, social systems, and population and community processes. Studies on African striped mice (Rhabdomys pumilio) revealed that basal blood glucose levels span a far greater homeostatic range than previously thought. Studies on American red squirrels (Tamiasciurus hudsonicus) demonstrated how endocrine pathways underlying phenotypic plasticity allow individuals to respond to different environments. Long-term studies on African striped mice, marmots (Marmota), tuco-tucos (Ctenomys sociabilis), and degus (Octodon degus) revealed that ecological constraints on dispersal are drivers of group formation in some species but not others. Social flexibility, when the social system of an entire population can change due to individuals changing their social tactics, has been demonstrated in striped mice. Long-term studies on prairie voles (Microtus ochrogaster) found that males and females often live in pairs, leading to subsequent studies of the neural mechanisms underlying social monogamy. Long-term studies on other arvicoline rodents contributed more to our understanding of the factors influencing population dynamics than studies on any other mammalian order. While food availability and predation have been identified as factors influencing population dynamics, no single factor alone drives population dynamics in any species. We encourage researchers to incorporate manipulative experiments into long-term studies and to take integrative approaches to inform cross-disciplinary theory.

Simian primates (monkeys and apes) are typically long-lived animals with slow life histories. They also have varying social organization and can slowly impact their environment by either being seed dispersers or by overbrowsing their food trees. As a result, short-term studies and those focusing on just 1 location only provide a snapshot of simian life under a specific set of ecological conditions that typically do not represent the complete spatial and temporal picture. Long-term field studies are needed to obtain a true understanding of their behavior, life history, ecology, and the selective pressures acting on them. Fortunately, there have been many long-term studies of simians, so a great deal is known about many species. Here, we consider examples of long-term studies that have operated continuously for approximately a decade or more. We review studies that deal with ecophysiology, social organization, population and community ecology, or conservation. The information emerging from these sites is particularly helpful in the construction of informed conservation plans, which are desperately needed given the severity of threats to simians and the fact that responses do not occur over the duration of a Ph.D. or granting cycle (typically 1–3 years).

Lemurs, lorises, and tarsiers are socially and ecologically diverse primates that include some of the most endangered mammals. We review results of long-term studies of 15 lemur species from 7 sites in Madagascar and 1 species each of loris and tarsier in Indonesia. We emphasize that the existence of long-term study populations is a crucial prerequisite for planning and conducting shorter studies on specific topics, as exemplified by various ecophysiological studies of lemurs. Extended studies of known individuals have revealed variation in social organization within and between ecologically similar species. Even for these primates with relatively fast life histories, it required more than a decade of paternity data to characterize male reproductive skew. The long-term consequences of female rank on reproductive success remain poorly known, however. Long-term monitoring of known individuals is the only method to obtain data on life-history adaptations, which appear to be shaped by predation in the species covered here; long-term studies are also needed for addressing particular questions in community ecology. The mere presence of long-term projects has a positive effect on the protection of study sites, and they generate unique data that are fundamental to conservation measures, such as close monitoring of populations.

Long-term individual-based field studies are essential for understanding how animals are adapted to their natural environment and how they will adapt in the future. Long-term studies conducted on more than 200 mammalian species have accumulated 11,000 study years and covered more than 17,000 generations. They have been dominated by studies on social systems and population biology, with little research on ecophysiology—typically, ecophysiological studies are short-term projects embedded in long-term studies. However, physiological data are necessary for understanding how mammals respond to rapid global changes. This is especially important in conservation, for which long-term monitoring of natural populations is essential. Maintaining a successful long-term study requires an understanding of the unique “life history” of long-term studies. Like short-term studies, long-term studies progress from onset to end, but long-term studies differ in the way they are maintained. The greatest challenge to long-term research is the need for consistent and regular funding. Long-term research also requires principal investigators with strong organizational skills, productive collaborations, and creative ways of maintaining financial support. We address challenges and discuss strategies, some based on our own experiences, for the successful management and life history of long-term studies.

