Janene Auger

Grizzly bears (Ursus arctos horribilis) and black bears (Ursus americanus) prevent trabecular bone loss during disuse (hibernation)

Disuse typically causes an imbalance in bone formation and bone resorption, leading to losses of cortical and trabecular bone. In contrast, bears maintain balanced intracortical remodeling and prevent cortical bone loss during disuse (hibernation). Trabecular bone, however, is more detrimentally affected than cortical bone in other animal models of disuse. Here we investigated the effects of hibernation on bone remodeling, architectural properties, and mineral density of grizzly bear (Ursus arctos horribilis) and black bear (Ursus americanus) trabecular bone in several skeletal locations. There were no differences in bone volume fraction or tissue mineral density between hibernating and active bears or between pre- and post-hibernation bears in the ilium, distal femur, or calcaneus. Though indices of cellular activity level (mineral apposition rate, osteoid thickness) decreased, trabecular bone resorption and formation indices remained balanced in hibernating grizzly bears. These data suggest that bears prevent bone loss during disuse by maintaining a balance between bone formation and bone resorption, which consequently preserves bone structure and strength. Further investigation of bone metabolism in hibernating bears may lead to the translation of mechanisms preventing disuse-induced bone loss in bears into novel treatments for osteoporosis.

Six months of disuse during hibernation does not increase intracortical porosity or decrease cortical bone geometry, strength, or mineralization in black bear (Ursus americanus) femurs.

Disuse typically uncouples bone formation from resorption, leading to bone loss which compromises bone mechanical properties and increases the risk of bone fracture. Previous studies suggest that bears can prevent bone loss during long periods of disuse (hibernation), but small sample sizes have limited the conclusions that can be drawn regarding the effects of hibernation on bone structure and strength in bears. Here we quantified the effects of hibernation on structural, mineral, and mechanical properties of black bear (Ursus americanus) cortical bone by studying femurs from large groups of male and female bears (with wide age ranges) killed during pre-hibernation (fall) and post-hibernation (spring) periods. Bone properties that are affected by body mass (e.g. bone geometrical properties) tended to be larger in male compared to female bears. There were no differences (p>0.226) in bone structure, mineral content, or mechanical properties between fall and spring bears. Bone geometrical properties differed by less than 5% and bone mechanical properties differed by less than 10% between fall and spring bears. Porosity (fall: 5.5+/-2.2%; spring: 4.8+/-1.6%) and ash fraction (fall: 0.694+/-0.011; spring: 0.696+/-0.010) also showed no change (p>0.304) between seasons. Statistical power was high (>72%) for these analyses. Furthermore, bone geometrical properties and ash fraction (a measure of mineral content) increased with age and porosity decreased with age. These results support the idea that bears possess a biological mechanism to prevent disuse and age-related osteoporoses.

Are American Black Bears (Ursus Americanus) Legitimate Seed Dispersers for Fleshy-Fruited Shrubs?

Abstract Seeds of seven fleshy-fruited shrubs used by American black bears (Ursus americanus) were extracted from fresh fruit (controls) and from scats of free-ranging and captive bears (ingestion treatments). Effects of the digestive process on viability, germinability and germination rate were measured against controls. Results were species specific. Filled control seeds of all species were highly viable (>74%). Digestion by bears had no significant effect on initial viability, except for serviceberry (Amelanchier alnifolia) for which viability of seeds passed through captive bears decreased 14%. Percent germination of control seeds summed over five chilling durations at 1 C was significantly different from that of at least one bear ingestion treatment for five of the seven species. For chokecherry (Prunus virginiana), Oregon grape (Mahonia repens) and skunkbush sumac (Rhus trilobata), seeds ingested by wild black bears germinated to a significantly higher percentage than controls, but for snowberry (Symphoricarpos oreophilus) control seeds germinated significantly better. For serviceberry all viable seeds germinated after sufficient chilling, but germination of controls was higher than ingested seeds after shorter chilling durations. When seeds were prewarmed for 5 wk before chilling, percent germination of Oregon grape, skunkbush sumac and snowberry significantly increased. For serviceberry, prewarming lengthened the minimum chilling requirement from 7 to 14 wk. Results from ingestion treatments suggest that the digestive process of black bears may simulate prewarming of seeds. Future work clarifying the role of bears as seed dispersers should involve characterization of: (1) scat deposition sites, (2) activities of seed predators and secondary dispersers at the scats and (3) the relative importance of bears in communities containing other dispersal agents.

Yellow-bellied marmots (Marmota flaviventris) preserve bone strength and microstructure during hibernation.

