ECOVIEWS: Why do animals turn white in Arctic, but not Antarctic?


Q: Why do so many animals turn white in winter or stay white all year at the North Pole but not at the South Pole? Wouldn’t the same camouflage conditions apply to both? Will global warming affect these color patterns?

A: Throughout the animal kingdom, in circumstances where being unseen or at least inconspicuous is beneficial, camouflage is critical for prey and predators alike. Clearly, both polar regions have plenty of snow to make a white body effective camouflage under certain conditions. However, the Arctic includes vast areas of terrestrial habitats, such as Alaska, Canada and Russia, whereas Antarctica has no physical connection to another continent. Consequently, during the summer (even without the effects of climate change), 90 percent of the Arctic is not frozen, whereas more than 90 percent of Antarctica is permanently covered with ice and snow. The ecological consequence is that the Arctic has a variety of strictly terrestrial mammals and Antarctica has none. Therefore, the strategies of native inhabitants in the two regions vary greatly, which means some animals at the North Pole must change their appearance seasonally to be camouflaged.

Penguins, which are found at the South Pole but not the North Pole, are primarily black and white. Being solid white would serve little advantage to an animal that has no land predators to hide from and has to dive for fish in dark waters. Most penguins have a dark back and lighter colored front. That countershading helps these flightless birds be inconspicuous when observed from above or below while swimming. Likewise, there are no terrestrial predators that need to be white so they can sneak up on unsuspecting prey.

The tactics for avoiding predators and catching prey are entirely different in the Arctic. The Arctic is defined as regions of tundra and permanent ice cover above the treeline in North America, Europe and Asia. Being seen would be a disadvantage for prey animals like Arctic hares (found from northeastern Canada to Greenland) or snowshoe hares (found from Alaska through southern Canada and the northern United States). They fare best in a brown coat during warm months when the soil surface is visible. In the cold Arctic portion of their geographic ranges, when autumn snow begins to whiten the surroundings, white is the best color for a coat. Seasonal color change from brown to white also occurs in some non-Arctic species. For example, whitetail jackrabbits do not occur in the Arctic, but they are found in northern portions of the western United States and into southern Canada. In the coldest and snowiest parts of their geographic range, they turn white in winter.

The Arctic fox adopts a similar seasonal color change tactic for two reasons. First, Arctic foxes do not want to be seen by rodents and hares, which are the prey of these wily predators. Second, Arctic foxes often scavenge in winter, dining on the remains of seal or fish left by polar bears. Presumably, polar bears would eat a fox as well, so having a wintertime camouflage of pure white (or sometimes bluish-gray) fur works well for the fox. In summer, brown becomes the fashion, as with the hares and many other Arctic mammals.

The white coats of Arctic animals have long been popular in the fashion industry, and a magnificent white ermine coat was once the most elegant of winter apparel. A white ermine, with only a black tail tip, must be caught during the Arctic winter. In the summer the ermine turns mahogany brown. Members of the weasel family, ermine are best known among wildlife biologists as short-tail weasels. For some reason, I have never heard of anyone boasting about the sumptuous weasel coat she wore to the royal ball.

One interpretation of scientific predictions about climate change in polar regions is that white might not continue to be a necessary part of the wardrobe of Arctic animals. But how they will adjust to this change is unknown.

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