Solitary carnivores in the family Mustelidae are thought to exhibit pronounced intrasexual territoriality, defending space against competitors but tolerating members of the opposite sex. Although mustelids move long distances daily, how such movements reflect intrasexual territoriality is relatively unknown. We hypothesized that martens make regular movements around the boundaries of their territories and that territories typically would be stable across seasons and years. Consequently, we predicted that high-resolution movement data would reveal territorial boundaries within days to weeks. We collected movement data (from GPS collars) and long-term location data (from VHF collars) for 25 adult Pacific martens (Martes caurina) in 2 study areas (coastal and montane). We used GPS movement data to estimate utilization distributions and evaluate individual overlap and stability of territories between seasons, and compared those with annual home ranges from VHF locations. We also used incremental analysis to calculate how many days of movement data were required to fully describe a marten's territory. Marten territories estimated from GPS movement data were indistinguishable from annual home ranges (spatial overlap, ± SD, 0.99 ± 0.13, n = 9) and remained relatively stable year-round with some expansion during winter. Territories of same-sex neighbors overlapped < 2%. Our models suggested that an individual marten's movements encompassed 95% of its territory within 2.25–14 days ( = 4.6 days); that time did not differ between study areas, sexes, or seasons. Location data with high spatial and temporal resolution could enable more precise estimates of territoriality in this and potentially other carnivore species, and illuminate hitherto unobservable behavioral differences across time and space.

Carnivores exhibit strong interspecific competition and partition niche axes to minimize agonistic interactions. Niche partitioning, though, is contingent upon resource heterogeneity, and recent landscape homogenization may limit the abilities of carnivores to partition niche space. The negative fitness consequences associated with niche overlap may be particularly problematic for repatriating carnivores, and could delay the recovery of rare or endangered species. American martens (Martes americana) and fishers (Pekania pennanti) are the most commonly translocated carnivores in North America and both were reintroduced to a highly modified landscape in Wisconsin, United States. To date, fishers have flourished while martens remain endangered. To assess the role of competition in marten recovery, we used a combination of occupancy modeling, point pattern analyses, and stable isotope analyses to assess 5 coexistence mechanisms: spatial segregation, dietary segregation, temporal avoidance, and differential use of habitat and snow features. Over 7 years, we observed consistently high fisher occupancy and consistently low marten occupancy. Moreover, martens and fishers overlapped in their use of space and time, and neither exhibited habitat preferences. Isotopic analyses revealed complete dietary overlap, with martens falling entirely within the isotopic niche of fishers. Deep, uncompressed snow, however, had a negative effect on fisher activity. We propose that extensive landscape homogenization has resulted in niche compression and that marten recovery has been limited by increased competition with fishers. Restoration programs often overlook competitive interactions, but our results emphasize the importance of interspecific competition for recovering carnivore populations and highlight the challenge of reconstructing carnivore communities in increasingly homogenized landscapes.

Rapidly changing environmental conditions are influencing distributions of wildlife species in Alaska. Due to strict physiological requirements, the distribution of American martens (Martes americana) is theorized to be driven by changing habitat, climate, and other anthropogenic conditions. We aimed to quantify marten distributions on the Kenai Peninsula, Alaska, and compared historic and contemporary occurrence records. To illustrate changing distribution patterns, we developed predictive niche models for 2 decades and investigated patterns by relating environmental trends with predicted distributions. Museum and trapping records, supplemented by aerial videography detections for martens on the Kenai over the past century, served to train RandomForests-based niche models for 1988–2001 and 2002–2010. Change-detection analyses revealed an ongoing westward expansion of likely marten distribution on the Kenai Peninsula since at least 1988, and historic records indicated longer-term growth. Top predictors in the models included soil ecotype, landcover, distance to trails, and distance to recreation sites. Our research suggests that on the Kenai Peninsula, marten distribution is responding to a combination of landscape and climate effects that have contributed to expanding marten distributions over the past century.

