Genetic architecture and evolution of color variation in American black bears

Color variation is a frequent evolutionary substrate for camouflage in small mammals, but the underlying genetics and evolutionary forces that drive color variation in natural populations of large mammals are mostly unexplained. The American black bear, Ursus americanus (U. americanus), exhibits a range of colors including the cinnamon morph, which has a similar color to the brown bear, U. arctos, and is found at high frequency in the American southwest. Reflectance and chemical melanin measurements showed little distinction between U. arctos and cinnamon U. americanus individuals. We used a genome-wide association for hair color as a quantitative trait in 151 U. americanus individuals and identified a single major locus (p < 10-13). Additional genomic and functional studies identified a missense alteration (R153C) in Tyrosinase-related protein 1 (TYRP1) that likely affects binding of the zinc cofactor, impairs protein localization, and results in decreased pigment production. Population genetic analyses and demographic modeling indicated that the R153C variant arose 9.36 kya in a southwestern population where it likely provided a selective advantage, spreading both northwards and eastwards by gene flow. A different TYRP1 allele, R114C, contributes to the characteristic brown color of U. arctos but is not fixed across the range.

An engineering perspective on the development and evolution of implantable cardiac monitors in free-living animals

The latest technologies associated with implantable physiological monitoring devices can record multiple channels of data (including: heart rates and rhythms, activity, temperature, impedance and posture), and coupled with powerful software applications, have provided novel insights into the physiology of animals in the wild. This perspective details past challenges and lessons learned from the uses and developments of implanted biologgers designed for human clinical application in our research on free-ranging American black bears (Ursus americanus). In addition, we reference other research by colleagues and collaborators who have leveraged these devices in their work, including: brown bears (Ursus arctos), grey wolves (Canis lupus), moose (Alces alces), maned wolves (Chrysocyon brachyurus) and southern elephant seals (Mirounga leonina). We also discuss the potentials for applications of such devices across a range of other species. To date, the devices described have been used in fifteen different wild species, with publications pending in many instances. We have focused our physiological research on the analyses of heart rates and rhythms and thus special attention will be paid to this topic. We then discuss some major expected step changes such as improvements in sensing algorithms, data storage, and the incorporation of next-generation short-range wireless telemetry. The latter provides new avenues for data transfer, and when combined with cloud-based computing, it not only provides means for big data storage but also the ability to readily leverage high-performance computing platforms using artificial intelligence and machine learning algorithms. These advances will dramatically increase both data quantity and quality and will facilitate the development of automated recognition of extreme physiological events or key behaviours of interest in a broad array of environments, thus further aiding wildlife monitoring and management.

This article is part of the theme issue ‘Measuring physiology in free-living animals (Part I)’.

Bears habituate to the repeated exposure of a novel stimulus, unmanned aircraft systems

Unmanned aircraft systems (UAS; i.e. 'drones') provide new opportunities for data collection in ecology, wildlife biology and conservation. Yet, several studies have documented behavioral or physiological responses to close-proximity UAS flights. We experimentally tested whether American black bears (Ursus americanus) habituate to repeated UAS exposure and whether tolerance levels persist during an extended period without UAS flights. Using implanted cardiac biologgers, we measured heart rate (HR) of five captive bears before and after the first of five flights each day. Spikes in HR, a measure of stress, diminished across the five flights within each day and over the course of 4 weeks of twice-weekly exposure. We halted flights for 118 days, and when we resumed, HR responses were similar to that at the end of the previous trials. Our findings highlight the capacity of a large mammal to become and remain habituated to a novel anthropogenic stimulus in a relatively short time (3-4 weeks). However, such habituation to mechanical noises may reduce their wariness of other human threats. Also, whereas cardiac effects diminished, frequent UAS disturbances may have other chronic physiological effects that were not measured. We caution that the rate of habituation may differ between wild and captive animals: while the captive bears displayed large initial spikes in HR change (albeit not as large as wild bears), these animals were accustomed to regular exposure to humans and mechanical noises that may have hastened habituation to the UAS.

