ASIAN TREEFROGS: Rhacophoridae

PHYSICAL CHARACTERISTICS

Asian treefrogs come in many sizes and colors, but they have a few common features. Almost all have sticky pads on the tips of their front and rear toes, which help them to move through trees and on leaves, even when they have to climb straight up. Most Asian treefrogs also have heads that are attached to the body with a noticeable neck. In many other frogs, the head blends back into the body without an obvious neck. The typical Asian treefrog has large eyes with horizontal pupils. Some members of this family have full webbing between all of their toes. In these frogs, which are known as flying or gliding frogs, the webs reach all the way to their toe tips. When their toes are spread wide, the feet almost look like fans. In a few species, including Wallace's flying frog, the frog also has a flat body and flaps of skin or fringe down the sides of the legs. These features give the frog's body a shape rather like that of a kite.

Asian treefrogs may be colored green, brown, gray, black, or white, often with markings on their backs. The underside may be a lighter version of the back color, or it may look completely different. Buerger's frog, for instance, is brown to gray on its back, but white on its belly. The Betsileo golden frog has a gray to brown back, but its underside is black. Most Asian treefrogs can hide well against their surroundings. Perhaps the species with the best camouflage is the Vietnamese mossy frog, which not only has a back and head that are the same green and brown as the moss on the ground, but also has spines and tall bumps, or tubercles (TOO-ber-kulz) that stand up just like the stems and leaves of the moss do. When this frog sits still on moss-covered rocks near streams or at the entrance of caves, a person could walk right past without ever seeing it.

The mantellas look different than most other members of this family. They do not have the toe pads that are common to other species, and they are very brightly colored. Some have red, orange, or yellow backs, while others have black backs and bright-colored legs. The painted mantella is an example. This frog has a black body, a white stripe on its head, legs that are orange on top and yellow underneath, and yellow shoulders.

Depending on the species, Asian treefrogs may be as small as 0.6 inches (1.5 centimeters) long from the tip of the snout to the end of the rump, or as much as 4.9 inches (12 centimeters) in length. The female is a bit longer than the male in many species, but in others, they are about the same size.

GEOGRAPHIC RANGE

Asian treefrogs live in southeastern Asia, the southern half of Africa, and Madagascar. In southeastern Asia, species live in southern India, Sri Lanka, central and southern China, Japan, Taiwan, the Philippines, Vietnam, Cambodia, and Indonesia. In Africa, they live in a stretch of land across the center of the continent from about the Ivory Coast in the west to Somalia in the east, and then down the eastern side.

HABITAT

Some species in this family live in forests. These include such frogs as Buerger's frog, the forest bright-eyed frog, Eiffinger's Asian treefrog, and the Luzon bubble-nest frog. Others, like the gray treefrog, prefer very dry grasslands. This gray treefrog, which is also known as the foam nest frog, is different from the eastern gray treefrog and Cope's gray treefrog of North America. Both of the North American species are members of a separate family, called the Amero-Australian treefrogs.

Some species in this family live near the water and use it to breed. They also use the water to lay their eggs. Buerger's frog is an example. The adults live in forests near rocky streams and enter the water to mate and lay their eggs. The eggs hatch into tadpoles, which remain in the water until they turn into froglets. Other species, like the free Madagascar frog, mate on the leaves of branches that overhang swamps or other water, and the female lays her eggs there on the leaves. As they hatch, the tadpoles plop down into the water, where they continue growing. Some Asian treefrogs live close to people. The golden treefrog, also sometimes called the banana frog, is often seen on the sides of trees in city parks and on bathroom walls.

DIET

Scientists know little about the diet of many species in this family. In those frogs that they have studied, the adult frogs eat ants, fruit flies, tiny spiders, and other small invertebrates (in-VER-teh-brehts), which are animals without backbones. They suspect that the other Asian treefrogs have a similar diet. Their tadpoles, however, are mostly vegetarian. They nibble at bits of algae (AL-jee) and dead plants that are stuck to and lying on underwater rocks or the water bottom. The tadpoles of two species, the Burmese bubble-nest frog and Eiffinger's Asian treefrog, also eat the eggs of other frogs.