Effective conservation of insular populations requires careful consideration of biogeography, including colonization histories and patterns of endemism. Across the Pacific Northwest of North America, Pacific martens (Martes caurina) and American pine martens (Martes americana) are parapatric sister species with distinctive postglacial histories. Using mitochondrial DNA and 12 nuclear microsatellite loci, we examine processes of island colonization and anthropogenic introductions across 25 populations of martens. Along the North Pacific Coast (NPC), M. caurina is now found on only 2 islands, whereas M. americana occurs on mainland Alaska and British Columbia and multiple associated islands. Island populations of M. caurina have a longer history of isolation reflected in divergent haplotypes, private microsatellite alleles, and relatively low within-population diversity. In contrast, insular M. americana have lower among-population divergence and higher metrics of within-population diversity. On some NPC islands, introductions of M. americana may be related to decline of M. caurina. Long-term persistence of these species likely has been influenced by anthropogenic manipulations, including wildlife translocations and industrial-scale deforestation, yet, the distinctive histories of these martens have not been incorporated into natural resource policies.

The “blind mouse” genus, Typhlomys, is an ancient taxon in the family Platacanthomyidae, comprising 2 living species and 4 living subspecies. We sequenced 3 mitochondrial (CytB, COI, and ND₂) and 2 nuclear (GHR and IRBP) gene segments to estimate the phylogenetic relationships of the species and subspecies, and to delimit species boundaries. We also evaluated patterns of morphological and morphometric variation of the skull. The molecular results suggest at least 5 species are present, corresponding to the 2 recognized species (Typhlomys cinereus and T. chapensis), 1 species previously considered a subspecies (T. ci. daloushanensis), 1 new species (Typhlomys nanus sp. nov.), and 1 putative new species, for which we lack adequate morphological specimens. We also determined that the subspecies Typhlomys cinereus jingdongensis is conspecific with T. chapensis. Diversification of the genus occurred in the late Miocene and Pliocene. The new species, T. nanus, is distributed in eastern and northeastern Yunnan at middle to high elevations (2,000 m to > 3,000 m above sea level). Interestingly, we detected a frameshift mutation within the IRBP gene, which is the 1st molecular evidence for the degradation of vision.

The ability to recognize individuals within an animal population is fundamental to conservation and management. Identification of individual bats has relied on artificial marking techniques that may negatively affect the survival and alter the behavior of individuals. Biometric systems use biological characteristics to identify individuals. The field of animal biometrics has expanded to include recognition of individuals based upon various morphologies and phenotypic variations including pelage patterns, tail flukes, and whisker arrangement. Biometric systems use 4 biologic measurement criteria: universality, distinctiveness, permanence, and collectability. Additionally, the system should not violate assumptions of capture–recapture methods that include no increased mortality or alterations of behavior. We evaluated whether individual bats could be uniquely identified based upon the collagen–elastin bundles that are visible with gross examination of their wings. We examined little brown bats (Myotis lucifugus), northern long-eared bats (M. septentrionalis), big brown bats (Eptesicus fuscus), and tricolored bats (Perimyotis subflavus) to determine whether the “wing prints” from the bundle network would satisfy the biologic measurement criteria. We evaluated 1,212 photographs from 230 individual bats comparing week 0 photos with those taken at weeks 3 or 6 and were able to confirm identity of individuals over time. Two blinded evaluators were able to successfully match 170 individuals in hand to photographs taken at weeks 0, 3, and 6. This study suggests that bats can be successfully re-identified using photographs taken at previous times. We suggest further evaluation of this methodology for use in a standardized system that can be shared among bat conservationists.