Six Years in the Life of a Mother Bear - The Longest Continuous Heart Rate Recordings from a Free-Ranging Mammal

Physiological monitoring of free-ranging wild animals is providing new insights into their adaptations to a changing environment. American black bears (Ursus americanus) are highly adaptable mammals, spending up to half the year hibernating, and the remainder of the year attempting to gain weight on a landscape with foods that vary seasonally and year to year. We recorded heart rate (HR) and corresponding activity of an adult female black bear over the course of six years, using an implanted monitor. Despite yearly differences in food, and an every-other year reproductive cycle, this bear exhibited remarkable consistency in HR and activity. HR increased for 12 weeks in spring, from minimal hibernation levels (mean 20–25 beats/minute [bpm]; min 10 bpm) to summer active levels (July daytime: mean 95 bpm). Timing was delayed following one cold winter. In August the bear switched from primarily diurnal to nocturnal, coincident with the availability of baits set by legal hunters. Activity in autumn was higher when the bear was with cubs. Birthing of cubs in January was identified by a transient increase in HR and activity. Long-term physiological and behavioral monitoring is valuable for understanding adaptations of free-ranging animals to climate change, food availability, and human-related stressors.

Blood clotting behavior is innately modulated in Ursus americanus during early and late denning relative to summer months

Remarkably, American black bears (Ursus americanus) are capable of varying their heart rates to coincide with their breathing, creating pauses of 30 s or more, yet they do not appear to suffer from embolic events. We evaluated some features of the clotting cascade of black bears, providing novel insights into the underlying mechanisms they evoke for embolic protection during hibernation. We measured activated clotting time, prothrombin time and activated partial thromboplastin time during early denning (December), late denning (March) and summer (August). Activated clotting time during early hibernation was ∼3 times longer than that observed among non-hibernating animals. Clotting time was reduced later in hibernation, when bears were within ∼1 month of emerging from dens. Prothrombin time was similar for each seasonal time point, whereas activated partial thromboplastin time was highest during early denning and decreased during late denning and summer. We also examined D-dimer concentration to assess whether the bears were likely to have experienced embolic events. None of the non-parturient bears exceeded a D-dimer concentration of 250 ng ml^-1 (considered the clinical threshold for embolism in mammals). Our findings suggest there is unique expression of the clotting cascade in American black bears during hibernation, in which extrinsic pathways are maintained but intrinsic pathways are suppressed. This was evaluated by a significant difference between the activated clotting time and activated partial thromboplastin time during the denning and non-denning periods. These changes are likely adaptive, to avoid clotting events during states of immobilization and/or periods of asystole. However, an intact extrinsic pathway allows for healing of external injuries and/or foreign body responses.

Are American black bears in an agricultural landscape being sustained by crops?

Human-altered landscapes are thought to reduce habitat quality for many forest-dependent species, but some omnivorous, opportunist species take advantage of human-related food sources, such as garbage and crops. It is unknown, however, whether anthropogenic foods can sustain populations in areas with relatively little natural habitat. We studied (2007–2012) a population of American black bears ( Ursus americanus ) at the western periphery of their range in Minnesota, in a landscape that was heavily impacted by agriculture (~50%). We estimated the dietary contributions of corn and sunflowers (2–4% of the landscape) versus seasonally available natural foods (spring vegetation, ants, deer, fruit, and nuts) with stable isotope analyses (δ 13 C and δ 15 N) of 110 hair samples from 51 bears. We identified associations between diet and sex, age, body size and condition, reproductive status, space use, habitat connectivity, and natural food abundance. At the population level, adult males and adult females without cubs consumed considerable crops in fall (95% credible intervals: males = 19–46% of diet, females = 10–40%), but females with cubs and juvenile bears rarely consumed crops. Individual estimates of crop consumption were positively correlated with the proportion of GPS-collar locations in crop fields. Females, but not males, decreased crop consumption in years with high availability of natural fall foods. Further, the degree of crop consumption was more closely tied to local crop availability and landscape composition in females than in males. Weight and fat were positively correlated with crop use for both sexes, and males’ use of crops also increased with their physical stature, suggesting that crops provided substantial caloric benefits to bears and that social dominance may have influenced foraging decisions. However, a large segment of this bear population (44% of sampled bear–years) made little use of crops, and crops accounted for more than half the fall diet for only 14% of the population. Whereas some bears clearly benefited from consumption of crops, we conclude that a population of bears could be sustained in this largely agricultural region even without crops as a food source.