BEHAVIOR AND REPRODUCTION

The Asian treefrogs are perhaps best known for three reasons: Some can glide through the air; some are poisonous; and some build foam nests. Although they are often called flying frogs, they can actually only glide. In other words, they cannot flap their legs to go higher in the air as a bird can with its wings, but they are able to soar from tree to tree. They do this by stretching out the webbing between their toes into a fan shape and using these large web-fans to catch the air and prevent them from falling too quickly. To glide, the frog typically reaches out in a Superman-like pose, but with the legs slightly bent. They adjust the angle of their feet to change direction in flight. Wallace's flying frog is an excellent glider. When this frog leaps from a height of 17.7 feet (7.3 meters), it can soar through the air for a distance of up to 24 feet (7.3 meters). Other gliding frogs include such species as the jade treefrog and the Himalaya flying frog. Besides being a quick way to get around the forest, gliding helps the frogs escape predators that cannot soar or fly.

The poisonous members of this family are called mantellas. Like the poison frogs of South and Central America, they have poison in their skin. Most of the other members of this family are active at night, which helps hide them from would-be predators. The mantellas, on the other hand, are not only active in the daytime, but they also sit right out in the open. Their bright colors draw even more attention to them. The golden mantella, for example, is bright yellow to orange, while the Betsileo golden frog is gold or orange gold with black sides. Scientists think the bright colors warn predators to leave the frogs alone. The poison in the mantellas is like that found in many of the poison frogs of South and Central America, but it is not as strong. It is, however, powerful enough to convince predators to pass by the frogs and look for something else to eat.

Some of the Asian treefrogs build foam nests. The gray treefrog is an example. First, a pair of frogs finds a spot in a tree branch that hangs over the water. Next, the female oozes a fluid before she lays her eggs, and she alone, or she and her mate, kick the fluid with their hind legs to whip it into foam. Once they have made a large amount of foam, she lays her eggs inside. The outside of the foam nest dries and hardens, but the inside stays moist. The eggs soon hatch into tadpoles inside the nest. By this time, the nest's bottom has become soft, often dissolving in a rain storm, and the tadpoles drop out of the bottom to the water below.

Except for the mantellas, mating in Asian treefrogs is mainly a nighttime activity. The males call to keep other males away and to attract females. The male common treefrog has a call that sounds like a deep quack; the male golden mantella makes quick, clicking noises; and males of other species have their own calls. In most species, the males call from or near a hidden spot or from a place where predators cannot easily reach. The male Buerger's frog calls from rocks in fast-moving streams, for instance, and the male Eiffinger's Asian treefrog does his calling next to the tree hole where he will mate. The mantellas, however, are very bold. These brightly colored males call loudly from open places in plain sight. Their colors serve them well at this time of year. They not only continue to warn predators of their poisonous skin and usually keep the frog safe, but they also tell other male frogs that an area is already taken. Sometimes two males fight over a good calling site. One will grab the other around the head and upper legs and try to push it away. This same type of fighting sometimes happens with female mantellas, but it is less common.

During mating, males typically climb onto the female's back and slowly squirt a fluid, which contains microscopic cells called sperm, onto the eggs while the female lays them. In the foam-nesting species, the male adds his fluid to the foam. In the gray treefrog, more than one male may add fluid. The eggs all have the same mother, but the father is whichever male added the sperm to the egg. In this way, the eggs in one nest may have several fathers.

In those species of Asian treefrogs that do not make foam nests, only one male mates with each female, and her young all have the same father. Sometimes, however, one male may mate with more than one female, and therefore be the father to several clutches of eggs. Depending on the species, the frogs may lay their eggs in foam nests, as described above, in tree holes, on the ground, or in still water. The painted Indonesian treefrog is one of the species that uses tree holes. A male and a female mate inside the tree hole over a puddle of water inside. The eggs stick to the inside wall of the tree. When they hatch, the tadpoles fall out of the eggs and into the water below. The Luzon bubble-nest frog is one of many species in which the female lays her eggs on the ground. In these species, the female usually lays only one dozen to three dozen eggs at a time. The Luzon bubble-nest frog, for instance, lays between five and nineteen large eggs. Like many other ground layers, she actually lays her eggs on the base of a leaf. Her eggs develop right into froglets there on the leaf, never becoming tadpoles in between.