Information on the roost requirements of small, temperate-zone hibernating bats, which can spend up to 8 months in hibernation, is crucial to their conservation. We studied male big brown bats (Eptesicus fuscus) in southeastern Alberta, Canada, to investigate the physical and microclimate characteristics of hibernacula used by this species in a prairie river valley (Dinosaur Provincial Park, DPP). We monitored roosting behavior and movement, and also compared microclimate conditions (temperature and humidity) within these crevice hibernacula to those of random crevices within the study area, and to conditions inside 4 known cave hibernacula in central and northern Canada. Our results show that male E. fuscus in DPP use rock-crevice hibernacula with less variable temperatures than ambient and random crevice temperatures, with evidence of winter roost fidelity within and between years. Bats used only 3 hibernacula and, although mid-winter flight is common in our study area, there was little movement by bats between hibernacula. Rock-crevice hibernacula were warmer and more thermally stable than other available crevices in DPP, and drier but not necessarily colder than known cave hibernacula elsewhere. Our study is the first to examine crevice roost selection by bats during winter, and suggests that specific hibernacula are important for individual bats, despite the fact that numerous crevices are available.

The pampas deer (Ozotoceros bezoarticus) is native to South America and is endangered in Argentina. In Buenos Aires province, Argentina, the last population of pampas deer is harbored in the Bahía Samborombón Wildlife Refuge (BSWR), which includes protected areas and numerous cattle ranches. This population has been declining and changing progressively in its distribution since 1985, and negative interactions between pampas deer and introduced ungulates (livestock and feral pigs) have been proposed among the main causes of its decline. We examined the abundance, distribution, and interactions among pampas deer, cattle, and feral pigs at site and landscape scales in the BSWR. At the site scale, coexistence between pampas deer and cattle at the same paddock was only possible at moderate stocking rates (0.2–0.4 AU/ha), and no deer were recorded at paddocks when stocking rates were above 0.6 AU/ha. Pampas deer and feral pigs co-occurred more frequently, but deer switched their behavior and increased levels of surveillance in response to proximity of feral pigs. At the landscape scale, a clear spatial segregation and differential distribution was detected among pampas deer, cattle, and feral pigs along the BSWR. Our results suggest that the current distribution of pampas deer at the study area is a consequence of avoiding contact with both livestock and feral pigs at the site scale. Thus, negative interactions recorded between pampas deer and introduced ungulates at the site scale were expressed at the landscape scale. Both in situ and ex situ conservation efforts are urgently needed to conserve pampas deer.

The giant armadillo (Priodontes maximus) is the largest extant armadillo species. This rare, cryptic, and poorly studied South American mammal is considered a physical ecosystem engineer. From February to August 2014, 10 camera traps were used to estimate population density, activity patterns, and the ecological importance of giant armadillos on private lands with riparian forests and natural savannas near Puerto Gaitán (Meta), in the Eastern Llanos of Colombia. A total of 5,728 records (photos and videos) were obtained during 1,335 trap nights, 7.4% of which corresponded to giant armadillos and 92.6% to other vertebrate species. The 426 records of Priodontes, grouped in 78 events (uncorrelated records), were used to individually identify 11 individuals in an area of 189 km² and determine their activity periods. Population density was estimated at 5.8 animals/100 km². Nocturnal habits, mainly between 22:00 and 00:00 h, were predominant. A total of 470 km walking transects, censuses of burrows and other indirect signs of presence, and camera trapping allowed determination of some aspects of habitat use. Priodontes prefers riparian forest habitats, makes burrows of 42.0 ± 5.9 cm width and 35.0 ± 5.9 cm height in sloped terrain, and re-uses burrows. More than 26 different species were associated with Priodontes burrows. The conservation of riparian forests is fundamental for the persistence of P. maximus populations and the ecological community that is associated with its burrows.