Bears Show a Physiological but Limited Behavioral Response to Unmanned Aerial Vehicles

Unmanned aerial vehicles (UAVs) have the potential to revolutionize the way research is conducted in many scientific fields. UAVs can access remote or difficult terrain, collect large amounts of data for lower cost than traditional aerial methods, and facilitate observations of species that are wary of human presence. Currently, despite large regulatory hurdles, UAVs are being deployed by researchers and conservationists to monitor threats to biodiversity, collect frequent aerial imagery, estimate population abundance, and deter poaching. Studies have examined the behavioral responses of wildlife to aircraft (including UAVs), but with the widespread increase in UAV flights, it is critical to understand whether UAVs act as stressors to wildlife and to quantify that impact. Biologger technology allows for the remote monitoring of stress responses in free-roaming individuals, and when linked to locational information, it can be used to determine events or components of an animal's environment that elicit a physiological response not apparent based on behavior alone. We assessed effects of UAV flights on movements and heart rate responses of free-roaming American black bears. We observed consistently strong physiological responses but infrequent behavioral changes. All bears, including an individual denned for hibernation, responded to UAV flights with elevated heart rates, rising as much as 123 beats per minute above the pre-flight baseline. It is important to consider the additional stress on wildlife from UAV flights when developing regulations and best scientific practices.

Big data in wildlife research: remote web-based monitoring of hibernating black bears

Background

Numerous innovations for the management and collection of “big data” have arisen in the field of medicine, including implantable computers and sensors, wireless data transmission, and web-based repositories for collecting and organizing information. Recently, human clinical devices have been deployed in captive and free-ranging wildlife to aid in the characterization of both normal physiology and the interaction of animals with their environment, including reactions to humans. Although these devices have had a significant impact on the types and quantities of information that can be collected, their utility has been limited by internal memory capacities, the efforts required to extract and analyze information, and by the necessity to handle the animals in order to retrieve stored data.

Results

We surgically implanted miniaturized cardiac monitors (1.2 cc, Reveal LINQ™, Medtronic Inc.), a newly developed human clinical system, into hibernating wild American black bears (N = 6). These devices include wireless capabilities, which enabled frequent transmissions of detailed physiological data from bears in their remote den sites to a web-based data storage and management system. Solar and battery powered telemetry stations transmitted detailed physiological data over the cellular network during the winter months. The system provided the transfer of large quantities of data in near-real time. Observations included changes in heart rhythms associated with birthing and caring for cubs, and in all bears, long periods without heart beats (up to 16 seconds) occurred during each respiratory cycle.

Conclusions

For the first time, detailed physiological data were successfully transferred from an animal in the wild to a web-based data collection and management system, overcoming previous limitations on the quantities of data that could be transferred. The system provides an opportunity to detect unusual events as they are occurring, enabling investigation of the animal and site shortly afterwards. Although the current study was limited to bears in winter dens, we anticipate that future systems will transmit data from implantable monitors to wearable transmitters, allowing for big data transfer on non-stationary animals.

Fellatio in captive brown bears: evidence of long-term effects of suckling deprivation?

Sexually stimulating behaviors that are not linked to reproduction are rare among non-human (especially non-primate) mammals. Such behaviors may have a function in the hierarchy of social species. In solitary species, such behaviors are more enigmatic, and possibly indicative of something abnormal. Here, we report on a case of two male brown bears, raised in captivity since being orphaned as cubs, which engaged in recurrent fellatio multiple times per day until at least 10 years old. The roles of provider and receiver in the act remained unchanged, and the behavior itself became highly ritualized. The provider always initiated the contact involving vigorous penile sucking that appeared to result in ejaculation. We suggest that the behavior began as a result of early deprivation of maternal suckling, and persisted through life, possibly because it remained satisfying for both individuals. This constitutes the first descriptive report of fellatio in bears, and suggests that some bears may suffer lifelong behavioral consequences from being orphaned at an early age.

