There are many unsolved puzzles concerning the Taipei tree frog.

First, most frogs of northern Taiwan mate and reproduce in the spring and summer, and by autumn they are getting ready to hibernate. But the Taipei tree frog's mating season is in winter, and it is only during the winter that you will hear its distinctive croak.

Because of their topsy-turvy life cycle, they have fooled quite a few biology experts. Professor Lu Kuang-yang, for example. One nippy winter day, Dr. Lu pricked up his ears at an unusual animal call. He looked diligently in the chilly wind for a long time before discovering that the sound came from the Taipei tree frog, formerly believed to hibernate in the winter. Even stranger is that once the warm spring winds begin to blow, you are not likely to find a single one of the critters around.

It is not known just how they have adapted themselves to the cold weather, but some believe the frogs to be descendants of temperate-zone amphibians. Dr. Lu theorizes that they chose this seasonal niche because competitors and natural enemies are fewer in the winter, making it easier to find food.

Even more interesting about the Taipei tree frog is its habit of digging a hole for its nest. Though a wide range of animals, from wild mountain boars to pangolins, build nests for themselves, the Taipei tree frog is the only frog known to do so.

Rainy, humid weather is required for frogs to lay their eggs. Because winter is southern Taiwan's dry season, the Taipei tree frog is found only in mountainous areas under 1,000 meters in altitude north of Nantou County.

Their mating season is from October to April. First, the male burrows in some straw or dead grass to build a nest. He kicks up some dirt with his hind legs, then pats it into a little circular dam with his fore feet. He smooths out the bottom by rubbing it with his belly. This 7 cm or so nest provides a secure place for mating, egg laying, and for the young tadpoles after they hatch. Some less ambitious males may poach in a ready-made rat hole, redecorating to their own taste. A well-built nest is one of the things a female frog looks for in choosing her mate. Other influencing factors are low pitch and high volume in the male's croak.

The male begins his throaty recital after completing his nest. Hundreds of males singing together form quite a raucous chorus. A careful listener will notice that they perform in turns, each trying to outdo his predecessor.

Each male may mate up to six times in one season, and is "polygamous." However, in any one mating time, as many as four males have been observed to mate with one female.

Before laying her eggs, the female secretes a sticky substance from her posterior which she beats into a froth with her fore feet. This is the egg mass. Its outer surface hardens after coming in contact with the air; this seals the moisture inside. Ten days later, tiny tadpoles appear. After the next downpour, the tadpoles swim with the current to a puddle or pond to begin the next phase of their life. By approximately 40 to 60 days later, the tadpoles have fully developed fore and hind legs, are green in color, and their tail has shrunk. They measure about three or four centimeters, and can now live on dry land. Though they are called "tree frogs," they spend most of their time in the grass.

If caught, tree frogs play dead in self-defense. However, when undergoing body measurement and banding by a biologist, they seem to know that they have no way out, and cooperate submissively. Another protective feature of the tree frog is skin that can change color to blend into the environment, like a chameleon. It can go from green to yellow-green to inky green to deep purple to tan. And each change requires less than thirty minutes. Exactly how their color-changing mechanism works is not yet completely understood. It is thought that it involves glandular secretions in the frog's skin. This is but another of the many unsolved mysteries of the inscrutable--and fascinating--tree frog.

[Picture Caption]

(Below)A male frog that has just finished digging his hole tries it out for size. (Above Right) Hole completed, he croaks to attract a mate.(Below Right)In mating, a female beats her secretions into foam.

The Taipei tree frog changes color according to its location. (photo cou rtesy of Ch'en Shih-huang)

Hole completed, he croaks to attract a mate.（Below Right）In mating,.

a female beats her secretions into foam.

The Taipei tree frog changes color according to its location. （photo cou rtesy of Ch'en Shih-huang）