The effects of forest fires on polar bear maternity denning habitat in western Hudson Bay

The effects of forest fires on polar bear (Ursus maritimus) maternity denning habitat in western Hudson Bay were determined by comparing the physical characteristics of 48 burned and 101 unburned maternity den sites from September 2001 to October 2003. Fire significantly altered vegetation composition and increased the depth of the active layer, resulting in a decrease in the stability of den sites, the collapse of dens, and degradation of the surrounding habitat. Although bears investigated burned areas, analysis of mark and recapture data, satellite telemetry, radio-telemetry, and field observations all demonstrated that bears did not use burned areas for denning. While peat denning habitat is likely not limiting at this time, the re-use and occupancy of peat den sites during the summer may be an important means of energy conservation for pregnant female bears in western Hudson Bay. Increased energy expenditures in association with increased search times for suitable den sites and the excavation of new dens can potentially affect reproductive success. Predicted increases in forest fire activity as a result of climate change, along with the long-term recovery of denning habitat may reduce the amount of suitable denning habitat in the future. Resource managers need to be aware of the possibility of a shift in the distribution of denning bears and further loss of maternity denning habitat in western Hudson Bay.     

Selection of maternity dens by female polar bears in western Hudson Bay,Canada and the effects of human disturbance

We deployed 19 satellite radio collars on adult female polar bears (Ursus maritimus) in western Hudson Bay to study how pregnant females select maternity-den sites and the degree to which human disturbance might influence this process. To eliminate the possibility that being handled while pregnant might influence the final choice of a suitable site, the collars were attached 1 year before the females were expected to select dens. Our results indicated that pregnant females moved inland and selected an area to den shortly after coming ashore in the summer and remained there if not disturbed. We analyzed 24 years of consecutive data (1979–2002) to examine whether disturbance of pregnant females in the denning area in the autumn affected litter size or mass of cubs the following spring. We defined three levels of disturbance (none—bear not seen; low—bear seen but not handled; high—bear seen and handled), and found that disturbance had no effect on either litter size or the mass of male cubs. However, we did find that females handled in the autumn had significantly lighter female cubs than females that were not seen. Our disturbance of pregnant females occurred in August and September, which is only a few months prior to parturition; it is not known what the effects of disturbance might be in late October or early November, closer to the time when cubs are born.     

Functional responses in polar bear habitat selection

Habitat selection may occur in situations in which animals experience a trade-off, e.g. between the use of habitats with abundant forage and the use of safer retreat habitats with little forage. Such trade-offs may yield relative habitat use conditional on the relative availability of the different habitat types, as proportional use of foraging habitat may exceed proportional availability when foraging habitat is scarce, but be less than availability when foraging habitat is abundant. Hence, trade-offs in habitat use may result in functional responses in habitat use (i.e. change in relative use with changing availability). We used logistic and log-linear models to model functional responses in female polar bear habitat use based on satellite telemetry data from two contiguous populations; one near shore inhabiting sea ice within fjords, and one inhabiting pelagic drift ice. Open ice, near the ice edge, is a highly dynamic habitat hypothesised to be important polar bear habitat due to high prey availability. In open ice-polar bears may experience a high energetic cost of movements and risk drifting away from the main ice field (i.e. trade off between feeding and energy saving or safety). If polar bears were constrained by ice dynamics we therefore predicted use of retreat habitats with greater ice coverage relative to habitats used for hunting. The polar bears demonstrated season and population specific functional responses in habitat use, likely reflecting seasonal and regional variation in use of retreat and foraging habitats. We suggest that in seasons with functional responses in habitat use, polar bear space use and population distribution may not be a mere reflection of prey availability but rather reflect the alternate allocation of time in hunting and retreat habitats.     

Observation of a polar bear with rabies

On 1 November 1989 the first confirmed case of rabies in a polar bear (Ursus maritimus) was encountered by Inuit hunters in the vicinity of Cape Kendall, Southampton Island, Northwest Territories (Canada). The adult male polar bear had posterior paralysis. Rabies was detected by mouse inoculation and a positive immunoperoxidase reaction on spinal cord and Gasserian ganglion from the bear. Histologic lesions in the lumbar region of the spinal cord were consistent with the posterior paralysis. The impact of rabies on the population dynamics of polar bears probably is minimal. Rabies in polar bears constitutes a potential health hazard for polar bear hunters.     