Prolonged recovery of sea otters from the Exxon Valdez oil spill? A re-examination of the evidence

Sea otters (Enhydra lutris) suffered major mortality after the Exxon Valdez oil spill in Prince William Sound, Alaska, 1989. We evaluate the contention that their recovery spanned over two decades. A model based on the otter age-at-death distribution suggested a large, spill-related population sink, but this has never been found, and other model predictions failed to match empirical data. Studies focused on a previously-oiled area where otter numbers (~80) stagnated post-spill; nevertheless, post-spill abundance exceeded the most recent pre-spill count, and population trends paralleled an adjacent, unoiled-lightly-oiled area. Some investigators posited that otters suffered chronic effects by digging up buried oil residues while foraging, but an ecological risk assessment indicated that exposure levels via this pathway were well below thresholds for toxicological effects. Significant confounding factors, including killer whale predation, subsistence harvests, human disturbances, and environmental regime shifts made it impossible to judge recovery at such a small scale.

Wound healing during hibernation by black bears (Ursus americanus) in the wild: elicitation of reduced scar formation

Even mildly hypothermic body or limb temperatures can retard healing processes in mammals. Despite this, we observed that hibernating American black bears (Ursus americanus Pallas, 1780) elicit profound abilities in mounting inflammatory responses to infection and/or foreign bodies. In addition, they resolve injuries during hibernation while maintaining mildly hypothermic states (30-35 °C) and without eating, drinking, urinating or defecating. We describe experimental studies on free-ranging bears that document their abilities to completely resolve cutaneous cuts and punctures incurred during or prior to hibernation. We induced small, full-thickness cutaneous wounds (biopsies or incisions) during early denning, and re-biopsied sites 2-3 months later (near the end of denning). Routine histological methods were used to characterize these skin samples. All biopsied sites with respect to secondary intention (open circular biopsies) and primary intention (sutured sites) healed, with evidence of initial eschar (scab) formation, completeness of healed epidermis and dermal layers, dyskeratosis (inclusion cysts), and abilities to produce hair follicles. These healing abilities of hibernating black bears are a clear survival advantage to animals injured before or during denning. Bears are known to have elevated levels of hibernation induction trigger (delta-opioid receptor agonist) and ursodeoxycholic acid (major bile acid within plasma, mostly conjugated with taurine) during hibernation, which may relate to these wound-healing abilities. Further research as to the underlying mechanisms of wound healing during hibernation could have applications in human medicine. Unique approaches may be found to improve healing for malnourished, hypothermic, diabetic and elderly patients or to reduce scarring associated with burns and traumatic injuries.

Seasonal regulation of the growth hormone-insulin-like growth factor-I axis in the American black bear (Ursus americanus)

The American black bear maintains lean body mass for months without food during winter denning. We asked whether changes in the growth hormone/insulin-like growth factor-I (GH-IGF-I) axis may contribute to this remarkable adaptation to starvation. Serum IGF-I levels were measured by radioimmunoassay, and IGF-binding proteins (IGFBPs) were analyzed by ligand blotting. Initial studies in bears living in the wild showed that IGF-I levels are highest in summer and lowest in early winter denning. Detailed studies in captive bears showed that IGF-I levels decline in autumn when bears are hyperphagic, continue to decline in early denning, and later rise above predenning levels despite continued starvation in the den. IGFBP-2 increased and IGFBP-3 decreased in early denning, and these changes were also reversed in later denning. Treatment with GH (0.1 mg·kg(-1)·day(-1) × 6 days) during early denning increased serum levels of IGF-I and IGFBP-3 and lowered levels of IGFBP-2, indicating that denning bears remain responsive to GH. GH treatment lowered blood urea nitrogen levels, reflecting effects on protein metabolism. GH also accelerated weight loss and markedly increased serum levels of free fatty acids and β-hydroxybutyrate, resulting in a ketoacidosis (bicarbonate decreased to 15 meq/l), which was reversed when GH was withdrawn. These results demonstrate seasonal regulation of GH/IGF-I axis activity in black bears. Diminished GH activity may promote fat storage in autumn in preparation for denning and prevent excessive mobilization and premature exhaustion of fat stores in early denning, whereas restoration of GH/IGF activity in later denning may prepare the bear for normal activity outside the den.

