SQUEAKERS AND CRICKET FROGS: Arthroleptidae

PHYSICAL CHARACTERISTICS

The squeakers and cricket frogs have smooth skin without the large warts seen in toads and many other types of frogs. A few, like the Ugandan squeaker, have some warts, but the warts are so small that they almost look like grains of sand. Depending on the species, some of the members of this family are reddish, greenish brown, brown, or almost black. Their toes have no webs between them, but the toes in some species end in large pads. Most have thin front and back legs. A few are burrowers, though, and have heavier legs to help them dig. Some of the burrowers also have thick, shovel-like bumps, or tubercles (TOO-ber-kulz), on the heels of their hind feet, which are also used in digging. Many species in this family grow to less than 1 inch (2.5 centimeters) long from the tip of the snout to the end of the rump, but some can grow much bigger. In many species, the adult's size is enough to tell a male from a female. In some, like the crowned forest frog, the male is much larger than the female, but in others, like the common squeaker, the female is bigger than the male.

Squeakers and cricket frogs are usually split into two groups, called subfamilies, although some scientists think the two subfamilies are so different that they should instead each have their own family. Others think the squeakers and cricket frogs should not have their own family at all and should instead be combined into the large family of true frogs, known as Ranidae. Many people disagree with this idea because of the breastbone. The breastbone, or sternum, is made of bone in the true frogs, but is different in the squeakers and cricket frogs. The sternum in squeakers and cricket frogs has some flexible material, called cartilage (CAR-tih-lej), in it. In this volume the squeakers and cricket frogs are all listed together in one family, separate from the true frogs. Inside this family are two subfamilies.

The larger of the two subfamilies is called Arthroleptinae and contains about two-thirds of the 77 species in the entire family. This group includes such species as the common squeaker, Tanner's litter frog, the Bush squeaker, and the Ugandan squeaker. Some of the features that most of these frogs share are a thin crease or ridge of skin that runs down the middle of the back and a dark pattern on the back that may be a row of diamonds, an hourglass, or something similar. The back of Tanner's litter frog, for instance, has a row of V-shaped markings. These patterns may be difficult to see on very dark-colored frogs.

The adult males also have a very long third toe on each of their front feet. Toes are counted from the inside to the outside, or from the big toe to the little toe, if compared to humans. This third toe on the West African screeching frog is as long as its thigh. In some species, the toe may be almost half as long as the frog's entire body. Many of the frogs in this subfamily, which as a group are called arthroleptins, have no teeth. Most of these frogs are small, but the female Tanner's litter frog grows to 2.4 inches (6 centimeters) in length, sometimes longer.

MY HOME, MY RAINFOREST

Like thousands of other animals, many squeakers and cricket frogs live in only one place in the world: a tiny spot inside a rainforest. Scientists often do not know much about these animals because rainforests are typically so thick with plants that animals—especially small, secretive species like frogs—can easily remain hidden from sight. People, however, are removing more and more of the rainforests to make the land into farms or to use wood from the trees for building. Since some of the rainforest animals live in very small areas, this kind of destruction can wipe out entire species. Conservationists are now trying to save the rainforests and, in doing so, protect the animals that live there.

The second subfamily is called Astylosterninae and contains species like the crowned forest frog and the hairy frog, among others. Most of the frogs in this group have large bodies. The male crowned forest frog, for instance, grows to 2.7 inches long, and the male hairy frog can reach 5.2 inches in length. In both of these species, the males are bigger than the females. Members of this subfamily also have sharp, curved bones at the ends of their front toes. These bones poke out of the flesh at the tips of the toes, and sometimes look like claws. The front toes are also usually bent. All of these frogs have teeth on the upper jaw.

GEOGRAPHIC RANGE

The squeakers and cricket frogs are found throughout much of central to southern Africa, but not in the southwest portion of the continent. Some live in lowland forests and others in mountains up to 9,800 feet (3,000 meters) above sea level.