Catastrophic natural events can have profound impacts on patterns of genetic diversity. Due to the typically unpredictable nature of such phenomena, however, few studies have been able to directly compare patterns of diversity before and after natural catastrophic events. Here, we examine the impacts of a recent volcanic eruption in southern Chile on genetic variation in the colonial tuco-tuco (Ctenomys sociabilis), a subterranean species of rodent endemic to the area most affected by the June 2011 eruption of the Puyehue-Cordón Caulle volcanic complex. To provide a comparative context for interpreting changes in genetic variation in this species, we also analyze the effects of this eruption on genetic variation in the geographically proximate but more widely distributed Patagonian tuco-tuco (C. haigi). Our analyses indicate that while both C. sociabilis and C. haigi displayed significant post-eruption decreases in population density, the apparent impacts of the eruption on genetic diversity differed between species. In particular, genetic diversity at multiple microsatellite loci increased in C. sociabilis after the eruption while no comparable post-eruption increase in C. haigi was observed at these loci. No changes in post-eruption diversity at the mitochondrial cytochrome b locus were detected for either species. To place these findings in a larger spatiotemporal context, we compared our results for C. sociabilis to genetic data from additional modern and ancient populations of this species. These comparisons, combined with Bayesian serial coalescent modeling, suggest that post-eruption gene flow from nearby populations represents the most probable explanation for the apparent increase in post-eruption microsatellite diversity in C. sociabilis. Thus, detailed comparisons of pre- and post-eruption populations provide important insights into not only the genetic consequences of a natural catastrophic event, but also the demographic processes by which these changes in genetic diversity likely occurred.

Agricultural ecosystems are spatially and temporally dynamic systems that support wildlife populations in addition to food production for humans. The composition and configuration of land cover within agricultural systems, which often varies seasonally or annually, can have profound impacts on biodiversity. Specifically, landscape structure can influence animal dispersal and distribution. Depending on species-specific ecology, dispersal may be restricted, resulting in smaller, reproductively isolated populations. Few studies have characterized the spatial genetic structure of small mammal species in agricultural landscapes, despite their importance to crop pest management and food webs within agroecosystems. We characterized the spatial genetic structure of 2 co-distributed Peromyscus species (Peromyscus leucopus and Peromyscus maniculatus bairdii), and quantified relationships between spatial genetic structure based on interindividual relatedness resolved from 10 microsatellite loci, and landscape features hypothesized to influence dispersal. We found significant spatial autocorrelation in interindividual relatedness over interindividual distances of 1,800 m for P. leucopus and 300 m for P. maniculatus bairdii. We also identified distinct genetic clusters of interbreeding individuals for both species. Spatial genetic structure of P. leucopus was significantly related to the distribution of roads, indicating that highly fragmented landscapes could negatively affect dispersal and gene flow. Given the large and growing footprint of agriculture globally, it is important that studies of the effects that landscape features have on dispersal of wildlife species include human-dominated landscapes.

Microhabitat conditions affect foraging by small mammals. We investigated the effect of vegetation (vertical cover, coarse woody debris, size of trees) and illumination (cloud cover, lunar illumination) and their interactions on patch use and foraging by white-footed mice (Peromyscus leucopus) in deciduous forests in southwestern Ohio. We positioned feeding trays containing sunflower seeds mixed into sand with 1 seed placed on top of the sand on 5 grids during summer 2010 to measure patch use (removal of seed on top of the sand) and foraging intensity as GUD (giving-up density measured as proportion of seeds eaten). We used generalized linear mixed-effects models to determine how vegetation and illumination affected patch use and foraging. Patch use increased with increasing low vertical cover (LVC) and decreased with increasing lunar illumination likely because of a perception of risk of predation. If mice remained in a resource patch, foraging was explained by a more complex interaction between LVC, moon, and cloudiness. Little foraging occurred when LVC was low. At moderate levels of LVC, foraging decreased with increased lunar illumination, but increased when increased cloud cover decreased lunar illumination. For high levels of LVC, foraging increased on cloudy, dark nights and also on bright, cloudless nights. Our results differ from other foraging studies that examined only the effect of a single variable on foraging. We determined not only that different factors affect patch use and foraging, but also that foraging was affected by the interaction of LVC, lunar illumination, and cloud cover. Our results indicate that factors affecting habitats used (sensu lato) by white-footed mice differ from the broader factors that affect foraging decisions. Our results also may explain disparities of previous studies of foraging by white-footed mice that examined the effect of light levels or vegetative cover without considering their interactive effects.

