The contamination status on persistent organic pollutants (POPs) in the Croatian terrestrial ecosystem was investigated by analyzing two classes of contaminants in adipose tissue of male European brown bear (Ursus arctos, N = 27) collected in 2021 and 2022. In addition to seven indicator polychlorinated biphenyls (PCBs), for the first time seven polybrominated diphenyl ethers (PBDEs) were analyzed in terrestrial species from this region. Sum of mass fractions detected in adipose tissue ranged from 0.011 to 0.463 ng g-1 lipid weight (lw) for the PBDEs, and from 0.652 to 30.17 ng g-1 lw for PCBs, with two orders of magnitude difference in the median value for these two groups of POPs (PBDEs: 0.022 ng g-1 lw; PCBs: 2.307 ng g-1 lw). PCBs dominated over PBDEs with a share of over 94 % of the total mass fractions of both groups of analyzed POPs. Results of the comparison of the PCB levels in the adipose tissue of brown bears reported here and in previous investigation from this region showed decrease in PCB-28, but increase of PCB-118 and PCB-180, while other congeners seemed to have reached a steady-state level in the environment over a ten-year period. Among the compounds analyzed in this study, BDE-47, PCB-153 and PCB-180 were the dominant congeners. Somewhat higher sum of PCBs was measured in April compared to October, although not statistically significant, indicating possible impact of winter hibernation causing concentration of lipophilic compounds due to body fat loss. Revealed POP levels in brown bears are consistent with the data on the low contamination of the Croatian terrestrial ecosystem in general.

Harvest regulations commonly attenuate the consequences of hunting on specific segments of a population. However, regulations may not protect individuals from non-lethal effects of hunting and their consequences remain poorly understood. In this study, we compared the movement rates of Scandinavian brown bears (Ursus arctos, n = 47) across spatiotemporal variations in risk in relation to the onset of bear hunting. We tested two alternative hypotheses based on whether behavioural responses to hunting involve hiding or escaping. If bears try to reduce risk exposure by avoiding being detected by hunters, we expect individuals from all demographic groups to reduce their movement rate during the hunting season. On the other hand, if bears avoid hunters by escaping, we expect them to increase their movement rate in order to leave high-risk areas faster. We found an increased movement rate in females accompanied by dependent offspring during the morning hours of the bear hunting season, a general decrease in movement rate in adult lone females, and no changes in males and subadult females. The increased movement rate that we observed in females with dependant offspring during the hunting season was likely an antipredator response because it only occurred in areas located closer to roads, whereas the decreased movement rate in lone females could be either part of seasonal activity patterns or be associated with an increased selection for better concealment. Our study suggests that female brown bears accompanied by offspring likely move faster in high-risk areas to minimize risk exposure as well as the costly trade-offs (i.e. time spent foraging vs. time spent hiding) typically associated with anti-predator tactics that involve changes in resource selection. Our study also highlights the importance of modelling fine-scale spatiotemporal variations in risk to adequately capture the complexity in behavioural responses caused by human activities in wildlife.

Hibernation is a period of metabolic suppression utilized by many small and large mammal species to survive during winter periods. As the underlying cellular and molecular mechanisms remain incompletely understood, our study aimed to determine whether skeletal muscle myosin and its metabolic efficiency undergo alterations during hibernation to optimize energy utilization. We isolated muscle fibers from small hibernators, Ictidomys tridecemlineatus and Eliomys quercinus and larger hibernators, Ursus arctos and Ursus americanus. We then conducted loaded Mant-ATP chase experiments alongside X-ray diffraction to measure resting myosin dynamics and its ATP demand. In parallel, we performed multiple proteomics analyses. Our results showed a preservation of myosin structure in U. arctos and U. americanus during hibernation, whilst in I. tridecemlineatus and E. quercinus, changes in myosin metabolic states during torpor unexpectedly led to higher levels in energy expenditure of type II, fast-twitch muscle fibers at ambient lab temperatures (20 °C). Upon repeating loaded Mant-ATP chase experiments at 8 °C (near the body temperature of torpid animals), we found that myosin ATP consumption in type II muscle fibers was reduced by 77-107% during torpor compared to active periods. Additionally, we observed Myh2 hyper-phosphorylation during torpor in I. tridecemilineatus, which was predicted to stabilize the myosin molecule. This may act as a potential molecular mechanism mitigating myosin-associated increases in skeletal muscle energy expenditure during periods of torpor in response to cold exposure. Altogether, we demonstrate that resting myosin is altered in hibernating mammals, contributing to significant changes to the ATP consumption of skeletal muscle. Additionally, we observe that it is further altered in response to cold exposure and highlight myosin as a potentially contributor to skeletal muscle non-shivering thermogenesis.
Many animals use hibernation as a tactic to survive harsh winters. During this dormant, inactive state, animals reduce or limit body processes, such as heart rate and body temperature, to minimise their energy use. To conserve energy during hibernation, animals can use different approaches. For example, garden dormice undergo periodic states of extremely low core temperatures (down to 4–8oC); whereas Eurasian brown bears see milder temperature drops (down to 23–25oC). An important organ that changes during hibernation is skeletal muscle. Skeletal muscle typically uses large amounts of energy, making up around 50% of body mass. To survive, hibernating animals must change how their skeletal muscle uses energy. Traditionally, active myosin – a protein found in muscles that helps muscles to contract – was thought to be responsible for most of the energy use by skeletal muscle. But, more recently, resting myosin has also been found to use energy when muscles are relaxed. Lewis et al. studied myosin and skeletal muscle energy use changes during hibernation and whether they could impact the metabolism of hibernating animals. Lewis et al. assessed myosin changes in muscle samples from squirrels, dormice and bears during hibernation and during activity. Experiments showed changes in resting myosin in squirrels and dormice (whose temperature drops to 4–8oC during hibernation) but not in bears. Further analysis revealed that cooling samples from non-hibernating muscle to 4–8oC increased energy use in resting myosin, thereby generating heat. However, no increase in energy use was found after cooling hibernating muscle samples to 4–8oC. This suggest that resting myosin generates heat at cool temperatures – a mechanism that is switched off in hibernating animals to allow them to cool their body temperature. These findings reveal key insights into how animals conserve energy during hibernation. In addition, the results show that myosin regulates energy use in skeletal muscles, which indicates myosin may be a potential drug target in metabolic diseases, such as obesity.