Biomechanical consequences of rapid evolution in the polar bear lineage

The polar bear is the only living ursid with a fully carnivorous diet. Despite a number of well-documented craniodental adaptations for a diet of seal flesh and blubber, molecular and paleontological data indicate that this morphologically distinct species evolved less than a million years ago from the omnivorous brown bear. To better understand the evolution of this dietary specialization, we used phylogenetic tests to estimate the rate of morphological specialization in polar bears. We then used finite element analysis (FEA) to compare the limits of feeding performance in the polar bear skull to that of the phylogenetically and geographically close brown bear. Results indicate that extremely rapid evolution of semi-aquatic adaptations and dietary specialization in the polar bear lineage produced a cranial morphology that is weaker than that of brown bears and less suited to processing tough omnivorous or herbivorous diets. Our results suggest that continuation of current climate trends could affect polar bears by not only eliminating their primary food source, but also through competition with northward advancing, generalized brown populations for resources that they are ill-equipped to utilize.     

Acute gastric dilatation and volvulus in a free-living polar bear

A large, adult male polar bear (Ursus maritimus) was found dead on a barrier island north of Prudhoe Bay, Alaska (USA), in June 1987. There were no external signs of trauma. A twisted distended stomach, distinctive parenchymal and fascial congestion, and significant difficulty in repositioning the anterior abdominal organs, indicated that gastric dilatation-volvulus (GDV) was the proximate cause of death. Polar bears frequently consume large quantities of food at one time and have large stomachs that are well adapted to periodic gorging. The scarcity of food in winter and early spring, combined with voluntary fasting and protracted vigorous activity during the breeding season in late spring may have predisposed this bear to GDV. The relationship between GDV and postprandial exercise emphasizes the need for a better understanding of how the present human invasion of arctic habitats may influence polar bear activities.     

Two decades of biomonitoring polar bear health in Greenland: a review

Background

Different animal models are used as fracture models in orthopaedic research prior to implant use in humans, although biomechanical forces can differ to a great extend between species due to variable anatomic conditions, particularly with regard to the gait. The rabbit is an often used fracture model, but biomechanical data are very rare. The objective of the present study was to measure axial forces, bending moments, and bending axis directly in the rabbit tibia in vivo. The following hypothesis was tested: Axial forces and bending moments in the mid-diaphysis of rabbit tibia differ from other experimental animals or indirectly calculated data.

Methods

A minifixateur system with 4 force sensors was developed and attached to rabbit tibia (n = 4), which were subsequently ostectomised. Axial forces, bending moments and bending angles were calculated telemetrically during weight bearing in motion between 6 and 42 days post operation.

Results

Highest single values were 201% body weight [% bw] for axial forces and 409% bw cm for bending moments. Whereas there was a continous decrease in axial forces over time after day 10 (P = 0.03 on day 15), a decrease in bending moments was inconsistent (P = 0.03 on day 27). High values for bending moments were frequently, but not consistently, associated with high values for axial forces.

Conclusion

Axial forces in rabbit tibia exceeded axial forces in sheep, and differed from indirectly calculated data. The rabbit is an appropriate fracture model because axial loads and bending moments in rabbit tibia were more closely to human conditions than in sheep tibia as an animal model.     

