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At least 73 records · Page 4Linked to original sources

USGS2018

Exposure of Alaska brown bears (Ursus arctos) to bacterial, viral, and parasitic agents varies spatiotemporally and may be influenced by age

We collected blood and serum from 155 brown bears ( Ursus arctos ) inhabiting five locations in Alaska during 2013–16 and tested samples for evidence of prior exposure to a suite of bacterial, viral, and parasitic agents. Antibody seroprevalence among Alaska brown bears was estimated to be 15% for Brucella spp., 10% for Francisella tularensis , 7% for Leptospira spp., 18% for canine adenovirus type 1 (CAV-1), 5% for canine distemper virus (CDV), 5% for canine parvovirus, 5% for influenza A virus (IAV), and 44% for Toxoplasma gondii . No samples were seropositive for antibodies to Trichinella spp. Point estimates of prior exposure to pathogens among brown bears at previously unsampled locations generally fell within the range of estimates for previously or contemporaneously sampled bears in Alaska. Statistical support was found for variation in antibody seroprevalence among bears by location or age cohort for CAV-1, CDV, IAV, and Toxoplasma gondii . There was limited concordance in comparisons between our results and previous serosurveys regarding spatial and age-related trends in antibody seroprevalence among Alaska brown bears suggestive of temporal variation. However, we found evidence that the seroprevalence of CAV-1 antibodies is consistently high in bears inhabiting SW Alaska and the cumulative probability of exposure may increase with age. We found evidence for seroconversion or seroreversion to six different infectious agents in one or more bears. Results of this study increase our collective understanding of disease risk to both Alaska brown bear populations and humans that utilize this resource.

Alaska↗

USGS2025

Hemoglobin A1c is a retrospective indicator of denning in polar bears (Ursus maritimus)

The nutritional health of polar bears ( Ursus maritimus) is tied to reproductive success, and fasting status can be used to infer recent reproductive history. However, the methods currently used to determine denning and fasting status have their limitations. We examined hemoglobin A1c (HbA1c), an integrative metric of average blood glucose levels over recent months, in free-ranging Southern Beaufort Sea polar bears to assess its usefulness in determining reproductive status and fasting. We compared HbA1c between bears recently in maternity dens that included spring-captured females that were accompanied by cubs-of-the-year ( n = 38), and non-denned bears that included spring-captured females that were accompanied by 1- or 2-yr-old cubs ( n = 39). We predicted that HbA1c would be higher in denned females compared to non-denned females, due to the combined effects of increased circulating glucose associated with insulin resistance from fasting and gestation, as well as the energy mobilization required during early lactation. HbA1c was measured in Polar Bear whole blood samples using an enzymatic assay for quantifying HbA1c and expressed as the percentage of glycated hemoglobin over total hemoglobin. Denned females had higher mean HbA1c ( x̅ 4.70%, 95% CI = 4.54%, 4.86%) than non-denned ( ⁠ x̅ 4.38%, 95% CI = 4.23%, 4.53%, P = 0.005). We trained a binary logistic regression model to classify the probability of recent prior denning based on HbA1c and glucose, and the model classified denning with 75% accuracy. HbA1c can be used as an effective tool for determining denning history and could have implications for monitoring reproductive success.

Alsaka, Northwest Territories, Yukon↗

USGS1993

Cub adoption by brown bears (Ursus arctos middendorffi) on Kodiak Island, Alaska

We report three cases where female Brown Bears (Ursus arctos middendorffi) with new (1 winter season. The adoptions occurred in a sampling of 104 litters produced by 89 different females on Kodiak Island, Alaska during 1982-1990. A maximum of six cubs were reared from litters that probably would have produced 3-4 subadults if the adoptions had not taken place.

Canadian Field-Naturalist↗

USGS2001

Black bear (Ursus americanus Pallas) feeding damage across timber harvest edges in northern California coast redwood (Sequoia sempervirens[D. Don] Endl.) forests, USA

Feeding damage to trees by black bears (Ursus americanus Pallas) was recorded in proximity to timber harvest edges in harvested and old-growth stands of coast redwood (Sequoia sempervirens [D. Don] Endl.) in northern California, USA. Bears exhibited distinct preference in their feeding patterns related to stand structure and composition and to distance from the timber-harvest edge. Most damage was recorded within regenerating stands. Regression analysis indicated that density of damaged trees was negatively correlated with distance from timber harvest edges within old-growth stands. A significant negative correlation was also found between the density of trees damaged by bears and habitat diversity (H') as measured by the Shannon diversity index. In addition, bears exhibited preference for pole-size trees (dbh = 10-50 cm) over all other size classes, and coast redwood over other species. In general, damage by bears appeared to act as a natural thinning agent in even-aged stands. No damage was recorded in old-growth stands except in close proximity to the timber-harvest edge where subcanopy recruitment was high.

