Mystery Solved: Why Do Snakes Change Color?

Different habitats at different ages

The Green Tree Python (Morelia viridis) is a species surrounded by a unique mystery: the individuals undergo spectacular color change.

When hatching, the snakes are either bright yellow or red, and turn into a glossy green as the snake passes into adulthood. The species inhabits Cape York Peninsula (northeastern Australia), New Guinea and various islets and reaches 2 m (6 feet) length.

Dr David Wilson and Dr Robert Heinsohn from the Centre for Resource and Environmental Studies at Australian National University, with Professor John Endler of Exeter University solved the enigma of the species after a three year of study at Cape York Peninsula. "Animals sometimes change color during their lives, but none as dramatically as the green python of northern Australia and New Guinea. It has puzzled evolutionary biologists for decades," said Heinsohn.

"This beautiful reptile is popular in the pet trade because it hatches either bright yellow or red, but eventually turns emerald green. It turns out there is a very good reason for this dramatic change."

The team radio-tracked a large number of juvenile and adult individuals and investigated their colors using ultimate spectrophotometry. They discovered that the brightly colored youngsters live in a completely different habitat than the older snakes. The juveniles lived hunted outside the rainforest some small prey like skink lizards and cockroaches, whereas the adult snakes inhabit only the rainforest canopy, looking for rodents and birds.

The yellow and red color of the young help them camouflage within the multi-colored leaves and grass at the edge of the forest. Inside the dense foliage of the trees, the green of the adults is, of course, better suited for hiding from predators while hunting. "It was only when we established the total divergence in behavior of the juveniles and adults that we could begin to understand their remarkably different colors."

"It takes a year before the young ones are large enough to catch bigger prey like birds. They then shed their skins, change to green, and move inside the rainforest to try their luck off the ground."

"Drab juveniles are the norm in the animal world, but the brightly colored young of green pythons are unique. They are helping us to understand where the bright and beautiful colors seen in nature come from and how they are maintained," said Heinsohn.

Photo credit: Australian National University

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