Large carnivores have recently increased in number and recolonized in human-dominated landscapes; however, their ecological roles in these landscapes have not been well studied. In the Shiretoko World Heritage (SWH) site, brown bears have recolonized a previously abandoned mosaic landscape of natural forests and conifer plantations after land abandonment. We previously reported that the bears had recently begun to dig for cicada nymphs in association with the creation of larch plantations. As a result, this digging activity decreased soil nutrients. To deepen the understanding of the novel ecological role of brown bears within human-modified landscapes, we examined the impacts of brown bear digging on the growth of larch trees. We found that brown bear digging decreased fine root biomass of larch, soil water, and nitrogen availability. Brown bear digging negatively affected needle nitrogen content, but not carbon isotope ratios, a water stress index of trees. Tree ring data suggest that digging negatively affected the radial growth of larches. The results imply that digging decreases tree growth due to limited soil nitrogen uptake. Our findings indicate that the ecological roles of large carnivores may differ between natural and anthropogenic landscapes.

Understanding mortality causes is important for the conservation of endangered species, especially in small and isolated populations inhabiting anthropized landscapes where both natural and human-caused mortality may hinder the conservation of these species. We investigated the mortality causes of 53 free-ranging brown bears (Ursus arctos) found dead between 1998 and 2023 in the Cantabrian Mountains (northwestern Spain), a highly human-modified region where bears are currently recovering after being critically threatened in the last century. We detected natural traumatic injuries in 52.63% and infectious diseases in 39.47% of the 38 bears for which the mortality causes were registered, with 21.05% of these cases presenting signs of both infectious diseases and traumas. More specifically, almost 30% of the bears died during or after intraspecific fights, including sexually selected infanticide (10.53%). In addition, primary infectious diseases such as infectious canine hepatitis, distemper, clostridiosis and colibacillosis caused the death of 15.79% of the bears. The number of direct human-caused deaths (i.e., shooting, poisoning, snare) decreased over the study period. This study also reveals three new mortality causes triggered by pathogens, two of which-Clostridium novyi and verotoxigenic Escherichia coli-not previously described in ursids, and the other one, canine distemper virus, never reported in brown bears as cause of death. New management strategies for the conservation of Cantabrian bears, which are urgently needed due to the rapid expansion of the population, should consider the mortality causes described in this study and must promote further research to elucidate how the high prevalence of infectious diseases may threaten the current recovery of the population.

This study aimed to investigate the variations of parasites in the feces of brown bears Ursus arctos inhabiting the Cantabrian Mountains (NW Spain). A total of 248 bear fecal samples were collected throughout one year, spanning from August 2018 to September 2019, at an approximate frequency of 20 samples per month. The results were analyzed in relation to both the season and the biological activity of the brown bears, i.e., hibernation, mating and hyperphagia. Among the examined samples, eggs of Dicrocoelium dendriticum (32.2%; 95% Confidence Interval: 26.4-38.1), Baylisascaris sp. (44.8%; 38.5-50.9), ancylostomatids (probably belonging to Uncinaria spp.) (16.5%; 11.9-21.1) and Trichuris sp. (1.2%; 0-2.6) were observed. Significant seasonal differences were noted for Baylisascaris and ancylostomatids (χ2 = 21.02, P = 0.001 and χ2 = 34.41, P = 0.001, respectively). Furthermore, the presence of helminth eggs was correlated with the activity phase of the brown bears. Dicrocoelium attained the highest prevalence during the mating phase, while Baylisascaris and ancylostomatids were more frequent during hyperphagia. Notably, the highest egg-output counts for Dicrocoelium and Baylisascaris sp. were recorded during the mating phase and hibernation, respectively, whereas ancylostomatids eggs peaked during hyperphagia. Additionally, variations in egg-output counts were significant for all helminths concerning the season, with the exception of Trichuris sp., and for Dicrocoelium and Baylisascaris sp. According to bear activity. It is concluded that infection by gastrointestinal helminths depends on the season and the biological activity of the bears from the Cantabrian Mountains, and their health status could result influenced.

