AFRICAN TREEFROGS: Hyperoliidae

PHYSICAL CHARACTERISTICS

African treefrogs are also known as reed and sedge frogs. The typical African treefrog has a slender body, large and often bulging eyes usually with horizontal pupils, and rounded pads on the ends of its webbed toes. Its back legs are long and thin, and its front legs are also quite thin. The treefrogs with this appearance are good climbers and leapers. Some of the African treefrogs look quite different. These species, which are often called running frogs, remain on the ground; have no toe pads or toe webbing; have shorter hind legs, frequently only a bit longer than the front pair; and walk or run rather than hop.

The males of this family have large vocal sacs, which are pouches in the throat area that blow up and then deflate when they call. Male African treefrogs have a vocal sac, which may blow up to be three or more times as big as the head. In many species, this sac is covered with an oval-shaped flap that can be seen even when the frog is not calling.

The African treefrogs come in many different colors and patterns. In some cases, even members of the same species do not look alike. One member of the species known as the painted reed frog, for example, may be green with a few dozen, tiny, black-centered, yellow spots on its back, orange toes, and orange upper legs. Another might be greenish gray with large black blotches, tan with black and yellow markings on its sides, or cream with black and orange stripes. The following examples will show the varying colors among different species within this family:

• Greater leaf-folding frog, also known as the spiny leaf-folding frog—Chocolate brown with a wide silvery to light brown back, which is sometimes split down the middle with a chocolate brown stripe; also with silvery to light brown color on the top of the hind legs
• Yellow-striped reed frog—Light green with a yellow stripe on each side of its body from the snout over the large, orange-colored eye to the rump; orange toes and a yellow underside with orange on its rear legs
• Yellow-legged kassina, also known as the yellow-legged treefrog—Beige with many brown spots on its back, brown bands on its legs and toes, and yellow on the underside of upper rear leg
• White-spotted reed frog—White, covered with small yellow dots that are outlined in dark brown
• Transparent reed frog, also known as the water lily reed frog— Light green with orange toes
• Malagasy variable reed frog—Orange yellow with small brown spots on the head and front half of the back and a narrow brown stripe on each side of the snout
• Madagascar reed frog, also known as the blue-back frog—Baby blue head and back, orange yellow underside, dark orange toes, two black stripes from the snout to the eyes, and a few black spots on both sides between the eye and the front leg and on the front leg

Depending on the species, African treefrogs may have eyes that are all brown, gold, whitish, or some other solid color, or that are one color on the top half and another on the bottom half. The Malagasy variable reed frog, for instance, has large eyes that are white on the bottom and pinkish on the top. Most of the treefrogs have large eyes, but in some species they are enormous. The Seychelles treefrog is an example. Its pearly white eyes look almost like big headlights.

Often the color of the frog changes as it grows older. Young froglets in many species are yellow or brown with dark markings down the back, while the adults are brightly colored and patterned. In some species, the youngsters are green, while the adults are brownish. Scientists call these colors the "juvenile phase." Sometimes, many of the adult males have the juvenile colors during the breeding season, too.

Adult African treefrogs may be as small as 0.5 inches (1.2 centimeters) long from the tip of the snout to the end of the rump or as large as 4.3 inches (11.0 centimeters) in length. While males and females are the same size in many species, the females are larger in others. The African wart frog and the greater leaf-folding frog are two species in which the males and females reach the same size. Adult African wart frogs grow to 1.4 inches (3.6 centimeters) long, and adult greater leaf-folding frogs reach 1.6 inches (4.1 centimeters) in length. Female toad-like treefrogs, on the other hand, are larger than males. In this species, females grow to 1.4 to 1.6 inches (3.6 to 4.1 centimeters), while males reach only 1.1 to 1.3 inches (2.9 to 3.3 centimeters) in length. The difference between the sexes is even more noticeable in the big-eared forest treefrogs. Here, females reach up to 3.3 inches (8.4 centimeters) long, while males are about half that size at 1.6 to 1.8 inches (4.1 to 4.6 centimeters) in length.

