Polar Bears In Depth
Survival
Page 4 of 5
FIGURE 27.10. Broken upper jaw of a large male polar bear captured in the Beaufort Sea in autumn 1999. Because they rely on strong jaws to catch and hold large prey animals, such injuries are probably fatal to polar bears. SOURCE: Photo by Steven C. Amstrup. Click image to enlarge.
Injuries to polar bear's mouth parts also may not be immediately fatal, but they probably are deadly in the long run. Despite capture of thousands of polar bears worldwide, confirmed observations of mended jaws or survival of polar bears with broken jaws are rare or lacking. The long penetrating canine teeth are the polar bear's most important trophic appendage and are critical to holding and killing large prey. Polar bears usually cannot switch to a diet of smaller food particles, and a broken jaw may simply reduce hunting efficiency below the survival threshold. I captured an emaciated but very large male polar bear one autumn when he should have been near his maximum weight. His weight was less than half that of similar-size males at that time. He seemed to be fit and his teeth were in excellent shape. On examination, however, we discovered that his maxilla was broken through (Fig. 27.10), and there was a pronounced gap in his palate. The front portion of his upper jaw was attached only by the skin and musculature of his lips. His ability to bite and hold large prey was seriously compromised. How this injury was sustained is not clear. He has not been recaptured, and given the bear's lean state just before the harshest season of the year, I suspect he did not survive the winter.
In addition to trauma of various kinds, an array of maladies occurs at low frequencies in polar bears just as they do with other wild and domestic mammals including humans. For example, a very large male in the Beaufort Sea died of gastric dilatation and volvulus (Amstrup and Nielsen 1989). This is a condition in which the alimentary organs, including the stomach and much of the intestine, rotate around the mesentaries that support those structures in the abdominal cavity. Blood supply is cut off, resulting in edema, shock, and rapid death. This is a phenomenon common in large, deep-chested dogs and in bears in zoos. Another bear apparently died as a result of occlusion of the bile duct by numerous large gall-stones (S. C. Amstrup unpublished data).
Reported diseases and parasites of polar bears are few. In 21 years of research in Alaska, I have not seen any evidence of ectoparasites. In an extensive review of ursid parasites, Rogers and Rogers (1976) found that seven endoparasites had been reported in polar bears. Only Trichinella spp., however, had been observed in wild animals. The three species of nematode and three species of cestodes that had been reported in captive polar bears had not occurred in the wild. Trichinella can be quite common in polar bears and has been observed throughout their range. Concentrations of this parasite in some tissues can be high, but infections are not normally fatal (Rausch 1970; Dick and Belosevic 1978; Larsen and Kjos-Hanssen 1983; Taylor et al. 1985). Arctic foxes (Alopex lagopus) are common carriers of rabies and they routinely interact with polar bears. However, only one instance of rabies has been confirmed in a polar bear (Taylor et al. 1991). Although polar bears are not immune to diseases and parasites, they seem to be plagued by fewer of these problems than most terrestrial mammals.
In addition to trauma of various kinds, an array of maladies occurs at low frequencies in polar bears just as they do with other wild and domestic mammals including humans. For example, a very large male in the Beaufort Sea died of gastric dilatation and volvulus (Amstrup and Nielsen 1989). This is a condition in which the alimentary organs, including the stomach and much of the intestine, rotate around the mesentaries that support those structures in the abdominal cavity. Blood supply is cut off, resulting in edema, shock, and rapid death. This is a phenomenon common in large, deep-chested dogs and in bears in zoos. Another bear apparently died as a result of occlusion of the bile duct by numerous large gall-stones (S. C. Amstrup unpublished data).
Reported diseases and parasites of polar bears are few. In 21 years of research in Alaska, I have not seen any evidence of ectoparasites. In an extensive review of ursid parasites, Rogers and Rogers (1976) found that seven endoparasites had been reported in polar bears. Only Trichinella spp., however, had been observed in wild animals. The three species of nematode and three species of cestodes that had been reported in captive polar bears had not occurred in the wild. Trichinella can be quite common in polar bears and has been observed throughout their range. Concentrations of this parasite in some tissues can be high, but infections are not normally fatal (Rausch 1970; Dick and Belosevic 1978; Larsen and Kjos-Hanssen 1983; Taylor et al. 1985). Arctic foxes (Alopex lagopus) are common carriers of rabies and they routinely interact with polar bears. However, only one instance of rabies has been confirmed in a polar bear (Taylor et al. 1991). Although polar bears are not immune to diseases and parasites, they seem to be plagued by fewer of these problems than most terrestrial mammals.