Constructing water developments to support anthropogenic activities and particular fauna is pervasive across many arid regions of the globe. Despite their prevalence and a predicted increase as a management and conservation tool, water developments may have complex and unanticipated impacts on wildlife. For example, the addition of water developments to the Great Basin Desert in the western United States may have indirectly contributed to a decrease in distribution and abundance of kit foxes (Vulpes macrotis). From 2010 to 2013, we examined survival, relative abundance, and habitat characteristics of kit foxes in relation to water developments on the U.S. Army Dugway Proving Ground, Utah, using a before-after control-impact design. We collected 2 years of baseline data prior to reducing availability of water and continued data collection for another 2 years after removal of water on one-half of the study area. We found no evidence that removing water influenced survival or abundance of kit foxes. In addition, we found areas associated with the majority of water developments differed from current kit fox territories in elevation, soil type, and dominant cover type; historical use by kit foxes of areas associated with water developments is largely unknown. One explanation for our inability to find support for a water effect is that observed changes in the kit fox population and canid community in the Great Basin are attributable to changes in coyote management practices that temporally coincided with, but were largely unrelated to increases in water availability.

Long-distance vocal communication exists in many group-living carnivores. Understanding its behavioral and ecological significance suffers from few quantitative studies in undisturbed, wild populations. In Yellowstone National Park, Wyoming, United States, we examined seasonal changes in occurrence of wolf howls and howling replies based on more than 11,000 unsolicited howls given over a 10-year period. Howling was 5-fold most frequent in the pre-breeding and breeding seasons. Pack howls primarily, but also single howls, were most common during these seasons. Answers during these seasons were predominately interpack howls. These howling peaks correlated with elevations in estradiol, testosterone, and luteinizing hormone reported elsewhere. Following the breeding season, overall howling abruptly decreased through March and April, although howling at den sites was frequent, particularly in April and May. Howling frequency remained low all summer, during which time answers switched abruptly and almost exclusively from interpack to intrapack. Single howls stimulated distant pack members to answer with increasing frequency as the summer progressed. Although not independent, the frequency of both total howls and interpack howling rose throughout the fall. We relate these seasonal changes in total howling and interpack answers largely to breeding and spacing behavior in pre-breeding and breeding seasons, and intrapack answers to pack cohesion in other seasons. Because our results may reflect a high-density, unexploited wolf population, comparative studies under other conditions would be useful.

Fire shapes biome distribution and community composition worldwide, and is extensively used as a management tool in flammable landscapes. There is growing concern, however, that fire could increase the vulnerability of native fauna to invasive predators. We developed a conceptual model of the ways in which fire could influence predator–prey dynamics. Using a before–after, control–impact experiment, we then investigated the short-term effects of a prescribed fire on 2 globally significant invasive mesopredators (red fox, Vulpes vulpes, and feral cat, Felis catus) and their native mammalian prey in a fire-prone forest of southeastern Australia. We deployed motion-sensing cameras to assess species occurrence, collected predator scats to quantify diet and prey choice, and measured vegetation cover before and after fire. We examined the effects of the fire at the scale of the burn block (1,190 ha), and compared burned forest to unburned refuges. Pre-fire, invasive predators and large native herbivores were more likely to occur at sites with an open understory, whereas the occurrence of most small-and medium-sized native mammals was positively associated with understory cover. Fire reduced understory cover by more than 80%, and resulted in a 5-fold increase in the occurrence of invasive predators. Concurrently, relative consumption of medium-sized native mammals by foxes doubled, and selection of long-nosed bandicoots (Perameles nasuta) and short-beaked echidnas (Tachyglossus aculeatus) by foxes increased. Occurrence of bush rats (Rattus fuscipes) declined. It was unclear if fire also affected the occurrence of bandicoots or echidnas, as changes coincided with normal seasonal variations. Overall, prescribed fire promoted invasive predators, while disadvantaging their medium-sized native mammalian prey. Further replication and longer-term experiments are needed before these findings can be generalized. Nonetheless, such interactions could pose a serious threat to vulnerable species such as critical weight range mammals. Integrated invasive predator and fire management are recommended to improve biodiversity conservation in flammable ecosystems.