Monitoring the wild black bear's reaction to human and environmental stressors

BACKGROUND

Bears are among the most physiologically remarkable mammals. They spend half their life in an active state and the other half in a state of dormancy without food or water, and without urinating, defecating, or physical activity, yet can rouse and defend themselves when disturbed. Although important data have been obtained in both captive and wild bears, long-term physiological monitoring of bears has not been possible until the recent advancement of implantable devices.

RESULTS

Insertable cardiac monitors that were developed for use in human heart patients (Reveal® XT, Medtronic, Inc) were implanted in 15 hibernating bears. Data were recovered from 8, including 2 that were legally shot by hunters. Devices recorded low heart rates (pauses of over 14 seconds) and low respiration rates (1.5 breaths/min) during hibernation, dramatic respiratory sinus arrhythmias in the fall and winter months, and elevated heart rates in summer (up to 214 beats/min (bpm)) and during interactions with hunters (exceeding 250 bpm). The devices documented the first and last day of denning, a period of quiescence in two parturient females after birthing, and extraordinary variation in the amount of activity/day, ranging from 0 (winter) to 1084 minutes (summer). Data showed a transition toward greater nocturnal activity in the fall, preceding hibernation. The data-loggers also provided evidence of the physiological and behavioral responses of bears to our den visits to retrieve the data.

CONCLUSIONS

Annual variations in heart rate and activity have been documented for the first time in wild black bears. This technique has broad applications to wildlife management and physiological research, enabling the impact of environmental stressors from humans, changing seasons, climate change, social interactions and predation to be directly monitored over multiple years.

The shared preference niche of sympatric Asiatic black bears and sun bears in a tropical forest mosaic

Background

Ecologically similar species often coexist by partitioning use of habitats or resources. Such partitioning can occur through divergent or shared niches. We investigated overlap in habitat use and spatial co-occurrence by sympatric Asiatic black bears and sun bears in three habitats in Thailand, and thereby assessed which niche model best accounts for their coexistence.

Methods/Principal Findings

We used density of species-specific signs to assess habitat use. Signs of both bear species occurred in all three habitats, and on >60% of sampling transects. Both species fed mostly on fruit; insect feeding signs were uncommon, and were mostly from sun bears. Significant differences in habitat use occurred only in montane forest, the habitat in which fruit was most abundant; incidence of black bear sign there was six times higher than that of sun bears. Habitat use was similar between the two species in the other habitats, which comprised 85% of the area. Of 10 habitat attributes examined, fruiting tree density was the best predictor of occurrence for both species. Models that included interspecific competition (fresh foraging activity of the other species) were less supported than the top models without competition.

Conclusions/Significance

Bear species co-occurrence at both coarse and fine spatial scales and use of the same resources (fruit trees) indicated common niche preferences. However, their habitat use differed in ways expected from their physical differences: larger black bears dominated in the most fruit-rich habitat, and smaller sun bears used less-preferred insects. These results indicate broadly overlapping fundamental niches combined with asymmetric competition—features consistent with the concept of shared preference niches. This model of the niche has received little attention in ecology, but appears to be relatively common in nature.

The impact of conservation on the status of the world's vertebrates

Using data for 25,780 species categorized on the International Union for Conservation of Nature Red List, we present an assessment of the status of the world's vertebrates. One-fifth of species are classified as Threatened, and we show that this figure is increasing: On average, 52 species of mammals, birds, and amphibians move one category closer to extinction each year. However, this overall pattern conceals the impact of conservation successes, and we show that the rate of deterioration would have been at least one-fifth again as much in the absence of these. Nonetheless, current conservation efforts remain insufficient to offset the main drivers of biodiversity loss in these groups: agricultural expansion, logging, overexploitation, and invasive alien species.