HABITAT

Squeakers and cricket frogs live in hot and humid tropical forests, where they spend much of their time under dead and rotting leaves on the forest floor. Sometimes, those in the subfamily Arthroleptinae will also make their homes in fields that have a good cover of leaves on the ground. Frogs in this subfamily live and breed on land. Members of the other subfamily, Astylosterninae, remain on land for most of the year, often in mountain forests. Some, like the Nsoung long-fingered frogs, hide on land under rocks and stones. Member of this subfamily move into fast-flowing streams and rivers to breed, but they usually stay in calm areas and not in the rushing current.

DIET

The smaller frogs in this family eat invertebrates (in-VER-teh-brehts), which are animals without backbones. In particular, they eat tiny insects, spiders, and other arthropods (AR-throe-pawds). Arthropods are invertebrates that have jointed legs. The larger frogs will eat bigger prey, often anything they can find, capture, and stuff into their mouths. Sometimes, this includes other small frogs.

BEHAVIOR AND REPRODUCTION

For many of the squeakers and cricket frogs, time is spent mainly searching along the forest floor, or the shores of streams and rivers, for something to eat. Some, like Tanner's litter frog, hunt by ambush. In this type of hunting, the frog sits very still in one place, waits for an unsuspecting insect or spider to wander past, and quickly grabs and eats it. Other species, including the Ugandan squeaker, take a more active role and slowly move along the ground looking for insects to eat.

Those frogs that live in meadows and in bright, open forests usually stay out of sight during the day and do their hunting at night. Others that live in thick, shady forests may venture out during the daytime, as well as at night. Whether they are active only at night, or during both night and day, squeakers and cricket frogs will seek shelter under leaves if the weather becomes too dry and stay there until it rains again. Some species dig burrows and remain underground instead. This period when the frogs rest and wait for less-dry weather is called estivation (es-tih-VAY-shun).

The frogs mate during the rainy season, when storms soak the land. Squeakers and cricket frogs are named for the sounds of their calls. Some, like the West African screeching frog, have a little flutter in their calls. The West African screeching frog has a high call that lasts less than a second. Many people think this species, and others with calls like it, sounds like crickets. The common squeaker has a short high peep of a call. The calls of the males in each species draw in females of the same species. Those frogs in the subfamily Arthroleptinae mate and lay their eggs in a moist spot on land. The female Tanner's litter frog, for instance, lays about thirty eggs in a small dip in the ground underneath the leaves.

The female Bush squeaker follows the male's long, high "wheep" or "wheepee" call, pairs with him, and lays eleven to eighty eggs under leaves at the base of a bush or other thick, leafy plant. In some species, like the Ugandan squeaker, the female may lay more than one batch of eggs in one breeding period. Since this species only lives for about six months, these two or more sets of eggs are the only young she will have. The female West African screeching frog also lays more than one set of eggs in a breeding season. In each of her two or three clutches, she usually lays ten to thirty eggs. Like the Ugandan squeaker, the West African screeching frog only lives for about six months.

The eggs of most members of this subfamily are each covered in a capsule of gel. The gel provides extra moisture for the baby frog developing inside. While it is growing inside the egg, scientists call the frog an embryo (EHM-bree-oh). They use this same word to describe other types of animals, such as chickens, snakes, and lizards, while they are inside the egg. In squeakers and cricket frogs, the embryo must remain moist. If the egg were to dry out, the embryo would die. These eggs typically have a large yolk, which feeds the growing embryo until the egg hatches.

In some species, an adult stays with the eggs until they hatch. Bush squeakers are one of the species that have this type of care for the eggs. Instead of hatching into tadpoles, the eggs of the frogs in this subfamily hatch right into froglets. The froglets usually look much like the adults. The froglets of the West African screeching frog, for example, have the same dark, hourglass-shaped pattern on their backs as the adults do. By the time they are three months old, these froglets are old enough to reproduce themselves.