GEOGRAPHIC RANGE

African treefrogs live in most of central and southern Africa. Some species are also found on the large island of Madagascar and the tiny island of Seychelles, which are in the Indian Ocean east of southern Africa.

HABITAT

Many species in this family live in often dry and hot grassy fields or in areas that are humid and covered in thick bushes and trees. In addition, some live in rainforests, and others tend to make their homes in land that is currently being farmed or in abandoned and overgrown farmland. Some of the African treefrogs live high in mountains, but many others do not. Many species are arboreal (ar-BOR-ee-ul), which means that they live above the ground in trees. Other species stay on the ground, and some are able to dig beneath it.

DIET

They eat mainly invertebrates (in-VER-teh-brehts), which are animals without backbones. They especially eat insects and other arthropods (AR-throe-pawds), which are invertebrates with jointed legs, but they will often add any other animal they can capture and swallow. Usually treefrogs and other species of frogs only eat things that are moving, but at least one of the African treefrogs will eat non-moving things. This treefrog, called the greater leaf-folding frog, will eat the eggs of other frogs that make foam nests for their young. The greater leaf-folding frog pokes its head through the nest and eats the eggs inside.

BEHAVIOR AND REPRODUCTION

African treefrogs are active at night, which is when they look for food and mate. During the day, some of the species that live in hot, open areas dig down into the soil where it is cooler and moister. Scientists are not sure, but they think that some of them, including the toad-like treefrog, either remain underground for the entire dry season in a state of deep sleep, known as estivation (es-tih-VAY-shun), or come out on humid mornings to search for food. Some of these burrowing species shed their skin when they are underground, and this skin dries into a sort of cocoon. The frog remains inside the cocoon, which helps to keep the frog moist. Other species of treefrogs are outdoor types and stay outside even on very hot and dry days. They are not active during the day, however, and simply sit still on leaves until the evenings arrive. The painted treefrog survives hot and dry days by oozing mucus from its skin. This mucus is waterproof, but instead of keeping moisture out, it keeps the moisture in. Even so, they often lose some water from their bodies. Some young painted treefrogs are able to survive even after their bodies have lost half their weight in water. The sharp-nosed reed frog protects itself from dry weather simply by staying down low in grasses on hot days. There, the air is more humid.

The typical African treefrog mates during the rainy season. Males head to the water, often a small pool formed by the rains, and begin calling. Sometimes, the males reach the mating area even before the rains have filled the pools. Not all species mate in new pools on the ground. The African wart frog and others mate inside a tree hole above a puddle of water. Scientists still do not know where some species, such as the toad-like treefrog, mate.

Using their often-enormous vocal sacs, the males make a variety of calls. The greater leaf-folding frog, for instance, calls with a creaking sound followed by several clicks in a row. The bubbling kassina makes a sound like tiny bubbles popping. The males of the Afrixalus brachycnemis and other similar species are unusual because their calls have two parts. In this species, the first part is a zipping sound, and the second is a trill. The zipping sound tells other males of the same species to stay away, and the trill is an invitation to females interested in mating. The males of a few species, including the African wart frog, may not be able to call at all.

For those species that mate at tree holes, only one male uses each tree hole, and the female follows his call to him. It is not so easy for those that mate in ground pools. There, many males of several different species of African treefrogs may use the same pool for mating and call at the same time. Despite the confusion of calls and the large number of frogs, a female can pick out the call of a male from her own species and follow that call to a mate. In some species, the female is stopped on her way to a calling male by another male that is not calling, and she mates with him instead. These quiet males that hang around a calling male waiting for a chance to meet a female are called satellite (SAT-eh-lite) males.

The majority of the species in this family lay their eggs on leaves that hang over pools of water on the ground. For example, the female Betsileo reed frog of Madagascar lays her sticky eggs on leaves just above the water. These eggs hatch into tadpoles, and the tadpoles use their tails to wriggle off the leaves and fall into the water. The leaf-folding frogs also lay their eggs on grass blades or other leaves above a pool of water, but then fold the leaf around the eggs. Since the gel-covered eggs are sticky, the leaf stays folded. When the eggs hatch into tadpoles, the tadpoles wriggle off the leaf and into the water below. In at least one species of leaf-folding frogs, known as the delicate spiny reed frog, the female may mate with more than one male in a night, so the young in her batch of eggs may have different fathers.