Integrated population modeling of black bears in Minnesota: implications for monitoring and management

Background

Wildlife populations are difficult to monitor directly because of costs and logistical challenges associated with collecting informative abundance data from live animals. By contrast, data on harvested individuals (e.g., age and sex) are often readily available. Increasingly, integrated population models are used for natural resource management because they synthesize various relevant data into a single analysis.

Methodology/Principal Findings

We investigated the performance of integrated population models applied to black bears (Ursus americanus) in Minnesota, USA. Models were constructed using sex-specific age-at-harvest matrices (1980–2008), data on hunting effort and natural food supplies (which affects hunting success), and statewide mark–recapture estimates of abundance (1991, 1997, 2002). We compared this approach to Downing reconstruction, a commonly used population monitoring method that utilizes only age-at-harvest data. We first conducted a large-scale simulation study, in which our integrated models provided more accurate estimates of population trends than did Downing reconstruction. Estimates of trends were robust to various forms of model misspecification, including incorrectly specified cub and yearling survival parameters, age-related reporting biases in harvest data, and unmodeled temporal variability in survival and harvest rates. When applied to actual data on Minnesota black bears, the model predicted that harvest rates were negatively correlated with food availability and positively correlated with hunting effort, consistent with independent telemetry data. With no direct data on fertility, the model also correctly predicted 2-point cycles in cub production. Model-derived estimates of abundance for the most recent years provided a reasonable match to an empirical population estimate obtained after modeling efforts were completed.

Conclusions/Significance

Integrated population modeling provided a reasonable framework for synthesizing age-at-harvest data, periodic large-scale abundance estimates, and measured covariates thought to affect harvest rates of black bears in Minnesota. Collection and analysis of these data appear to form the basis of a robust and viable population monitoring program.

A Quantitative Ecological Risk Assessment of the Toxicological Risks from Exxon Valdez Subsurface Oil Residues to Sea Otters at Northern Knight Island, Prince William Sound, Alaska

A comprehensive, quantitative risk assessment is presented of the toxicological risks from buried Exxon Valdez subsurface oil residues (SSOR) to a subpopulation of sea otters (Enhydra lutris) at Northern Knight Island (NKI) in Prince William Sound, Alaska, as it has been asserted that this subpopulation of sea otters may be experiencing adverse effects from the SSOR. The central questions in this study are: could the risk to NKI sea otters from exposure to polycyclic aromatic hydrocarbons (PAHs) in SSOR, as characterized in 2001-2003, result in individual health effects, and, if so, could that exposure cause subpopulation-level effects? We follow the U.S. Environmental Protection Agency (USEPA) risk paradigm by: (a) identifying potential routes of exposure to PAHs from SSOR; (b) developing a quantitative simulation model of exposures using the best available scientific information; (c) developing scenarios based on calculated probabilities of sea otter exposures to SSOR; (d) simulating exposures for 500,000 modeled sea otters and extracting the 99.9% quantile most highly exposed individuals; and (e) comparing projected exposures to chronic toxicity reference values. Results indicate that, even under conservative assumptions in the model, maximum-exposed sea otters would not receive a dose of PAHs sufficient to cause any health effects; consequently, no plausible toxicological risk exists from SSOR to the sea otter subpopulation at NKI.

Extreme respiratory sinus arrhythmia enables overwintering black bear survival--physiological insights and applications to human medicine

American black bears survive winter months without food and water while in a mildly hypothermic, hypometabolic, and inactive state, yet they appear to be able to return to near-normal systemic function within minutes of arousal. This study's goal was to characterize the cardiovascular performance of overwintering black bears and elicit the underlying mechanisms enabling survival. Mid-winter cardiac electrophysiology was assessed in four wild black bears using implanted data recorders. Paired data from early and late winter were collected from 37 wild bears, which were anesthetized and temporarily removed from their dens to record cardiac electrophysiological parameters (12-lead electrocardiograms) and cardiac dimensional changes (echocardiography). Left ventricular thickness, primary cardiac electrophysiological parameters, and cardiovascular response to threats ("fight or flight" response) were preserved throughout winter. Dramatic respiratory sinus arrhythmias were recorded (cardiac cycle length variations up to 865%) with long sinus pauses between breaths (up to 13 s). The accelerated heart rate during breathing efficiently transports oxygen, with the heart "resting" between breaths to minimize energy usage. This adaptive cardiac physiology may have broad implications for human medicine.