Reduced skeletal loading typically results in decreased bone strength and increased fracture risk for humans and many other animals. Previous studies have shown bears are able to prevent bone loss during the disuse that occurs during hibernation. Studies with smaller hibernators, which arouse intermittently during hibernation, show that they may lose bone at the microstructural level. These small hibernators, like bats and squirrels, do not utilize intracortical remodeling. However, slightly larger mammals like marmots do. In this study we examined the effects of hibernation on bone structural, mineral, and mechanical properties in yellow-bellied marmots (Marmota flaviventris). This was done by comparing cortical bone properties in femurs and trabecular bone properties in tibias from marmots killed before hibernation (fall) and after hibernation (spring). Age data were not available for this study; however, based on femur length the post-hibernation marmots were larger than the pre-hibernation marmots. Thus, cross-sectional properties were normalized by allometric functions of bone length for comparisons between pre- and post-hibernation. Cortical thickness and normalized cortical area were higher in post-hibernation samples; no other normalized cross-sectional properties were different. No cortical bone microstructural loss was evident in osteocyte lacunar measurements, intracortical porosity, or intracortical remodeling cavity density. Osteocyte lacunar area, porosity, and density were surprisingly lower in post-hibernation samples. Trabecular bone volume fraction was not different between pre- and post-hibernation. Measures of both trabecular and cortical bone mineral content were higher in post-hibernation samples. Three-point bending failure load, failure energy, elastic energy, ultimate stress, and yield stress were all higher in post-hibernation samples. These results support the idea that, like bears, marmots are able to prevent disuse osteoporosis during hibernation, thus preventing increased fracture risk and promoting survival of the extreme environmental conditions that occur in hibernation.

Black bear femoral geometry and cortical porosity are not adversely affected by ageing despite annual periods of disuse (hibernation)

Disuse (i.e. inactivity) causes bone loss, and a recovery period that is 2–3 times longer than the inactive period is usually required to recover lost bone. However, black bears experience annual disuse (hibernation) and remobilization periods that are approximately equal in length, yet bears maintain or increase cortical bone material properties and whole bone mechanical properties with age. In this study, we investigated the architectural properties of bear femurs to determine whether cortical structure is preserved with age in bears. We showed that cross‐sectional geometric properties increase with age, but porosity and resorption cavity density do not change with age in skeletally immature male and female bears. These findings suggest that structural properties substantially contribute to increasing whole bone strength with age in bears, particularly during skeletal maturation. Porosity was not different between skeletally immature and mature bears, and showed minimal regional variations between anatomical quadrants and radial positions that were similar in pattern and magnitude between skeletally immature and mature bears. We also found gender dimorphisms in bear cortical bone properties: females have smaller, less porous bones than males. Our results provide further support for the idea that black bears possess a biological mechanism to prevent disuse osteoporosis.

Grizzly Bears (Ursus Arctos Horribilis) and Black Bears (Ursus Americanus) Prevent Trabecular Bone Loss During Disuse (Hibernation)

Reduced skeletal loading causes cortical and trabecular bone loss in humans and other animals, but trabecular bone responds to disuse more rapidly and shows greater losses than cortical bone for a given period of inactivity [1–2]. Manifestations of disuse on trabecular bone include unbalanced bone remodeling, decreased bone mineral density, and compromised bone architecture [3].Copyright

The late-denning activities of the American black bear in Utah

Abstract Understanding the timing of den emergence and departure allows management agencies to establish hunting seasons that minimize the take of females with dependent young, protects denned bears from human disturbances, and extends our understanding of the ecology of these mammals. We determined the mean den emergence date ( = 25 Mar), the number of days at the den site post-emergence ( = 11 days), and the mean den departure date ( = 8 Apr) for female American black bears in Utah, USA, from 2011 to 2013. We analyzed the effects of bear cohort, region of Utah, year, elevation, and weather on emergence, departure, and total number of days at den site post-emergence using model selection and model-averaging. First emergence date (n = 37) differed among cohorts and was negatively correlated with spring temperature. Den departure date (n = 21) differed among ecoregions and was negatively correlated with spring temperature during emergence and temperature the spring and summer before denning. Total number of days at den (n = 21) differed among cohorts and was negatively correlated with last frost date in spring from year before. We also described behaviors observed at the den site. Bears spent little of the late-denning period outside of the den ( = 9.8% of total observation time). When outside the den, bears spent the majority of the time walking, standing, sitting, and lying down. We also observed several unique behaviors including gathering nest materials, nursing, ingesting, and visitation of den sites by other wildlife.