The temporal niche has received less attention than the spatial niche in ecological research on free-ranging animals. Most studies that have examined the effect of season on the diel activity patterns of small mammals have been conducted in temperate climates where daily temperatures and day length are important predictors of activity. Extremely seasonal rainfall in northern Australia possibly exerts a strong influence on mammalian activity due to the influx of food resources. Using camera traps set over a 3-year period, we documented the diel activity patterns of 5 species of small mammals co-occurring on Groote Eylandt, in the wet-dry tropics of northern Australia. All species were strictly nocturnal but some responded differently to the effect of season. The northern quoll (Dasyurus hallucatus) displayed a bimodal activity pattern that did not differ between the seasons. The northern brown bandicoot (Isoodon macrourus) displayed bimodal activity in the wet season and unimodal activity in the dry. The more sustained activity of I. macrourus in the dry season may be the result of this species utilizing more cellulose-rich food in times of lower insect abundance, whereas D. hallucatus possibly exhibits lower dietary plasticity. The northern hopping-mouse (Notomys aquilo) was consistently active throughout the night in both seasons. Conversely, the delicate mouse (Pseudomys delicatulus) showed great plasticity in its nocturnal activity which altered significantly depending on both season and habitat. The disparity in activity pattern between these 2 rodents possibly reflects differences in predation risks. The grassland melomys (Melomysburtoni) was recorded only during the dry season in coastal grassland habitat, when its activity peaked sharply after nightfall. Our study highlights the interspecific variation in small mammal activity between the wet and dry seasons in northern Australia, which may be explained by differences in diet, habitat use, and predation risk in these species.

The endangered northern quoll (Dasyurus hallucatus) is a predatory marsupial with a wide and disjointed distribution across northern Australia. The disjunct Pilbara population occurs in a uniquely arid area, and faces different threatening processes to populations elsewhere. To better understand the ecology of this small carnivore, we undertook a dietary analysis of 498 scats collected across ∼100,000 km². We calculated dietary composition and niche breadth and modeled these against biogeophysical factors (latitude, longitude, rainfall, elevation, and distance to coast) for 10 study landscapes. We also conducted pairwise comparisons of diet groups to evaluate regional dietary differences. Quolls were highly omnivorous, consuming at least 23 species of vertebrates (mammals, birds, reptiles, frogs), as well as arthropods, molluscs, fruit, and carrion. Diet varied widely across the region, with up to 3-fold differences in dietary niche breadth between study landscapes. We found few clear environmental drivers of the diet of D. hallucatus. The most frequently consumed food type was insects, but their occurrence in diets decreased as that of rodents and vegetation increased, indicating potential dietary preferences. The broad and variable diet of D. hallucatus indicates opportunism similar to that of other small carnivores. Given this broad dietary niche, conservation managers will need a priori knowledge of local prey abundance if they are to accurately predict the composition of D. hallucatus diets.

Many mammals use heterothermy to meet challenges of reduced food availability and low temperatures, but little is known about the prevalence of heterothermy in wild mesocarnivores. We monitored body temperature (T_b) in free-living striped skunks (Mephitis mephitis) through winter 2015–2016 in suburban Flagstaff, Arizona, a high-elevation site that experiences temperate winters. Subcutaneous T_b and heterothermy index (HI) were significantly affected by ambient temperature, and varied significantly across 7 skunks in midwinter. Twenty-one of 36 (58%) unique diurnal dens used by skunks were associated with human structures, and although females were found in dens under houses more than expected compared to males, we found little evidence that skunks selected dens where they could access anthropogenic heat sources. This is the 1st study to document T_b variation over winter in free-living striped skunks. Our results are consistent with 2 previous studies of captive skunks in documenting considerable variation among individuals in the extent of heterothermy. If reduced T_b during heterothermy alters rate of viral replication, variation among individual skunks could have implications for the maintenance and spread of diseases like rabies.