The gray-eyed frog is the only species of African treefrog in which the parents provide a foamy nest inside the folded leaf for their eggs. The female makes mucus and then beats it with her hind legs until it turns into foam. She lays her eggs in the foam, and the male folds the leaf around them. The foam helps keep the eggs moist. The eggs hatch, and the tadpoles fall off the leaf and into the water below. Some species of treefrogs, including the kassinas and the sharp-nosed reed frog, lay their eggs right in pools of water along the ground. They typically stick their eggs, sometimes one at a time, onto underwater plants.

Several species, such as the African wart frog, mate in tree holes that hold water. The female lays her eggs on the inside wall of the hole just above the water. The eggs are coated in a gel and stick to the wall. When they hatch into tadpoles, the tadpoles drop into the water. The big-eared forest treefrog and a few other species do not lay their eggs in the water. Instead, these frogs bury their eggs in moist soil that may be 33 feet (10 meters) or more away from any water. Their eggs are large and filled with yolk, which provides food for the young. Eventually, the tadpoles are strong enough to wriggle along the ground to the water, where they continue to grow. In at least one egg-burying species, known as the giant big-eyed treefrog, the eggs do not hatch into tadpoles at all but hatch right into froglets.

Depending on the species, the number of eggs that a female lays may be as few as a dozen or as many as two hundred or more. The female sharp-nosed reed frog and the Seychelles treefrog are two examples of African treefrogs that lay large numbers of eggs. A typical clutch for a sharp-nosed reed frog is about two hundred eggs, while that of the Seychelles treefrog may be as many as five hundred. In most species of African treefrogs, the adult females lay the eggs and leave them to develop on their own. The African treefrog species known as the midwife frogs are different. The females stay with the gel-covered eggs until they hatch and then help the tadpoles escape from the gel.

The tadpoles of many African treefrogs change into froglets within weeks. Some, like the African wart frog, may wait until they are about three months old before going through the change, which is known as metamorphosis (meh-tuh-MOR-foh-sis). They may need this much time to grow because they live in small pools of water inside tree holes, where food may be very scarce. The sharp-nosed reed frog, on the other hand, lays its eggs in larger pools on the ground. When the tadpoles hatch from the eggs, they find plenty of food and grow so quickly that they can turn into froglets and be ready to mate and have their own young before the end of the breeding season in which they were born.

NOW, THAT'S A SUPER SPECIES!

To some scientists, the painted reed frog should actually be divided into several species. This is because painted reed frogs from one area can look much different than painted reed frogs from another area and because frogs from these separate groups sometimes will not mate with one another even when they live together in the same place. For now, the painted reed frog is often called a super-species, which means that it is a group of two or more species instead of just one.

AFRICAN TREEFROGS AND PEOPLE

Some people keep African treefrogs as pets, but most people are happy to enjoy the frogs only by listening to them calling in the wilds of Africa.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists one species as Critically Endangered and facing an extremely high risk of extinction in the wild; nineteen species as Endangered and facing a very high risk of extinction in the wild; twenty-nine that are Vulnerable and facing a high risk of extinction in the wild; sixteen that are Near Threatened and at risk of becoming threatened with extinction in the future; and fifty-three that are Data Deficient, which means that scientists do not have enough information to make a judgment about the threat of extinction.

The one Critically Endangered species is known by its scientific name of Alexteroon jynx. It has only been found in two small areas on hillsides in southwestern Cameroon. This frog lives among thick plants along forest streams that are shaded by overhead trees. It lays a few eggs together in a group on leaves above the water. These eggs hatch into tadpoles, which slide off the leaf and into the stream. Ecologists are concerned not only because it lives in such a small area but also because the forests are not protected and are disappearing as people cut down the trees. Unless the area is protected soon, they fear that the frogs will become extinct.