Although the male golden mantellas usually do their calling from spots where they can be seen, male and female pairs mate in secret. Once a female approaches a calling male, the two find a hiding spot under a piece of bark or a rock that is next to some water. The eggs hatch into tadpoles, which then wriggle over the ground a short way until they plop into the water. The arboreal mantella, which is also sometimes known as the Folohy golden frog, mates differently. In this species, the female lays only one egg, which she sticks on an object above a puddle of water. Often, this puddle is inside a broken, standing piece of bamboo. The arboreal mantella is one of the only frogs in the world that lays one egg at a time.

Other frogs in this family breed in water. These include Buerger's frog and the forest bright-eyed frog, which both mate and lay their eggs in streams. The eggs hatch into tadpoles that continue growing in the water and eventually change into froglets.

Most of the frogs in this family breed over many weeks each year, but a few species mate during a very short period of only a few days. After they mate and lay their eggs, the males and females of many species leave their young to develop on their own. In a few species that do not lay their eggs in the water or in foam nests, the males will sit atop the clump of eggs while they develop. This may help to keep them moist or may help protect them from predators that might otherwise eat them. Some females of the foam-nesting species also stay nearby, sometimes returning to the nest to add more foam if necessary. They may even urinate on the nest to keep it moist enough for the eggs to survive.

The female Eiffinger's Asian treefrog lays her eggs on the inside of a tree hole and cares for her young. Instead of protecting them from predators or making sure they are moist, she feeds them. The water in the tree hole sometimes has little to feed the growing tadpoles, so she lays extra eggs in the water for her tadpoles to eat. Since these extra "blank" eggs have never mixed with sperm from a male, they would never have developed into young frogs, even if the tadpoles did not eat them. Arboreal mantellas do something similar. The female will drop a "blank" egg into the water for her tadpole to eat. Sometimes, however, the male becomes involved and leads another female to the water where one of his tadpoles is developing. If she lays her egg there, it may hatch into a tadpole that will become food for its older sibling.

The tadpoles of the common treefrog get no extra food from their parents. When they drop from their foam nests into the water, these hungry youngsters use their sharp and powerful beaks to eat almost anything in sight. If the water is just a small puddle, they may even eat their nest mates. Sometimes, only one tadpole is left in the puddle by the time it changes into a froglet.

JUST HOW MANY?

The number of species in the Asian treefrog family is uncertain. Some people separate out a group of the frogs into a separate family, called Mantellidae, but even when they are included, the overall number of species may differ by nearly one hundred. For example, the World Conservation Union (IUCN), which keeps track of risks facing different species, has a different total number than AmphibiaWeb, which is an online system offered through the University of California at Berkeley. The IUCN lists 156 species in the Mantellidae family and another 262 Asian treefrogs for a total of 418 species. AmphibiaWeb, on the other hand, counts 150 species in Mantellidae and 224 Asian treefrogs, which adds up to 374 species.

Depending on the species, tadpoles take different amounts of time before they change into froglets. The western white-lipped treefrog usually needs one or two months. Golden mantellas also take one-and-a-half to two months, but other mantella species may need a longer time to change into froglets.

ASIAN TREEFROGS AND PEOPLE

People rarely see most of the species in this family, which live in forests and other areas away from human activity. Some of the Asian treefrogs, like the Kinugasa flying frog, often turn up in gardens where people notice them. A few species, including the beautifully colored mantellas, are popular in the pet trade.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists eighteen species that are Extinct, which means that they are no longer in existence; twenty-five species that are Critically Endangered and face an extremely high risk of extinction in the wild; fifty-six species that are Endangered and face a very high risk of extinction in the wild; forty-nine that are Vulnerable and face a high risk of extinction in the wild; thirty-eight that are Near Threatened and at risk of becoming threatened with extinction in the future; and ninety-four that are Data Deficient, which means that scientists do not have enough information to make a judgment about the threat of extinction.

The eighteen Extinct species have not been seen in the wild for at least fifty years, and some of them for more than one hundred years, even though scientists have searched for many of them again and again. One of the Critically Endangered species is the Chalazodes bubble-nest frog. Scientists had thought this species was extinct for 125 years when a population was discovered in a small area of moist forest on a hillside in India. It is still in danger, however, because it only appears to live in this one spot, and the forests are disappearing as people turn them into farms.

