Polar Bears In Depth
Feeding Habits
Page 1 of 3
FIGURE 27.6. Ringed seal (Phoca hispida), named for the ringlike pattern in the fur. Ringed seals, which weigh <100 kg, make up the greatest portion of the polar bear diet worldwide. SOURCE: Photo by Steven C. Amstrup. Click image to enlarge.
The polar bear is more predatory than other bears and is the apical predator of the arctic marine ecosystem. Polar bears prey heavily throughout their range on ringed seals (Phoca hispida) (Fig. 27.6) and, to a lesser extent, bearded seals (Erignathus barbatus) (Fig. 27.7). Ringed seals apparently have been a principal food of polar bears for a significant portion of their coevolutionary history and ringed seal behaviors appear to be oriented around avoidance of polar bear predation. Stirling (1977) contrasted the behavioral ecology of ringed seals and Weddell seals (Leptonychotes weddelli). Steady predation pressure from polar bears may have led ringed seals to use subnivian birthing lairs and to interrupt spring and summer basking with frequent periods of scanning their surroundings for predators. Weddell seals, on the other hand, evolved in the Antarctic system, where surface predators are absent. They give birth unsheltered on the surface of the sea ice, and they are so ambivalent about activities on the ice surface that human researchers often can walk right up to them for study purposes (Stirling 1977).
FIGURE 27.6. Ringed seal (Phoca hispida), named for the ringlike pattern in the fur. Ringed seals, which weigh <100 kg, make up the greatest portion of the polar bear diet worldwide. SOURCE: Photo by Steven C. Amstrup.
Although seals are their primary prey, polar bears also have been known to kill much larger animals such as walruses (Odobenus rosmarus) and belugas (Delphinapterus leucas) (Stirling and Archibald 1977; Kiliaan et al. 1978; Smith 1980, 1985; Lowry et al. 1987; Calvert and Stirling 1990). The heaviest prey may be taken mainly by large male polar bears (Stirling and Derocher 1990), and unusual circumstances may be required. Nonetheless, in some areas and under some conditions, alternate prey may be quite important to polar bear sustenance. Stirling and Øritsland (1995) suggested that in areas where the estimated numbers of ringed seals are proportionately reduced relative to numbers of polar bears, other prey species were being substituted.
FIGURE 27.6. Ringed seal (Phoca hispida), named for the ringlike pattern in the fur. Ringed seals, which weigh <100 kg, make up the greatest portion of the polar bear diet worldwide. SOURCE: Photo by Steven C. Amstrup.
Although seals are their primary prey, polar bears also have been known to kill much larger animals such as walruses (Odobenus rosmarus) and belugas (Delphinapterus leucas) (Stirling and Archibald 1977; Kiliaan et al. 1978; Smith 1980, 1985; Lowry et al. 1987; Calvert and Stirling 1990). The heaviest prey may be taken mainly by large male polar bears (Stirling and Derocher 1990), and unusual circumstances may be required. Nonetheless, in some areas and under some conditions, alternate prey may be quite important to polar bear sustenance. Stirling and Øritsland (1995) suggested that in areas where the estimated numbers of ringed seals are proportionately reduced relative to numbers of polar bears, other prey species were being substituted.