The Knysna banana frog, Pickersgill's reed frog, and the long-toed treefrog are examples of the Endangered species in this family. All three live in South Africa. The Knysna banana frog is a rare species that lives along the southern coast of South Africa in shrubs, forests, and sometimes farmland; it mates among plants that grow in small pools of water and dams. Pickersgill's reed frog lives in shrubby areas and grasslands farther up the coast of South Africa and uses small pools of water that may dry up later in the year. The home of the long-toed treefrog is in inland grasslands, often on mountainsides between 3,280 to 6,000 feet (1,000 to 1,830 meters) above sea level. It mates in marshes and other grassy pools that may dry up later on.

Human activity, such as the construction of buildings, cutting of trees, and draining of water from wetlands for farms, is causing problems for all three species. In the case of the Pickersgill's reed frog, people are also using the insect-killing chemical known as DDT to control mosquitoes. These mosquitoes can bite people and spread a sometimes-fatal disease called malaria (muh-LAIR-ee-uh). DDT, however, can also kill frogs. Besides this threat, the frogs are in danger because people have brought in eucalyptus (yoo-cuh-LIP-tus), a new plant that can soak up much of the water in a wetland. Water-loving introduced plants, as well as fires, are causing a problem for the long-toed treefrogs. Although each of these species is endangered, some of them make their homes at least partially inside a protected area, such as a national park or nature reserve.

BUBBLING KASSINA (Kassina senegalensis): SPECIES ACCOUNTS

Physical characteristics: The bubbling kassina, also known as the Senegal running frog, is a light greenish gray to tan frog with wide, dark, often brown or black striping or spots on its head and back and dark blotches on its front and rear legs. In many, the markings on the back and head include one long stripe beginning between the eyes and continuing almost to the rump, one broken stripe on each side, a stripe from the tip of the snout to at least the shoulder, and another blotch or several spots low on each side. On its head, the large eyes may look light olive gray to tan or gold, and each has a vertical pupil. Most other African treefrogs have horizontal pupils. Its front legs are not overly long, and its hind legs are only a bit lengthier than the front pair. Both have a pattern of dark bars on lower legs and onto the feet. The front toes have no webs between them; the rear toes have a little webbing. Its belly is white.

Males and females are about the same size. They each reach about 1 to 1.9 inches (2.5 to 4.9 centimeters) long from the tip of the snout to the end of the rump. In some areas, the size of the frogs is on the small side, but in others, most grow closer to the maximum size of 1.9 inches (4.9 centimeters) in length.

Geographic range: It lives over the southern two-thirds of Africa from South Africa north to parts of Sudan, Mali, Ethiopia, Senegal, Niger, and Chad.

Habitat: These frogs are terrestrial (te-REH-stree-uhl), which means they live along the ground. For much of the year, they are usually found in grassy areas, although some make their homes in more shrubby areas, in pastures, or in country gardens. They mate in shallow spots in ponds or swamps, usually those places with a good deal of plants living in the water.

Diet: These frogs probably eat arthropods.

Behavior and reproduction: With its small hind legs, the bubbling kassina does not hop but instead walks or runs, which is why it is sometimes called the Senegal running frog or simply a running frog. When it sits still, this small striped frog almost disappears against the blades of grass in the grasslands where it lives. It becomes much more noticeable when the rainy season arrives and the males begin calling. The male's call is a high "poink" sound that is rather similar to a bubble bursting or a drop of water landing in a small, metal tub. The male only makes one "poink" sound at a time, usually waiting a while between the sounds. Males call at night while sitting in grass, often on the shore of a pond or swamp and under an overhang, such as a low, dirt cliff. They may also call from a spot in shallow water and surrounded by grass. Females join the males to mate with them in the water. A female lays her eggs one at a time on underwater plants. Each egg has a gel coating, and groups of them may stick together in a clump on the plants. The eggs hatch into tadpoles, which have wide fins, and pointy tails.

Bubbling kassinas and people: Many people in the grasslands of Africa enjoy the call of the bubbling kassina. Yet they very rarely actually see one. As a person nears a calling frog to find it, the frog stops calling and sits still. When the frog is not moving, its color and pattern help it to blend into the grass and make it very difficult to spot.

