A new study by American researchers reveals giant pandas are capable of distinguishing colors from shades of gray. Color vision could be useful to pandas in the wild by helping them recognize healthy bamboo patches from brown and dying ones.

Study leader Angela Kelling, a graduate researcher at Georgia Institute of Technology and Zoo Atlanta, said color vision is documented in domesticated animals, like cats and dogs, and in primates, but not in carnivores.

Kelling and her co-researchers decided to study color vision in pandas because their cognitive and sensory abilities aren't yet well understood, and "we have such a rare opportunity having them at Zoo Atlanta," she said.

Most mammals are dichromatic, or can distinguish only color and gray, which Kelling says is most likely the case with giant pandas.

"They don't see (colors) the same way we do, but they are able to distinguish them as a separate color," Kelling said.

Dichromatism is usually attributed to the presence of only two cones cells in the retina of the eye. These cells are sensitive to higher-intensity light, with different types allowing for the detection of certain colors.

Humans and many other primates have three cones, and so are trichromatic.

Kelling showed the pandas three PVC pipes each hanging under a piece of paper to test their color-sensing abilities. Two of the pipes were hung under paper that was colored one of 18 shades of gray. The third hung under paper colored one of five shades of three different colors -- red, blue and green.

If the pandas pushed the pipe under the colored paper, they received a treat. If they pushed the other pipes -- no treat. The colors and shades of gray were mixed up through the trial.

Color vision was confirmed if the pandas pressed the colored pipe for 80 percent of the trials in three consecutive sessions. Lun Lun, the female, passed for all three colors, while Yang Yang, the male, passed for two because a tooth problem prevented him from participating in the third trial.

"While this study shows that giant pandas have some color vision, it wasn't conclusive as to what level of color vision they have," Kelling said. "From this study, we can't tell if the pandas can tell the difference between colors themselves, like red from blue or blue from green. But we can see that they can determine if something is gray or colored."

(Xinhua News Agency October 19, 2006)