Although the advent of high-resolution GPS tracking technology has helped increase our understanding of individual and multispecies behavior in wildlife systems, detecting and recording direct interactions between free-ranging animals remains difficult. In 2023, we deployed GPS collars equipped with proximity sensors (GPS proximity collars) on brown bears (Ursus arctos) and moose (Alces alces) as part of a multispecies interaction study in central Sweden. On 6 June, 2023, a collar on an adult female moose and a collar on an adult male bear triggered each other\'s UHF signal and started collecting fine-scale GPS positioning data. The moose collar collected positions every 2 min for 89 min, and the bear collar collected positions every 1 min for 41 min. On 8 June, field personnel visited the site and found a female neonate moose carcass with clear indications of bear bite marks on the head and neck. During the predation event, the bear remained at the carcass while the moose moved back and forth, moving toward the carcass site about five times. The moose was observed via drone with two calves on 24 May and with only one remaining calf on 9 June. This case study describes, to the best of our knowledge, the first instance of a predation event between two free ranging, wild species recorded by GPS proximity collars. Both collars successfully triggered and switched to finer-scaled GPS fix rates when the individuals were in close proximity, producing detailed movement data for both predator and prey during and after a predation event. We suggest that, combined with standard field methodology, GPS proximity collars placed on free-ranging animals offer the ability for researchers to observe direct interactions between multiple individuals and species in the wild without the need for direct visual observation.

How organisms obtain energy to survive and reproduce is fundamental to ecology, yet researchers use theoretical concepts represented by simplified models to estimate diet and predict community interactions. Such simplistic models can sometimes limit our understanding of ecological principles. We used a polyphagous species with a wide distribution, the brown bear (Ursus arctos), to illustrate how disparate theoretical frameworks in ecology can affect conclusions regarding ecological communities. We used stable isotope measurements (δ13 C, δ15 N) from hairs of individually monitored bears in Sweden and Bayesian mixing models to estimate dietary proportions of ants, moose, and three berry species to compare with other brown bear populations. We also developed three hypotheses based on predominant foraging literature, and then compared predicted diets to field estimates. Our three models assumed (1) bears forage to optimize caloric efficiency (optimum foraging model), predicting bears predominately eat berries (~70% of diet) and opportunistically feed on moose (Alces alces) and ants (Formica spp. and Camponotus spp; ~15% each); (2) bears maximize meat intake (maximizing fitness model), predicting a diet of 35%-50% moose, followed by ants (~30%), and berries (~15%); (3) bears forage to optimize macronutrient balance (macronutrient model), predicting a diet of ~22% (dry weight) or 17% metabolizable energy from proteins, with the rest made up of carbohydrates and lipids (~49% and 29% dry matter or 53% and 30% metabolizable energy, respectively). Bears primarily consumed bilberries (Vaccinium myrtillus; 50%-55%), followed by lingonberries (V. vitis-idaea; 22%-30%), crowberries (Empetrum nigrum; 8%-15%), ants (5%-8%), and moose (3%-4%). Dry matter dietary protein was lower than predicted by the maximizing fitness model and the macronutrient balancing model, but protein made up a larger proportion of the metabolizable energy than predicted. While diets most closely resembled predictions from optimal foraging theory, none of the foraging hypotheses fully described the relationship between foraging and ecological niches in brown bears. Acknowledging and broadening models based on foraging theories is more likely to foster novel discoveries and insights into the role of polyphagous species in ecosystems and we encourage this approach.

A morphological description is provided for a unique find of a frozen mummified subfossil brown bear (Ursus arctos L., 1758), found for the first time ever. The find is a well-preserved bear carcass of approximately 3500 years in age. Results of computed tomography and DNA testing are discussed.

In Japan, the recent series of sporadic outbreaks of human trichinellosis caused by Trichinella (Nematoda: Trichocephalida) has occurred owing to the consumption of raw or insufficiently cooked meat from wild bears. However, the infection status and molecular characteristics of Trichinella larvae in Japanese wild bears remain poorly understood. This study investigated the prevalence of Trichinella spp. in brown bears (Ursus arctos) from Hokkaido, and Japanese black bears (Ursus thibetanus japonicus) from three prefectures (Aomori, Akita, and Iwate) in northern Japan, between April 2019 and August 2022. Trichinella larvae were detected in 2.5% (6/236) of the brown bears and 0.9% (1/117) of the Japanese black bears. Sequence analysis using two genetic loci, the internal transcribed spacer region of nuclear ribosomal DNA and the mitochondrial cytochrome c oxidase subunit I gene, revealed that the larvae collected from the seven infected bears were identical to one of the two haplotypes of Trichinella T9. The prevalence of Trichinella T9 is low but is maintained in bears in the Hokkaido and Iwate prefectures suggesting that undercooked meat from these animals could cause human infection. Thus, continued health education campaigns are needed to raise awareness of the potential risk of trichinellosis among hunters, meat suppliers, consumers, and local governmental health agencies.