Unmanned aerial vehicles (UAVs) have the potential to revolutionize the way research is conducted in many scientific fields 1, 2. UAVs can access remote or difficult terrain 3, collect large amounts ...of data for lower cost than traditional aerial methods, and facilitate observations of species that are wary of human presence 4. Currently, despite large regulatory hurdles 5, UAVs are being deployed by researchers and conservationists to monitor threats to biodiversity 6, collect frequent aerial imagery 7–9, estimate population abundance 4, 10, and deter poaching 11. Studies have examined the behavioral responses of wildlife to aircraft 12–20 (including UAVs 21), 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 22, and when linked to locational information, it can be used to determine events 19, 23, 24 or components of an animal’s environment 25 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.
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•Cardiac biologgers reveal that bears exhibit a stress response to UAV flights•Bears rarely display a behavioral response, measured by GPS collars, to UAV flights•Magnitudes of heart rate spikes were correlated with wind speed and proximity of UAV
Unmanned aerial vehicles (UAVs; i.e., “drones”) are increasingly popular tools for ecological research. Ditmer et al. used GPS collars and cardiac biologgers to assess effects of UAV flights on free-roaming bears. All bears exhibited a stress response to UAV flights as evidenced by elevated heart rates while rarely exhibiting a behavioral response.
Among the world's large Carnivores, American black bears (Ursus americanus) are the foremost conservation success story. Populations have been expanding across North America because the species is ...adaptable and tolerant of living near people, and because management agencies in the U.S. and Canada controlled hunting and other human-sources of mortality. As a result, human-black bear conflicts (damage to property, general nuisance, threat to human safety) have dramatically increased in some areas, making it urgently important to develop and deploy a variety of mitigation tools. Previous studies claimed that legal hunting did not directly reduce conflicts, but they did not evaluate whether hunting controlled conflicts via management of population size. Here, we compared temporal patterns of phoned-in complaints about black bears (total ~63,500) in Minnesota, USA, over 4 decades to corresponding bear population estimates: both doubled during the first decade. We also quantified natural bear foods, and found that large year-to-year fluctuations affected numbers of complaints; however, since this variation is due largely to weather, this factor cannot be managed. Complaints fell sharply when the management agency (1) shifted more responsibility for preventing and mitigating conflicts to the public; and (2) increased hunting pressure to reduce the bear population. This population reduction was more extreme than intended, however, and after hunting pressure was curtailed, population regrowth was slower than anticipated; consequently both population size and complaints remained at relatively low levels statewide for 2 decades (although with local hotspots). These long-term data indicated that conflicts can be kept in tolerable bounds by managing population size through hunting; but due to the bluntness of this instrument and deficiencies and uncertainties in monitoring and manipulating populations, it is wiser to maintain a population at a level where conflicts are socially-acceptable than try to reduce it once it is well beyond that point.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Human‐bear conflicts cause annoyance, financial losses, injuries, and even death to people. In poorer parts of the world, conflicts with bears can affect local economies. Retaliation against bears ...may threaten the future of small, isolated populations. Our survey of the world's bear experts revealed that the problem is worsening in terms of severity of conflicts and their impact on bear conservation on all four continents inhabited by bears. However, the main drivers of conflict, and its manifestations, differ among bear species. We reviewed human‐bear conflict management plans from which we identified 10 categories of mitigating interventions that together comprise a ubiquitous bear conflict management toolbox. Within this toolbox, the peer‐reviewed literature indicates heavy reliance on education and physical barriers for conflict mitigation. In customizing these general approaches to local circumstances, it is important to be mindful of starkly varying geopolitical and social circumstances. There is a pressing need to improve transfer of knowledge from places with active empirical research on mitigation (especially North America), and adapting methodologies to other parts of the world. We saw little evidence of evaluation and adaptive management in the conflict plans. Failure to mitigate conflicts may reduce society's tolerance of bears and diminish conservation efforts.