Belugas are thought to exhibit seasonal variation in testes size, but a temporal gap in postmortem sampling of wild belugas has precluded a description of the occurrence or the extent of this seasonal variation. This study aimed to utilize longitudinal monitoring of belugas in aquaria with known siring histories to assess seasonal variation in testes size, and its association with circulating testosterone concentration and testicular tissue density. Testes volume was estimated using linear measurements obtained via ultrasonography. Testicular tissue density was assessed by measuring the pixel intensity (PI) of ultrasound images of the testis. Five adult males, including 4 proven sires, were monitored for at least 1 continuous year; 2 of the males were monitored for > 2 years. A total of 154 ultrasound examinations (including 71 suitable for PI measurements) and 119 blood samples were available for analysis. Significant seasonal variation in testes volume, circulating testosterone concentration, and testicular PI were observed, with peak activity occurring between January and April. Seasonality of testicular volume was best described by a cubic function, while seasonal variations in testosterone and PI were best described by quadratic functions. Individuals differed significantly in both testes size and rate of change. On average, testes size increased by 60% from minimum to maximum values. These results are consistent with observations of reproductive seasonality both in the wild and in aquaria, and suggest a relatively low demand for sperm in this species that is consistent with their classification as induced ovulators.

Due to significant population declines in the 1970s and 1980s, Steller sea lions (Eumetopias jubatus) were listed as threatened under the U.S. Endangered Species Act in 1990, and subsequently partitioned in 1997 into an endangered western stock and a threatened eastern stock. We estimated survival rates from a mark-recapture study of 7 eastern stock cohorts marked as pups in California and Oregon from 2001 to 2009 (n = 1,154 pups) and resighted range-wide from 2002 to 2013. First-year survival rates were among the lowest found for Steller sea lions thus far, averaging 0.46 (range 0.21–0.72) for females and 0.44 (0.21–0.68) for males; yearling survival rates, however, were among the highest, averaging 0.85 for females and 0.81 for males. Low pup and high yearling rates offset each other, however, so that cumulative survival rates to age 4, averaging 0.33 for females and 0.27 for males, were similar to those found in studies from Alaska and Russia. While range-limit effects and environmental variation may be related to the low and variable pup survival rates we found, populations in Oregon and California nonetheless continued to grow, which contributed to delisting of the eastern stock in 2013. Continued monitoring and incorporation of new information on vital rates into regional population models will help inform post-delisting monitoring for the eastern stock of Steller sea lions.

The Eurasian beaver (Castor fiber L.) is the largest free-living rodent in Eurasia. Beavers show seasonal patterns of reproduction (long-day breeders), stress reactions, and feeding behavior. These phenomena are associated with the function of hormonal regulatory axes: the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG). In mammals, the above processes are also controlled by orexins (OXA and OXB), neuropeptides derived from the same precursor—prepro-orexin (PPO). We hypothesized that in beavers PPO gene expression in tissues creating the HPA-HPG axes and plasma orexin concentrations differ between seasons and sexes. PPO transcript and PPO and orexin proteins were noted in the mediobasal hypothalamus (MBH), pituitary, adrenals, and gonads in April (“breeding, pregnancy”), July (“post-breeding”), and November (“pre-breeding”). In the MBH, seasonal, but not sex-dependent variations were observed in PPO gene expression; however, the transcript content increased in females in July. An interaction between season and sex was noted in the pituitary: PPO gene expression decreased in males in April. The PPO mRNA concentration in adrenals varied between seasons and sexes. Additionally, an interaction between these factors occurred and the highest PPO gene expression was noted in females in April. In the gonads, PPO mRNA levels changed dependent on season, and an interaction between season and sex was found. The PPO transcript increased in November in the testes. Seasonal variations and an interaction between season and sex were observed in plasma OXA. The highest concentration of OXA was noted in July (males) and in November (females). In beavers, PPO gene expression and plasma OXA concentration varied depending on season and these changes were modified by sex. Our results imply that orexin peptides are involved in the regulation of circannual changes of reproductive activity in beavers and seem to be associated with seasonal fluctuations in glucocorticoid secretion and stress reactions.