ID polar bears Essay
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Stirling’s theme (p. 3) was that polar bears should be studied as part of the arctic environment, influencing other species, such as seals (the polar bear’s main source of food), and changing their behavior to adapt to changes in regions of the arctic. Because the polar bear is a “solitary predator” (p. 3), individual bears have had different experiences. Thus, one cannot generalize observations of a single bear to other bears.
It was only a couple of decades prior to publication of Stirling’s book (1988) that techniques were developed to allow studying large samples of bears and following their development in repeated studies of the same bears.
First, a method was developed for immobilizing a bear by shooting a dart containing Telazol from a helicopter (pp. 53-57), making it possible to accurately assess the physical characteristics of male and female bears of different ages. By attaching radio collars to the immobilized bears, the same bears could be recaptured and studied over time.
Unless one wanted to risk becoming polar bear food, the bear had to be returned to its place of capture before becoming mobile. Second, to study the behavior of large numbers of bears for extended periods of time, Stirling initiated the use of shacks hundreds of miles above sea ice so the bears could be observed with binoculars and telescopes (p. 114). These techniques made it possible for Stirling to provide the reader with information about all aspects of a polar bear’s life and environment. Scientific Tests II. Observing Polar Bear Behavior
Until 1973, the main way to observe the behavior of polar bears in their natural habitats (as opposed to observing temporarily immobilized bears) was to use a helicopter to follow walking bears until you lost their tracks (p. 113). Thus direct observations were limited to walking behavior. One could not directly observe potentially fascinating behaviors such as hunting, mating rituals, tending to cubs, or the many possible interactions of the bears with each other. Stirling thought it might be possible to directly observe polar bears for extended periods of time on the sea ice.
His initial test was to use an existing shack with a direct view of the sea ice, which was 640 feet above the sea on Caswell Tower. He and his wife used telescopes and binoculars to search for bears. After their second day at the shack, the fog lifted and they were able to watch the bears in daylight, which lasted 24 hours a day during the time of their trip, and they “collected 603 hours of observations, the most that had ever been done at that time, and . . . learned an immense amount about the behavior of undisturbed polar bears” (p. 114).
The success of the initial test generated the interest of other researchers, and the importance of being able to directly observe the day-to-day lives of polar bears cannot be over-stated. III. Implications of Time Cubs Spend with Mothers In most areas, after leaving the den, cubs remain with their mothers for two and half years (pp. 91, 120). Stirling concluded that the time was required for the cubs to learn to hunt by watching and imitating their mothers (p. 120). However, in an area of the Hudson Bay, about 40% of the cubs leave their mothers after a year and a half, and Ramsay (cited in Stirling, 1988, p.
90) questioned whether cubs kept by their mothers for less time had lower survival rates. He compared cubs still with their mothers with those of the same age but not with their mothers and found no differences. Stirling noted that the Hudson Bay differed from other areas because the weather was warmer, making it easier for cubs to break through the softer snowdrifts, that the area might have more seals (so there’s less competition with adult bears), and that the presence of large bearded seals resulted in leftovers for the cubs.
However, the finding raises the question of whether observation and imitation are required for cubs to learn to hunt. Human babies, for example, constantly see their parents and others walking, but walking is not attributable to observation and imitation (typically, babies first crawl and then pull themselves upright, regardless of whether they had seen other babies similarly engaged). Clearly cubs depend on their mothers to provide food, but it would be interesting to measure the time individual cubs with the same mothers actually spend watching her hunt and then assess the relationship between watching and later hunting skill.
IV. Oil Spills In the late 1970s, explorations for oil in the seas inhabited by polar bears increased, causing concern among researchers about oil spills (p. 148). Previous research demonstrated that oil contact could be fatal to sea otters and fur seals. In a test with polar bears, three went into a pool where oil had been spilled and they swam across it to reach the sea ice. There were no effects until the bears became cold and began to lick off the oil that had stuck to their fur. Two died of kidney failure, and the third recovered after treatment.
Despite typical protests from portions of the public about killing the bears, evidence that spilled oil caused the death of polar bears was required in efforts to change government policies and the practices of oil companies. Conclusions V. Sex Differences in Survival Rates Between 20% and 40% (depending on area) of cubs die during their first year (p. 137) and large percentages of “subadults” (bears who have left their mothers but are not yet adults) die before they are 5 or 6, when they become adults (p. 139).