Comment on "On the regulation of populations of mammals, birds, fish, and insects" IV

Sibly et al.'s (Reports, 22 July 2005, p. 607) contention that density dependence acts strongly on low-density animal populations irrespective of body size contradicts many long-term studies of large mammals. Their findings were distorted by harvest records, which may poorly reflect population trend. Omitting unreliable data, their massive data set is reduced to only one case for large mammals.

Plasma levels of ursodeoxycholic acid in black bears, Ursus americanus: seasonal changes

To date, no other studies have examined the seasonal changes in circulating levels of various bile acids in the plasma of wild North American black bears, Ursus americanus. Using gas chromatography, bile acid concentrations were measured in plasma samples obtained during either early or late hibernation, and during summer active periods. Thus, specific compositional changes from individual animals were examined through a given year. Total bile acid concentrations in the plasma of these normal animals were found to range between 0.2 and 3.1 micromol/L (0.9 +/- 0.2 micromol/L, mean +/- SEM). Cholic, ursodeoxycholic and chenodeoxycholic acids were the major bile acid species identified. Ursodeoxycholic acid represented 28.0 +/- 2.6% of the total bile acid pool. Deoxycholic and lithocholic acids were found only in small amounts. In addition, total bile acid concentrations were lower in plasma samples obtained during hibernation compared with those obtained during summer active periods (0.6 +/- 0.1 and 1.2 +/- 0.4 micromol/L, respectively; p < 0.05). However, the relative proportion of ursodeoxycholic acid, was significantly greater in winter than in summer (31.5 +/- 3.2% and 22.2 +/- 4.5%, p < 0.05). Finally, taurine-conjugated bile acids were the predominant species in bear plasma, accounting for >67% of the total bile acids. These data demonstrate that ursodeoxycholic acid is a major bile acid in black bear plasma, mostly conjugated with taurine. Further, the finding of seasonal variation in plasma bile acid composition provides evidence to support the possible role that ursodeoxycholic acid may play in cellular protection in hibernating black bears.

Sociobiology of the myrmecophagous sloth bear in Nepal

Ursids have adapted to environments ranging from the tropics to the arctic, and although the family is noted for its omnivory, some species have specialized food habits. The sloth bear (Melursus ursinus) has specialized on insect prey, particularly termites and ants, and exhibits some characteristics and behaviors that are common among myrmecophagous mammals. We examined whether myrmecophagy has affected its sociobiology. During 1990-1994 we studied a high-density population of sloth bears in Royal Chitwan National Park, Nepal. We found extensive seasonal overlap among home ranges of adults of the same sex (>50%) and between subadults and adults of both sexes (>70%). Moreover, overlap zones between adjacent ranges were used in proportion to their area. This, and observations of unrelated bears feeding or traveling in proximity to one another (not at concentrated food sources), suggested a high degree of mutual tolerance in this population. However, subadults and females with young may have temporally avoided other bears by limiting their activity to daylight hours. Predators (which were chiefly nocturnal) may also have affected the activity patterns of these (the most vulnerable) bears, and were probably responsible for the females' habit of giving birth in an underground den, fasting for several weeks so as not to leave cubs unattended in the den, and carrying the cubs on their back for 6-7 months after leaving the den. The young left their mother at 1.5 or 2.5 years old (this varied by family) and remained together and (or) later rejoined a sibling or another subadult, possibly to form a coalition against either predators or older bears. We documented few mortalities and no permanent juvenile dispersal in this study, but we also found few subadults in our study area, which indicates undetected mortality or dispersal. We cannot discount the possibility that some aspects of the sociobiology of sloth bears (e.g., cub-carrying, mutual tolerance) are related to myrmecophagy, but the social system and life-history traits of this species seem to fit well within the range observed among other ursids.