The Shillong bubble-nest frog, which is also Critically Endangered, lives in a different small area of India. The frog was quite common in its forest as late as the 1970s, but it has now become so rare that scientists have not even been able to hear a single male calling during the frog's breeding season. Like the Chalazodes bubble-nest frog, the Shillong bubble-nest frog's forests are disappearing as people cut the trees for lumber or firewood or to make room for houses and buildings. Another of the Critically Endangered species, known only by its scientific name of Philautus papillosus, is also facing habitat loss, but this time it is mainly due to mining for gemstones. Miners cut down trees that are in the way of their work. The endangered Romer's treefrog, which lives in Hong Kong, has lost some of its habitat as people move into its forests and marshes but has also been pushed out by the building of a new airport. Ecologists tried to protect the frog by moving some populations. As of 2004, they had moved the frogs to eight new locations in protected areas, and seven of these populations were doing well.

KINUGASA FLYING FROG (Rhacophorus arboreus): SPECIES ACCOUNTS

Physical characteristics: Also known as the forest green treefrog or the Japanese treefrog, the Kinugasa flying frog may be a solid, limegreen color, dark green, or green with many reddish brown, brown, or black speckles. The reddish brown and brown speckles are outlined with black. The frog's back, head, and legs are rough and covered with small bumps, or tubercles. Whether solid or speckled, its underside is white or cream-colored, often with somewhat-faded, brown blotches on the chest and throat. They have two large eyes bulging from the sides of a rather flattened, but large head. The eyes, which are orange to brown, often have a noticeable dark band running between them. They also have a noticeable ridge on each side of the head, stretching from the end of the snout to the middle of the eye and continuing on the other side of the eye where it curves down toward the top of the shoulder. The snout narrows toward the front. The legs are slender, and the underside of the rear legs has black lines and blotches near the body. The front toes are slightly webbed, but the hind toes are fully webbed. The toes on all four feet are long and have very large, triangular-shaped pads on the tips. Females are larger than males. Females reach 2.3 to 3.2 inches (5.9 to 8.2 centimeters) from the tip of the snout to the end of the rump, while males grow to 1.7 to 2.4 inches (4.2 to 6.0 centimeters) in length.

Geographic range: Its home is in Honshu, the largest of the islands that make up Japan, as well as on a small island, called Sado, just to the northeast of Honshu. In addition, it has been introduced to two other areas in Japan.

Habitat: Although they can live in lowland forests, Kinugasa flying frogs usually prefer wooded locations high in the mountains, sometimes more than 6,560 feet (2,000 meters) above sea level. Tadpoles develop in the water of rice fields, marshes, and other wetland ponds.

Diet: Its diet is made up of insects.

Behavior and reproduction: Usually found in mountains, the Kinugasa flying frog sits among trees or under piles of leaves along the ground for much of the year. It sometimes also enters people's gardens and makes its home there. In the cold winters of this area of Japan, the frog finds a spot under a layer of moss or buried just under the ground and enters a state of deep sleep, called hibernation (high-bur-NAY-shun), until the weather warms again the following spring. The breeding season for this frog is about four months long, from April to July. The breeding season begins when males hop to the edge of a pool or wet rice field and start calling. Each male makes a similar call, which is two to six clicking noises followed by several lower clucks. After a female follows a call to a male, he climbs on her back, and she releases a fluid rather like the raw egg white from a chicken's egg. She then kicks the fluid with her feet, beating it into a foam. Sometimes the male helps her in whipping up the fluid. The longer the foam is beaten, the larger it grows. When it reaches an oblong shape about 3.5 inches (8.8 centimeters) wide and 4.7 inches (12.0 centimeters) long, she lays her eggs inside the frothy nest. As she does, the male adds his own fluid, which is filled with microscopic cells, called sperm. When the sperm combine with the eggs, the eggs can start to develop into young frogs. A female may lay three hundred to eight hundred eggs in the nest.

Sometimes, the mating pair is not alone. Other males may join in by beating up the foam and by adding their own sperm-filled fluid to the nest. In this way, the eggs in one nest may not all get sperm from the same male. When this happens, the young frogs from one nest may have different fathers. Once all the eggs are laid, the outside of the nest starts to dry into a hard shell. The shell protects the eggs from other animals that might want to eat them, and it also keeps the foam inside from drying out. The eggs eventually hatch into tadpoles inside the nest. By this time, the bottom of the nest becomes soft, and the tadpoles fall out, dropping into the water below. There, they continue their growth and turn into froglets.