Adults die at an average rate of 5% a year, their average age is 9-10 years, and most die by 15-18 years (p. 139). Beginning at adulthood, a greater percentage of male polar bears die each year than females. Stirling’s conclusion was that the main reason for this was male mortalities in their continuing battles with each other to mate with females (p. 139). However, he reached this conclusion ignoring findings presented elsewhere in the book of other plausible reasons. Because of the greater size of males (770 to over 1500 lbs. , vs. female weights between 330 and 550 lbs. , p.
23), they use up more energy than females when they walk (p. 144) and overheat more quickly than adult females and subadults when they run (p. 138). In the kind of hunting where a bear lies still until detecting a seal under the snow and then stands on his or her hind legs and attacks (p. 120), total time engaged in this activity was similar for males and females (p. 122). However, the average individual still-hunt time was longer for males than females (65-70 and 35-40 minutes for males and females respectively) – and, despite the shorter time, females were successful more often than males.
However, usually, the male’s greater strength allows him to choose the best hunting areas and to prevent adult females and subadults from using these areas and to snatch seals they may have caught. As a result, adult males are better-nourished and in better physical condition than females – who nonetheless have longer survival rates than males. Especially because some of these patterns also occur in humans, for example, women generally are smaller, have greater endurance, and their greater longevity has not been attributed to male physical fighting, Stirling’s conclusion, noted above, is not convincing. VI.
Male Play Fighting When observing bears six months before the breeding season, researchers have observed that adult males regularly engaged in a form of fighting that appears the same as the fighting over females that cause severe injuries and death – except that they do not harm each other (p. 167). Stirling concluded that the most likely explanation was that the behavior provided an opportunity to practice and improve fighting skills, having “survival value” during actual fighting (p. 168). The conclusion is problematic, however, because when these bears actually fight, all would have had the same opportunity to improve.
Stirling related almost all polar bear behaviors to survival, despite noting, for example, that while cubs are with their mothers, who are hunting, they typically engage in playing, including play fighting, with their siblings, and even when there are no siblings, individual cubs find ways to play (p. 121). Certainly, both within and between species, the fittest survive (Darwin’s theory), but maybe the play fighting of the male bears is just that – play. It’s hard to perceive survival value in the “conspicuous consumption” of people or, for that matter, in the common observation of kittens chasing their tails.
VII. The Life of a Polar Bear Based on his own observations and the observations of other researchers, Stirling concluded the “entire existence [of polar bears] is built around hunting and the conservation of energy” (p. 116). Because access to seals and other edible animals is seasonal, the bears need to be consumed by hunting during plentiful times and conserve their energy to survive times of scarcity. A pregnant adult must store enough body fat to last until she comes out of her den with her cubs, a period that can last up to 8 months, depending on the area (p. 84).
It is not uncommon for these mothers to face near-starvation, sometimes eating a cub or two (p. 137). Since the typical female spends her entire adult life pregnant and then caring for her cubs up to two and a half years, and is at a disadvantage relative to males in catching seals, one can’t help but ask: Is survival worth the cost? Because males use up more energy than females, they too need to conserve, but their success at hunting leaves them well nourished and in good condition. Evaluation With the exceptions noted above regarding some of Stirling’s conclusions, there is nothing I disliked about the book.
So far as what I liked, first Sterling thinks and writes about polar bears in a way that is neither “sappy” nor coldly clinical. While he supports the conservation of the bears and protecting their environments from industrial contamination, he also is involved in research on overpopulation in particular areas, so sensible hunting limitations (not universal bans) can be set. Perhaps to the dismay of animal activists, he is opposed to overpopulation that makes the hungry bears a danger to humans. In brief, one comes away thinking that polar bears are fascinating, though more than occasionally, not very nice animals.
Second, many books about science are written by science writers because many scientists are not able to provide clear explanations of their own work and the work of others. Unlike science writers who do not specialize in particular areas of science, a good scientist also is thoroughly up to date on research in his or her own area of specialization. Stirling is a scientist himself and provided clear and up-to-date explanations of his own work and the work of other researchers. Third, Guravich’s photographs are spectacular. They depict all aspects of the polar bear – sometimes appearing majestic, playful, cuddly, menacing, or plain mean.