Sex steroid and prolactin profiles in male American black bears (Ursus americanus) during denning

Serum sex steroid and prolactin profiles were examined in the male American black bear, Ursus americanus during denning. Sera collected in December and the following March from 8 denning male black bears in Minnesota, U.S.A. were assayed for testosterone, estradiol-17 beta and prolactin. Eight bears were confirmed to be the denning mode based on a serum urea to creatinine ratio less than 10. Serum testosterone concentrations tended to increase from December to the subsequent March whereas serum estradiol-17 beta concentrations tended to decrease during this period. There were few changes in serum prolactin concentrations between December and March. These findings suggest that spermatogenesis and testicular steroidogenesis initiated during denning may be influenced by changes in serum sex steroid concentrations in the American black bear.

Serum progesterone, oestradiol, luteinizing hormone and prolactin profiles in the female black bear (Ursus americanus)

Identifying steroid and pituitary hormone profiles in the female black bear (Ursus americanus) throughout pregnancy may provide a greater understanding of the reproductive cycle and indicate which hormones are required for implantation. Our objective was to assess endocrine activity in black bears oestrus onset, at oestrus, during pregnancy and after parturition. Serum samples were obtained from 12 captive, 16 uncollared and five radiocollared free-ranging female black bears from March through the end of December and assayed for serum progesterone, oestradiol, luteinizing hormone (LH) and prolactin (PRL). In captive bears, progesterone concentrations were low at days 0-10 after oestrus and increased significantly days 25-35 and 45-52 after oestrus. Oestradiol concentrations were high at oestrus (day 0) and days 4-10 after oestrus and then decreased days 25-35 and 45-52 after oestrus. LH concentrations were not significantly different throughout the sampling period. Changes in PRL concentrations pattern were similar to those of oestradiol, with elevated levels at oestrus and days 4-10 after oestrus, followed by a significant decrease 45-52 days after oestrus. In non-collared free-ranging bears, progesterone concentrations increased gradually after mating with a further significant increase in November-December. Oestradiol concentrations were highest in March (before mating) and in June (during mating) followed by a significant decrease in July (early delay period) and November-December (peri-implantation period). LH concentrations were low until November-December and then increased significantly. PRL concentrations were low in March (before mating), increased significantly during the mating season in June, decreased slightly in July, and were low in November-December (peri-implantation period). In radiocollared free-ranging bears, serum progesterone concentrations were elevated in pregnant bears in December and extremely low in lactating and non-lactating bears in March. Oestradiol levels were slightly higher in pregnant bears in December than in non-lactating or lactating bears in March. PRL concentrations were considerably higher in lactating bears in March than in pregnant bears in December. Our results suggest that: (1) serum progesterone concentrations are low, but detectable during the early delay implantation period and greatly elevated during the peri-implantation period; (2) serum oestradiol concentrations are elevated at oestrus and decline during the delay period; (3) LH may be involved in luteal activation; and (4) the decline of serum PRL concentrations during short days may be necessary for implantation to occur.

Reconstructing reproductive histories of black bears from the incremental layering in dental cementum

Known reproductive histories of female radio-collared black bears (Ursus americanus) in Minnesota were matched against the spacing of growth layers in stained thin sections of their teeth. Light-staining bands of cementum, deposited during the summer months, were relatively narrow during years when females were raising cubs. Because females in this study never successfully reared cubs in 2 consecutive years, narrow light bands were bordered by wider bands, causing the intervening dark-staining fall–winter annuli to appear paired. Adult males exhibited similar pairing of dark annuli, caused not by altered annular spacing but by deposition of distinct summer accessory lines. Paired dark annuli in females accurately reflected known cub-rearing records, although it was more difficult to determine the years of cub production (reading teeth from the outer annulus inward) than the ages of females when they produced cubs (counting annuli outward from the dentin–cementum interface). The distribution of ages of first reproduction gleaned from teeth of harvested females coincided with that of females with known reproductive histories, indicating that teeth currently collected from harvested black bears by management agencies across North America could provide reasonably good accounts of both present and past reproductive rates.