Mammals are a mostly drab bunch. Due to camouflage, a nocturnal lifestyle and other evolutionary demands, dull and earthy tones reign supreme. There are a few notable exceptions. When mandrills become excited, the monkeys' rumps turn shades of ruby and bright blue, an effect not unlike melted crayon wax.
But bears, by and large, stick to the muted program. Even North American black bears, whose name belies their true variations, keep to blacks or brown shades, with a just a handful of those bears sporting dirty white or bluish-gray coats.
Then there is the panda bear.
Though pandas keep to stark blacks and whites, their patterns are famous. Their iconic image has served as an Olympic mascot and as an international symbol of conservation. In addition, their markings were the inspiration behind a catchy rap jingle.
But simply because something was ubiquitous did not mean it was well-understood.
Why, for example, are pandas black and white? The authors of a new study on the panda think they might have the answer: Panda patterns serve as a combination of communication and camouflage, a group of biologists wrote recently in the journal Behavioral Ecology.
The purpose of the pandas' black limbs, black ears, black eye patches and white bodies was a particular curiosity to these scientists at the University of California at Davis and California State University at Long Beach.
"Understanding why the giant panda has such striking coloration has been a long-standing problem in biology that has been difficult to tackle because virtually no other mammal has this appearance, making analogies difficult," Tim Caro, a biologist in Wildlife, Fish and Conservation Biology department on the Davis campus, said in a news release.
Caro knows a bit about animal color. He made a compelling case that zebras evolved stripes as a defense against biting flies in a book published in December, and has also investigated the colors of skunks and coconut crabs.
The biologists reached their conclusion by combing through photographs of many different animal coats, representing 195 other land-dwelling carnivores as well as nearly 40 different types of bears. They isolated fur colors over different parts of the body: back, legs, ears and head, and also divided the animals' faces into separate regions.
"The breakthrough in the study was treating each part of the body as an independent area," Caro said.
The scientists compared the panda patterns to animals living in a variety of environmental and geographic conditions, including snow cover, shade, sun glare and temperature. Because the study was comparative in nature, it had a few limitations, as the authors noted: "It is always possible that a patch of fur has evolved for a different purpose than in other carnivores."
Animals that grew winter coats, the scientists found, had significantly lighter fur in the cold. But there were few relationships between eye markings and an environment's brightness - which is to suggest that dark patches around the panda eyes did not come about as a defense to the sun along the lines of NFL eyeblack.
Two environmental measures, forest shade and snow, appeared to influence the panda's coat.
Pandas, unlike other bears, cannot slumber through the winter. (Blame the poor nutritional value of bamboo, as the scientists pointed out in the paper, as the reason pandas "cannot lay down sufficient fat reserves to hibernate.") Instead, the creatures must constantly prowl the Chinese wilds for their bamboo fix.
This means that their surroundings change relatively rapidly between light snow and dark forest shade. The pattern, then, is something of a camouflage compromise. Pandas' white bodies and heads blend into snow, whereas the black limbs can disappear into the shadows of trees and vegetation.
As for the panda faces, the scientists said they found "links between contrasting ears and pugnacity," which is to say that the bears' black ears may serve as a warning to would-be predators. The eye contrast, too, could work similarly as aggression displays.
But there was another possible reason for the eye marks. Carnivores active during the daytime tended to have somewhat darker coloration around the eyes, suggesting that other animals were meant to see the patches, though the evidence for this was "weak."
More compelling was a 2008 study in which two young pandas identified subtle differences in artificial eye-mask patterns. The panda pair recalled the different masks a year later. The distinctive face markings might work a bit like panda nametags, then, allowing individual bears to recognize one another.