Science First Look

Why are pandas black and white? Science finds clues.

The giant panda's distinct coloring is loved by wildlife enthusiasts, but researchers have never had a satisfactory explanation as to what made their coloring pattern so unique – until now.

In February, US-born giant female panda Bao Bao walks at her new home, Chengdu Research Base of Giant Panda Breeding, in Chengdu, Sichuan province, China
China Daily via Reuters
|
Caption

Pandas, known all over the world for their unique black-and-white pattern, are one of nature's most unusual creatures. Their extremely limited bamboo diet and famed reluctance to breed put them on the brink of extinction for decades, leaving the endangered species lists only last year.

But despite the increased scientific scrutiny that comes with ecological vulnerability, the panda's strange color pattern remained a mystery. Other kinds of bears tend to sport solid, non-patterned colors, and scientists did not have a satisfactory explanation as to why the panda bear was so different. Now, however, researchers from University of California, Davis, and California State University, Long Beach think they may have solved the mystery, once and for all.

"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," said lead author Tim Caro, a professor in the UC Davis Department of Wildlife, Fish and Conservation Biology, in a statement. "The breakthrough in the study was treating each part of the body as an independent area."

The researchers found that while some areas of the panda were black instead of white, the black areas were not always black for the same reasons. In order to figure out what each part of the fur was for, they compared the panda to the coloring of 195 other carnivore species and 39 bear subspecies the bear is related to.

The researchers found "no compelling support for their fur color being involved in temperature regulation, disrupting the animal's outline, or in reducing eye glare," according to their study published in the journal Behavioral Ecology, which were all explanations put forward as potential solutions to the coloring problem. Instead, researchers discovered that the coloring could be tied to two main functions: crypsis (camouflage) and communication.

The researchers realized that, unlike some other types of bears, pandas have to be active year-round without hibernation. The scarceness of bamboo, the only food pandas are capable of digesting, means that pandas need to be able to cross a wide range of habitats in search of a meal, from dense, warm rainforests to snowy, mountainous regions. The white parts of their fur helps pandas to blend in with snowy surroundings, and the black portions help them hide in shady forests.

But the researchers also found that the black portions on the heads of the bears were not directly related to crypsis. Instead, their dark ears communicate aggressive warnings to potential predators, and their black eye patches may help them to be recognized by other bears as well as being signals warning against fellow panda competitors.

This isn't the first time this team of scientists has helped crack the code of a black-and-white fur coat. Last year, the researchers were involved in studies to challenge the longstanding notion that a zebra's stripes help it hide from predators. As Jason Thomson previously reported for The Christian Science Monitor:

Results from the work indicate that beyond 50 meters (about 164 feet) in daylight or 30 meters (about 98 feet) at twilight, when most predators hunt, the stripes are difficult for large carnivores to distinguish. On moonless nights, the distance drops to a mere 9 meters (about 29 feet).

In addition, the research concluded that on open plains, where zebras spend most of their time, lions could see the outline of zebras just as easily as that of similar-sized prey with fairly solid shading patterns.

If the conclusions of this research are correct, and stripes confer no advantage against predation, where did the idea come from, and is there any evidence to support it?

“The idea that stripes allowed zebras to blend into a background composed of tall stem enriched grasses is an old one that emerged from casual observations,” says leading zebra expert Daniel Rubenstein of Princeton University, in an email interview with The Christian Science Monitor.  “Until this study most evidence in support of this hypothesis has been anecdotal”.

The researchers involved in that study determined that the reason for the zebra's stripes likely has to do (at least partially) with the pattern's ability to repel flies.

But as far as the panda's coloring is concerned, it's case closed – at least for now, says panda study co-author Ted Stankowich, an assistant professor at CSU Long Beach.

"This really was a Herculean effort by our team, finding and scoring thousands of images and scoring more than 10 areas per picture from over 20 possible colors," said Dr. Stankowich in the statement. "Sometimes it takes hundreds of hours of hard work to answer what seems like the simplest of questions: Why is the panda black and white?"