Conservation status: The IUCN lists this species in the category of "least concern," which means that it is under no known threat of extinction and the animal does not qualify for any of the Threatened categories. The bubbling kassina is a common species that lives over a large part of Africa, including numerous parks and other protected areas. ∎

PAINTED REED FROG (Hyperolius viridiflavus): SPECIES ACCOUNTS

Physical characteristics: Painted reed frogs, also known as common reed frogs, are hard to describe because they come in so many colors and patterns. Some of them are striped in black and yellow from head to rump and on their legs. Some are speckled in green and black on a cream background or have a black-and-white spotted back and brown sides. Others are tan to brown with wide yellow and black bands on their sides and dark gray toes with orange tips. They have many different common names based on what they look like and where they live.

Despite the differences in colors and patterns, all painted reed frogs share certain features. They all have slender bodies, no noticeable neck separating the short head from the body, two large eyes with one on either side of the head, and thin legs. Their pupils are horizontal, and no eardrum shows on the side of the head. Their snouts narrow toward the front and are rounded at the end. The front and hind feet have webbing between the toes, and the toes have rounded pads at the ends. Their bellies are usually white, but sometimes may be pink. Male painted reed frogs have one large, dark gray vocal sac on their throats that blows up and deflates like a balloon when they call. Sometimes the vocal sac has tiny orange spots. The females do not have this sac, but they do have a side-to-side fold across the throat. They typically grow to about 1.2 inches (3 centimeters) in length.

Geographic range: They live over most of the southern two-thirds of Africa.

Habitat: Many of the painted reed frogs live in grasslands, but one group found in central Africa and a small area in West Africa makes its home in forests. They mate and lay their eggs in ponds and sometimes in swamps and even slow-moving streams.

Diet: These frogs probably eat arthropods.

Behavior and reproduction: Unlike most frogs that hide during the daytime, some of the painted reed frogs sit out in the open. Often, the frogs that sit in plain view are those that are brightly colored. These colors may be a warning sign to the predators that the frogs are not good to eat because they have poisonous skin. Many of the painted reed frogs that live in dry, hot grasslands are able to rest in the sun without drying out and dying because they can make a thin layer of mucus to cover their bodies. This mucus hardens into a waterproof coat that keeps the frog's skin moist inside. Some, especially the younger frogs, are also able to survive even if their bodies lose up to half of their weight in water. In particularly dry weather, many of the frogs become white. Darker colors soak up more heat from the sun, so the white color helps to keep the frog a bit cooler.

Painted reed frogs mate during the rainy season. The males sing together in choruses (KOR-us-es) or groups, which sounds like the ringing of small bells and can make a lovely music in the African grasslands and forests. Males call from tall grass-type plants, called reeds and sedges, along the shores of ponds, but sometimes also call from taller bushes and trees. Females lay up to a dozen eggs underwater on plants. In captivity, the frogs will often mate and lay eggs every few weeks during the breeding season, but this behavior has not been seen in the wild. The eggs hatch into tadpoles that turn into froglets. The young froglets may be quite large, and they may be able to become parents themselves later that same year. At least one research team reported that a female painted reed frog may sometimes turn into a male.

Painted reed frogs and people: The frogs may have poisonous skin, and some people in Africa believe that a cow will die if it eats a frog.

Conservation status: In its listing, the IUCN has split up the painted reed frog into several different species, which include the "main" species Hyperolius viridiflavus, the marbled or painted reed frog with the scientific name Hyperolius marmoratus, Hyperolius marginatus, and several others. The IUCN lists these three to be of "least concern," which means that they are under no known threat of extinction and the animals do not qualify for any of the Threatened categories. According to the IUCN, all three are very common, and one (the marbled reed frog) is even spreading into new areas, especially any new water pools that people make. These three frogs also make their homes inside various protected areas, which should limit the clearing of land where they live. ∎

AFRICAN WART FROG (Acanthixalus spinosus): SPECIES ACCOUNTS

Physical characteristics: The African wart frog is covered with warts on its head, back, and the tops of its legs. It is an olive green, gray, or brown frog with dark bands—sometimes broken bands—that run from one side of its back to the other. It has thin legs, some webbing between the toes of its front and hind feet, and round pads on the tips of its toes. It has large brownish eyes and a rather long snout that narrows toward the front. This frog has an orange tongue. It can grow to 1.4 inches (3.6 centimeters) long from its snout to its rump. Young frogs are orange and maroon.