California↗

USGS1997

Population genetic studies of the polar bear ( Ursus maritimus ): A summary of available data and interpretation of results

A summary of existing population genetics literature is presented for polar bears ( Ursus maritimus ) and interpreted in the context of the species' life-history characteristics and regional heterogeneity in environmental regimes and movement patterns. Several nongenetic data sets including morphology, contaminant levels, geographic variation in reproductive characteristics, and the location and distribution of open-water foraging habitat suggest some degree of spatial structuring. Eleven populations are recognized by the IUCN Polar Bear Specialist Group. Few genetics studies exist for polar bears. Interpretation and generalizations of regional variation in intra- and interpopulation levels of genetic variability are confounded by the paucity of data from many regions and by the fact that no single informative genetic marker has been employed in multiple regions. Early allozyme studies revealed comparatively low levels of genetic variability and no compelling evidence of spatial structuring. Studies employing mitochondrial DNA (mtDNA) also found low levels of genetic variation, a lack of phylogenetic structure, and no significant evidence for spatial variation in haplotype frequency. In contrast, microsatellite variable number of tandem repeat (VNTR) loci have revealed significant heterogeneity in allele frequency among populations in the Canadian Arctic. These regions are characterized by archipelgic patterns of sea-ice movements. Further studies using highly polymorphic loci are needed in regions characterized by greater polar bear dependency on pelagic sea-ice movements and in regions for which no data currently exist (i.e., Laptev and Novaya Zemlya/Franz Josef).

Book chapter↗

USGS2021

American Black Bear (Ursus americanus)

American black bears (Ursus americanus) are endemic to North America, having speciated from other ursids some 1.2 to 1.8 million years ago (Kurtn & Anderson 1994). During that time, black bears came to occupy nearly all of the forested areas of the North American continent. Historically, black bears were one of the most important mammals to indigenous peoples of North America by providing food, fat, hides, and tools (Raybourne 1987). Bears also played important roles in indigenous culture as symbols of strength, hard work, and love (see Rockwell 1991). In the 18th and 19th centuries in the U.S., Canada, and Mexico, European settlers with firearms reduced black bear numbers (Williams 1930), but the axe and plow had equally negative effects on bear populations as forests gave way to agriculture and livestock. Black bears also faced intense pressure from unregulated market hunting, poaching, and predator control programs. Black bears disappeared from large portions of their North American range, being relegated to swamps, thickets, rugged mountains, and other areas deemed too inaccessible, unsuitable, or undesirable to be occupied by humans (Pelton & van Manen 1994). In the early 20th century, Canadian and U.S. governments established national parks, forests, and refuges, and state and provincial legislatures created wildlife management agencies and enacted regulations to manage wildlife populations. By the late 20th century, the combination of public land infrastructure, habitat improvements, harvest regulations, law enforcement, and information-education programs resulted in significant increases in black bear numbers and range expansions in the U.S. and Canada (Pelton & van Manen 1994), aided in no small part by the remarkable adaptability of this animal (Pelton 2003; Scheick & McCown 2014). Today, the American black bear is one of the most iconic, abundant, and economically important bear species in the world. Unfortunately, black bear populations in Mexico have not recovered similarly to those in the U.S and Canada, and the status of the species there is uncertain.

Book chapter↗

USGS2015

Gene transcription in polar bears ( Ursus maritimus ) from disparate populations

Polar bears in the Beaufort (SB) and Chukchi (CS) Seas experience different environments due primarily to a longer history of sea ice loss in the Beaufort Sea. Ecological differences have been identified as a possible reason for the generally poorer body condition and reproduction of Beaufort polar bears compared to those from the Chukchi, but the influence of exposure to other stressors remains unknown. We use molecular technology, quantitative PCR, to identify gene transcription differences among polar bears from the Beaufort and Chukchi Seas as well as captive healthy polar bears. We identified significant transcriptional differences among a priori groups (i.e., captive bears, SB 2012, SB 2013, CS 2013) for ten of the 14 genes of interest (i.e., CaM, HSP70, CCR3, TGFβ, COX2, THRα, T-bet, Gata3, CD69, and IL17); transcription levels of DRβ, IL1β, AHR, and Mx1 did not differ among groups. Multivariate analysis also demonstrated separation among the groups of polar bears. Specifically, we detected transcript profiles consistent with immune function impairment in polar bears from the Beaufort Sea, when compared with Chukchi and captive polar bears. Although there is no strong indication of differential exposure to contaminants or pathogens between CS and SB bears, there are clearly differences in important transcriptional responses between populations. Further investigation is warranted to refine interpretation of potential effects of described stress-related conditions for the SB population.