Kinugasa flying frogs and people: In some ponds in Japan, the frogs have become a tourist attraction. Here, hundreds of male and female frogs arrive together to mate at night and during the day, and people come from miles away to watch this natural scene. Away from these busy ponds, people who live in the countryside also enjoy hearing smaller groups of males calling from rice fields and pools of water on summer nights.

Conservation status: This frog is quite common, and the IUCN lists it as being of Least Concern, which means it has no known threat of extinction and does not qualify for any of the "threatened" categories. It lives in numerous protected areas, and because some populations are tourist attractions, people keep a careful watch over them. ∎

PAINTED INDONESIAN TREEFROG (Nyctixalus pictus): SPECIES ACCOUNTS

Physical characteristics: The painted Indonesian treefrog, also known as Peter's treefrog or the cinnamon treefrog, may be bright orange, red, orange brown, or brown in color and looks as if it has been painted with tiny white dots. This dotted pattern gives the frog another of its common names, the spotted treefrog. Sometimes the dots form a broken line from the snout over the eye and to the back. The frog has a rough back with small and pointy bumps on its upper surface. On its underside, the frog is a paler orange or orange brown color. The head is flat like the body and narrows to a dull point at the end of its fairly long snout. It has two very large eyes, one on each side of the head. The eyes are white on top and brown on the bottom.

This species is a slender frog with very long and thin hind legs that fold neatly against its flattened body when it is sitting still. Its front legs are also quite thin, and the frog likewise holds them tucked close to its body. On the front feet, the toes may be unwebbed or may have a small amount of webbing between them. The toes of the rear feet have more webbing. Females are larger than males. Females reach 1.46 to 1.54 inches (3.7 to 3.9 centimeters) from the tip of the snout to the end of the rump, while males grow to 1.12 to 1.5 inches (3.0 to 3.7 centimeters) long.

Geographic range: It lives in southeastern Asia, including Sumatra and Borneo in Indonesia, Palawan Island of the Philippines, Malaya, Sumatra, Singapore, and the southern edge of Taiwan.

Habitat: Adults live in moist forests either in lowlands or high in mountains up to 5,400 feet (1,650 meters) above sea level. For the frogs to survive, the forests must not be disturbed by humans. Tadpoles develop in puddles of water inside tree holes.

Diet: Although they do not know for sure, scientists believe they probably eat the same types of food as other members of this family: small invertebrates.

Behavior and reproduction: Scientists know little about this frog's behavior. Some adult frogs have been spotted from 3.3 to 9.8 feet (1 to 3 meters) above the ground on the leaves of small trees and shrubs, but they may climb even higher in the trees. The frogs breed in tree holes and rotting logs that contain puddles of water from the rain. Females lay about ten eggs at a time in a clump of gel that sticks to the inside wall of the tree hole or hollow log just above the puddle. The eggs hatch into tadpoles, which drop down into the water. They are able to survive by eating little bits of dead leaves or other material that is in the puddle. The tadpoles grow inside the puddle and eventually turn into froglets.

Painted Indonesian treefrogs and people: This frog does not survive well in forests that have been changed by people. Even a small amount of logging can cause a population to die off.

Conservation status: The IUCN considers this species to be Near Threatened, which means that it is at risk of becoming threatened with extinction in the future. Although the frogs live in many areas of southeastern Asia, they are not common anywhere. Ecologists are concerned about the future of this frog because more and more of its forests are being cut down by local people and by loggers. Some populations of the painted Indonesian treefrog live in areas that are protected from logging. ∎

FREE MADAGASCAR FROG (Mantidactylus liber): SPECIES ACCOUNTS

Physical characteristics: This is a slim frog with slender front and rear legs and extremely thin toes. Its front legs, including the long toes, would be about as long as the frog's body if they were stretched out. The toes on all four feet end in large pads. The front toes have no webbing between them; the back toes are slightly webbed. The frog's back, head, and legs are red, gray, or green, often smeared with patches of a slightly different second color. For example, a frog may have a pinkish brown back colored with light brown or greenish brown patches. A faint light line runs from the snout over the head and down the back. Some white or yellow spots may be noticeable low on the sides, especially toward the rump, and a few white speckles may show on the sides of the head and neck. The underside of the frog may be black. Its head has a rather long snout that narrows toward the front, and one eye of the large, gold to copper-colored pair of eyes on either side. A dark bar may show between the eyes. A narrow ridge runs from the back of the head to the shoulder.