Geographic range: It lives in west-central Africa, including Cameroon and the Democratic Republic of the Congo.

Habitat: This frog makes its home in rainforests that are thick with trees and plants. It spends most of its time in water-filled holes of either living or dead trees, sometimes in holes of large branches.

Diet: Although scientists are not sure what they eat, they suspect that these frogs probably eat arthropods, as do many other species in this family.

Behavior and reproduction: The African wart frog is active at night. During the day, it typically sits in a puddle of water that has formed inside a tree hole or a pocket on a branch. Usually, the frog floats underwater with just its nostrils sticking out into the air. The frog may hop out of the water at night to find food. Its body colors and patterns help to hide it from predators, but if a predator does see the frog and comes too close, the African wart frog closes its eyes, tucks its legs in tight against its body, and thrusts out its tongue. This may startle a predator enough that it leaves the frog alone.

This frog mates near the water of its tree hole or branch. Unlike other frogs, the male African wart frog does not have a vocal sac and does not make a call, so a female cannot find him by hearing him. Instead, scientists think the male and female locate each other by smell. The pair mate above the water, and the female lays eight to ten yellow-colored eggs that attach with a sticky gel to the wall of the tree or branch hole barely above the water. The eggs hatch into tadpoles, and the tadpoles drop down into the water, where they live and grow for about three months. During that time, they eat little bits of food that they find in the water, such as pieces of plants. They then turn into froglets.

African wart frogs and people: People rarely see this frog. Since the males make no calls, people never hear them either.

Conservation status: The IUCN lists this species in the category of "least concern," which means that it is under no known threat of extinction and the animal does not qualify for any of the Threatened categories. With many species of frogs, scientists estimate the size of the population during the mating season when the males are calling and the frogs are easiest to find. Since the males in this species of frog are quiet, scientists have not been able to make good estimates about the frogs' numbers. Nonetheless, they believe the frogs are quite common. Since the frogs mate and lay their eggs in the holes of trees, the logging of these trees may cause a problem for the frogs in the future. ∎

FOR MORE INFORMATION

Books:

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

Lovett, Sarah. Extremely Weird Frogs. Santa Fe, NM: John Muir Publications, 1991.

Mattison, Chris. Frogs and Toads of the World. New York: Facts On File Publications, 1987.

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

Schiotz, Arne. Treefrogs of Africa. Frankfort am Main, Germany: Edition Chimaira, 1999.

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

Wager, Vincent A. The Frogs of South Africa. Johannesburg, South Africa: Purnell and Sons (S.A.) Pty., Ltd., 1965.

Web sites:

"African Tree Frogs (Hyperoliidae): Herpetology." Chemistry Biology Pharmacy Information Center.http://www.infochembio.ethz.ch/links/en/zool_kriecht_froesche_laub_afrikan.html (accessed on May 10, 2005).

"Family Hyperoliidae (African tree frogs)." Animal Diversity Web.http://animaldiversity.ummz.umich.edu/site/accounts/pictures/Hyperoliidae.html (accessed on May 10, 2005).

Heying, H. "Family Hyperoliidae (African tree frogs)." Animal Diversity Web.http://animaldiversity.ummz.umich.edu/site/accounts/information/Hyperoliidae.html (accessed on May 10, 2005).

Opisthothylax immaculatus. AmphibiaWeb. http://elib.cs.berkeley.edu/cgi-bin/amphib_query?query_src=aw_lists_alpha_&where-genus=Opisthothylax&where-species=immaculatus (accessed on May 10, 2005).

Razzetti, Edoardo R., and Charles Andekia Msuya. Field Guide to the Amphibians and Reptiles of Arusha National Park (Tanzania).http://www.gli.cas.cz/SEH/files/tanzie2002.pdf (accessed on May 16, 2005).