Polar Biology↗

USGS2015

Enhanced biological processes associated with alopecia in polar bears ( Ursus maritimus )

Populations of wildlife species worldwide experience incidents of mass morbidity and mortality. Primary or secondary drivers of these events may escape classical detection methods for identifying microbial insults, toxin exposure, or additional stressors. In 2012, 28% of polar bears sampled in a study in the southern Beaufort Sea region of Alaska had varying degrees of alopecia that was concomitant with reduced body condition. Concurrently, elevated numbers of sick or dead ringed seals were detected in the southern Beaufort, Chukchi, and Bering seas in 2012, resulting in the declaration of an unusual mortality event (UME) by the National Oceanic and Atmospheric Administration (NOAA). The primary and possible ancillary causative stressors of these events are unknown, and related physiological changes within individual animals have been undetectable using classical diagnostic methods. Here we present an emerging technology as a potentially guiding investigative approach aimed at elucidating the circumstances responsible for the susceptibility of certain polar bears to observed conditions. Using transcriptomic analysis we identified enhanced biological processes including immune response, viral defense, and response to stress in polar bears with alopecia. Our results support an alternative mechanism of investigation into the causative agents that, when used proactively, could serve as an early indicator for populations and species at risk. We suggest that current or classical methods for investigation into events of unusual morbidity and mortality can be costly, sometimes unfocused, and often inconclusive. Advances in technology allow for implementation of a holistic system of surveillance and investigation that could provide early warning of health concerns in wildlife species important to humans.

Science of the Total Environment↗

USGS2020

Brown Bear (Ursus arctos; North America)

This chapter comprises the following sections: names, taxonomy, subspecies and distribution, descriptive notes, habitat, movements and home range, activity patterns, feeding ecology, reproduction and growth, behavior, parasites and diseases, status in the wild, and status in captivity.

Book chapter↗

USGS2020

Polar Bear (Ursus maritimus)

Book chapter↗

USGS2017

Performance and retention of lightweight satellite radio tags applied to the ears of polar bears ( Ursus maritimus )

Background Satellite telemetry studies provide information that is critical to the conservation and management of species affected by ecological change. Here we report on the performance and retention of two types (SPOT-227 and SPOT-305A) of ear-mounted Argos-linked satellite transmitters (i.e., platform transmitter terminal, or PTT) deployed on free-ranging polar bears in Eastern Greenland, Baffin Bay, Kane Basin, the southern Beaufort Sea, and the Chukchi Sea during 2007–2013. Results Transmissions from 142 out of 145 PTTs deployed on polar bears were received for an average of 69.3 days. The average functional longevity, defined as the number of days they transmitted while still attached to polar bears, for SPOT-227 was 56.8 days and for SPOT-305A was 48.6 days. Thirty-four of the 142 (24%) PTTs showed signs of being detached before they stopped transmitting, indicating that tag loss was an important aspect of tag failure. Furthermore, 10 of 26 (38%) bears that were re-observed following application of a PTT had a split ear pinna, suggesting that some transmitters were detached by force. All six PTTs that were still on bears upon recapture had lost the antenna, which indicates that antenna breakage was a significant contributor to PTT failure. Finally, only nine of the 142 (6%) PTTs—three of which were still attached to bears—had a final voltage reading close to the value indicating battery exhaustion. This suggests that battery exhaustion was not a major factor in tag performance. Conclusions The average functional longevity of approximately 2 months for ear-mounted PTTs (this study) is poor compared to PTT collars fitted to adult female polar bears, which can last for several years. Early failure of the ear-mounted PTTs appeared to be caused primarily by detachment from the ear or antenna breakage. We suggest that much smaller and lighter ear-mounted transmitters are necessary to reduce the risk of tissue irritation, tissue damage, and tag detachment, and with a more robust antenna design. Our results are applicable to other tag types (e.g., iridium and VHF systems) and to research on other large mammals that cannot wear radio collars.

Animal Biotelemetry↗

USGS2004

Modeling the effects of human activity on Katmai brown bears (Ursus arctos) through the use of survival analysis

Brown bear-human interactions were observed in 1993, 1995, and 1997 at Kulik River in Katmai National Park and Preserve, Alaska. We analyzed these interactions using survival analysis, creating survival curves for the time that bears remained on the river in the presence, and absence, of human activity. Bear-only survival curves did not vary significantly between years (p = 0.067). Ninety-seven percent of bears left the river within 70 minutes of arrival in all years. Temporal patterns of bear activity were unaffected by the presence of humans as long as the bears did not share river zones with humans (p = 0.062 to p = 0.360). When people and bears did not share river zones, 38.6% (1993), 36.0% (1995), and 37.0% (1997) of bears remained on the river for at least 10 minutes after arrival. In contrast, when people and bears shared river zones, fewer bears remained on the river after the first 10 minutes, with 28.6% (1993), 25.0% (1995), and 32.6% (1997) observed in each year. We conclude that human activity displaced 26.0% (1993), 30.5% (1995), and 12.0% (1997) of the bears using the river, which otherwise would likely have remained longer. Over the three years of study, habituation to human activity may account for observed changes in bears' use of the river.

Alaska↗

USGS2015