Chemical characterization of milk oligosaccharides of the polar bear, Ursus maritimus

Two trisaccharides, three tetrasaccharides, two pentasaccharides, one hexasaccharide, one heptasaccharide, one octasaccharide and one decasaccharide were isolated from polar bear milk samples by chloroform/methanol extraction, gel filtration, ion exchange chromatography and preparative thin-layer chromatography. The oligosaccharides were characterized by 1H-NMR as follows: the saccharides from one animal: Gal(alpha1-3)Gal(beta1-4)Glc (alpha3'-galactosyllactose), Fuc(alpha1-2)Gal(beta1-4)Glc (2'-fucosyllactose), Gal(alpha1-3)[Fuc(alpha1-2)]Gal(beta1-4)Glc (B-tetrasaccharide), GalNAc(alpha1-3)[Fuc(alpha1-2)]Gal(beta1-4)Glc (A-tetrasaccharide), Gal(alpha1-3)Gal(beta1-4)GlcNAc(beta1-3)Gal(beta1-4)Glc, Gal(alpha1-3)[Fuc(alpha1-2)]Gal(beta1-4)GlcNAc(beta1-3)Gal(beta1-4)Gl c, Gal(alpha1-3)Gal(beta1-4)GlcNAc(beta1-3)[Gal(alpha1-3)Gal(beta1-4)Glc NAc(beta1-6)]Gal(beta1-4)Glc; the saccharides from another animal: alpha3'-galactosyllactose, Gal(alpha1-3)Gal(beta1-4)[Fuc(alpha1-3)]Glc, A-tetrasaccharide, GalNAc(alpha1-3)[Fuc(alpha1-2)]Gal(beta1-4)[Fuc(alpha1-3)]Glc (A-pentasaccharide), Gal(alpha1-3)Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc(beta1-3)Gal(beta1-4)Gl c, Gal(alpha1-3)Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc(beta1-3)Gal(beta1-4)[F uc(alpha1-3)]Glc (difucosylheptasaccharide) and Gal(alpha1-3)Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc(beta1-3)?Gal(alpha1-3) Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc(beta1-6)?Gal(beta1-4)Glc (difucosyldecasaccharide). Lactose was present only in small amounts. Some of the milk oligosaccharides of the polar bear had alpha-Gal epitopes similar to some oligosaccharides in milk from the Ezo brown bear and the Japanese black bear. Some milk oligosaccharides had human blood group A antigens as well as B antigens; these were different from the oligosaccharides in Ezo brown and Japanese black bears.     

Differences in oligosaccharide pattern of a sample of polar bear colostrum and mid-lactation milk

Although the concentrations of carbohydrate in the colostrum and in the mid-lactation milk of polar bear (Ursus maritimus) were similar, the oligosaccharide patterns differed. The colostrum sample contained Neu5Ac(α2-3)Gal(β1-4)Glc (3′-N-acetylneuraminyllactose), GalNAc(α1-3)[Fuc(α1-2)]Gal(β1-4)Glc (A-tetrasaccharide), Fuc(α1-2)Gal(β1-4)Glc (2′-fucosyllactose) and Gal(β1-4)Glc (lactose). The mid-lactation milk contained Gal(α1-3)[Fuc(α1-2)]Gal(β1-4)[Fuc(α1-3)]Glc (B-pentasaccharide), GalNAc(α1-3)[Fuc(α1-2)]Gal(β1-4)[Fuc(α1-3)]Glc (A-pentasaccharide), Gal(α1-3)[Fuc(α1-2)]Gal(β1-4)Glc (B-tetrasaccharide), A-tetrasaccharide, Gal(α1-3)Gal(β1-4)[Fuc(α1-3)]Glc (3-fucosylisoglobotriose), Gal(α1-3)Gal(β1-4)Glc (isoglobotriose) and lactose. The dominant saccharides in the colostrum were 3′-N-Acetylneuraminyllactose and lactose, whereas isoglobotriose was the dominant saccharide in the mid-lactation milk in which lactose was only a minor component. Isoglobotriose, which had previously been found to be a dominant saccharide in mature milk from the Ezo brown bear, the Japanese black bear and the polar bear, was not found in the polar bear colostrum.     

Treatment of an acquired abdominal hernia in a polar bear (Thalarctos maritimus).

A heart rate radio-transmitter was surgically implanted in the abdomen of a captive adult male polar bear (Thalarctos maritimus), but within five weeks a purulent discharge was observed at the incision site. The transmitter was surgically removed along with many fragments of the fractured encapsulation material. The skin incision healed, but a large hernia remained. Repeated localized trauma to the hernia sac necessitated surgical repair.