Sloth bears are non‐carnivorous yet they attack more people than any other bear. They often stand up and charge explosively if a person mistakenly gets too close. Here, we argue that their aggression ...toward humans is an extension of their behavior toward tigers, which are their only natural predator. Interactions between sloth bears and tigers have not previously been studied because scientists have rarely observed such events. We collected and examined 43 videos or photo documentations of sloth bear–tiger interactions posted on the internet or social media from 2011 to 2023, mainly by tourists visiting tiger parks in India. We observed that sloth bears were most likely to stand up and charge if they first became aware of the tiger at close range (<3 m away). This aggressive–defensive strategy, intended to dissuade the tiger from attacking, appeared to be successful, in that 86% of interactions ended with no contact, whereas four (9%) culminated in the bear's death. We propose that a myrmecophagous diet led to this species' aggressive behavior: (1) their long, blunt front claws, well adapted for digging termites and ants, hamper their ability to climb trees for escape, and (2) they walk with their head down focused on scents underground, and make considerable noise digging and blowing soil, enabling tigers to approach quite closely without being detected. Sloth bears have coexisted with tigers or other (now extinct) large felid predators for their entire evolutionary history. Whereas their aggressive behavior has served them well for millions of years, more recently, people's fear of and retaliation against sloth bears represents a major threat to their survival. Understanding how sloth bears react to tigers provides guidance for reducing attacks on humans, thereby contributing to sloth bear conservation. Our investigation was made possible by passive citizen scientists, who unknowingly collected valuable data.
We collected and examined 43 videos, and photo documentations, of sloth bear–tiger interactions posted on the internet or social media mainly by tourists visiting tiger parks in India. We observed that sloth bears were most likely to stand up and charge if they first became aware of the tiger at close range (<3 m away). This aggressive–defensive strategy, intended to dissuade the nearby tiger from attacking, appeared to be successful, in that 86% of interactions ended with no contact, whereas four (9%) culminated in the bear's death. The photographer of the photo in the graphical is Vikram Hiresavi.
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
(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.
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.
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.
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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
American black bears frequently abandon their home ranges in late summer and move to feeding areas to fatten themselves for hibernation. We examined seasonal movements of 206 radio-collared bears in ...north-central Minnesota during 1981-1990. We exploited the variability in this long-term data set to test tradeoffs for animals leaving their home range. Late summer movements were common for both sexes and all ages (39% of females, 44% of males), but were variable from year-to-year in prevalence, timing, and destination. Bears typically left their summer home ranges in August and returned ~6 weeks later in September or October. Most traveled southward, where acorns were more plentiful (median = 10 km for females, 26 km for males; maximum = 168 km). These facultative migrations were most common when rich resources were available outside home ranges. Bears were least apt to leave when foods were scarce in their home range, possibly sensing a risk of migrating during a widespread food failure. Among females, those whose body mass was close to a reproductive threshold were most prone to migrate. Migrating bears were less likely to be killed by hunters, suggesting that they were especially vigilant.
At the most basic level, the assessment of a species’ status involves knowing where it occurs. Determining the presence of rare species is difficult, and can be further confounded by the presence of ...a more common look-alike species. We investigated one of the few places in the world where three species of bears have been reported to co-occur at a fine scale: Balpakram National Park, Meghalaya, India. Asiatic black bears (Ursus thibetanus) are fairly common, and we sought to determine whether sun bears (Helarctos malayanus) and/or sloth bears (Melursus ursinus) also resided there. The local Garo language has words for three types of bears, and some local people reported the continued presence of a small type of bear, possibly the sun bear, but the probable extirpation of sloth bears. Because these bears look somewhat alike, local people and government forest officers could not provide convincing accounts of the presence of more than one species. We measured claw marks on climbed trees, a method used to differentiate sun bears from Asiatic black bears where both are known to occur; however, this method turned out to be unreliable for detecting sun bears where their presence was unknown because sun bear-sized marks are not distinguishable from juvenile black bears. We recommend targeted camera trapping near recent purported sightings of the other two bear species.
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 (δ13C and δ15N) 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.
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