Males have a flat structure, called a gland, under the skin on the upper rear leg, and a large, white vocal sac in the throat region. The vocal sac, which is also seen in other species of Asian treefrogs and many other types of frogs, blows up like a balloon when the male makes his call. Males are often a bit smaller than females, but both can grow to the same size. Males reach 0.8 to 1.1 inches (2.1 to 2.9 centimeters) from the tip of the snout to the end of the rump, while females grow to 1.06 to 1.1 inches (2.7 to 2.8 centimeters) long.

Geographic range: They live on the eastern side of Madagascar, as well as in the central region of the country.

Habitat: They live in moist rainforests from lowland areas at sea level to mountain locations up to 3,900 feet (1,200 meters) above sea level. Tadpoles develop in shallow water of swamps and other wetlands.

Diet: The diet is probably like that of many other treefrogs: small arthropods, including insects and spiders.

Behavior and reproduction: Most of the time, this frog sits in or near plants with cup- or tube-shaped parts that fill with water. The rainiest time of year is the mating season for the free Madagascar frog, and males begin calling from plants around the still or slow-moving water of small pools and swamps. The male's call is a ticking sound. When a female answers his call, she approaches him and may even give him a little push from behind. He then climbs onto her back and begins to wiggle. As he does, she lays her eggs onto the leaves. Each female may lay thirty to ninety eggs. When the eggs hatch into tadpoles, the tadpoles drop off the leaves and plop into the water below. They stay in the water until they develop into froglets.

Free Madagascar frogs and people: This frog survives quite well in rainforests that humans have not disturbed and in rainforests that have seen a good deal of human activity, such as the cutting of some trees for farming or other purposes.

Conservation status: This frog is quite common, and the IUCN lists it as being of Least Concern, which means it has no known threat of extinction and does not qualify for any of the "threatened" categories. Scientists are, however, watching this and other frog species as the rainforest disappears. Fortunately, the free Madagascar frog lives in many places that are protected from habitat destruction. ∎

FOR MORE INFORMATION

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Channing, A. Amphibians of Central and Southern Africa. Ithaca, NY: Comstock Publishing Associates, 2001.

Glaw, F., and M. Vences. A Fieldguide to the Amphibians and Reptiles of Madagascar. Frankfurt, Germany: Edition Chimaira, 1999.

Halliday, Tim, and Kraig Adler, eds. The Encyclopedia of Reptiles and Amphibians (Smithsonian Handbooks). New York: Facts on File, 1991.

Inger, R. F., and R. B. Stuebing. A Field Guide to the Frogs of Borneo. Kota, Indonesia: Natural History Publications, 1997.

Maeda, N., and M. Matsui. Frogs and Toads of Japan. Tokyo, Japan: Bun-Ichi Sogo Shuppan Co., 1990.

Mattison, Chris. Frogs and Toads of the World. New York, NY: Facts on File Publications, 1987, pp. 177–179.

Miller, Sara Swan. Frogs and Toads: The Leggy Leapers. New York: Franklin Watts, 2000.

Passmore, N. I., and V. C. Carruthers. South African Frogs: A Complete Guide. Johannesburg, South Africa: Witwatersrand University Press, 1995.

Showler, Dave. Frogs and Toads: A Golden Guide. New York: St. Martin's Press, 2004.

Schiøtz, A. Treefrogs of Africa. Frankfurt, Germany: Edition Chimaira, 1999.

Zug, G. R., L. J. Vitt, and J. P. Caldwell. Herpetology: An Introductory Biology of Amphibians and Reptiles. San Diego, CA: Academic Press, 2001.

Periodicals:

Milius, Susan. "Lifestyles of the Bright and Toxic Overlap." Science News (April 14, 2001): 230.

Williams, Wendy. "Flash and Thunder." Animals (July 2000): 25.

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