Frogs in the subfamily Astylosterninae do things a bit differently. Instead of mating and laying their eggs on land, they mate and lay their eggs in a fast-flowing stream or river. The males select a spot off to the side where the water is calm, and they mate with females there. The females lay their eggs in the water. In some species, like the hairy frog, the male stays with the sunken eggs until they hatch. The eggs of species in this subfamily hatch into tadpoles, which usually head out of the calm water and into the rushing flow. Some tadpoles, like those of the hairy frog, have large suckers, which the tadpoles use to grab onto rocks and other surfaces, and fight the current. Other tadpoles, like those of the crowned forest frog, have no suckers, but still swim into the fast waters of the stream or river. The tadpoles change into froglets, which then leave the water for a life on land.

SQUEAKERS, CRICKET FROGS, AND PEOPLE

Some people hunt for and eat the larger species of squeakers and cricket frogs. They do not bother the smaller species. Squeakers and cricket frogs are rare in the pet trade.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists two species, the cave squeaker and the Nsoung long-fingered frog, as being Critically Endangered. Critically Endangered species face an extremely high risk of extinction in the wild. Both the cave squeaker and the Nsoung long-fingered frog live in very small areas. In the case of the cave squeaker, all of the individuals appear to live in just one area in the mountains of eastern Zimbabwe. Scientists have only seen this frog once, when it was first discovered in 1962 in a grassy field and nearby caves on the mountain. This spot on the mountain is part of a national park. Nsoung long-fingered frogs are scattered over several spots in western Cameroon, all of which are high on the south side of a mountain. People have begun cutting down the nearby forests to make way for farmland and other uses. If the frog's tiny habitat is also lost, the frog will be in danger of extinction.

The IUCN lists nine other species as Endangered and facing a very high risk of extinction in the wild. All of the nine species are found only in small areas on mountains. One species lives in Guinea, one in Malawi, one in Tanzania, one in Sierre Leone, three in Cameroon and Nigeria, and two in just Cameroon. In many cases, these species are split up into small groups, each of which lives far away from the others. When a species is separated like this, scientists term it fragmented. In other words, the species is divided into small pieces, or fragments. This is usually not healthy for a species, because the males and females have no chance to mate with males and females from other groups. After many generations of breeding within the same group, some of the young may begin to have birth defects that can be fatal. This problem is seen in other types of animals too. Conservationists also are concerned because the endangered frogs all live in habitats that are being threatened by logging, clearing of the land for farming, or other human activities.

The IUCN considers two more species to be Vulnerable and facing a high risk of extinction in the wild; and three to be Near Threatened, which means they are at risk of becoming threatened with extinction in the future. In addition, it names sixteen as Data Deficient, which means that too little information is available to make a judgment about the threat of extinction. Often, this Data Deficient category is used for species that scientists have heard about, but have not yet studied in any detail. In the case of the squeakers and cricket frogs, more than one-fifth of the 77 species in this family fall under the Data Deficient category.

COMMON SQUEAKER (Arthroleptis stenodactylus): SPECIES ACCOUNTS

Physical characteristics: The common squeaker is sometimes called a dune squeaker or savanna squeaking frog. It is a brown or copper-colored frog with a faded, darker brown pattern on its back that looks something like an hourglass. It has two dark brown spots near the rump and sometimes a thin, lighter-colored stripe running down the middle of the back. It also has dark brown bands on its thin legs. The front legs are quite long compared to the front legs of other frogs, while the rear legs are rather short when compared to many other frogs. It has quite long toes, but no webbing between them. A dark brown line or patch runs from the snout down each side of its face and to its front legs. Its belly is whitish, often with noticeable but small gray blotches. It has a plump body. Its wide head narrows toward the front, and it has two large, bulging eyes. It is also known as the shovel-footed squeaker because it has a large, rough bump, or tubercle, on each of its back feet. This tubercle, which has a shape something like the edge of a shovel blade, is as long as its first toe. Females and males look much alike, although the male frog has a black throat and a much longer third toe on the front foot. Toes are counted from the inside toe (in humans, the big toe) out. In addition, females are usually larger overall. Females grow to about 1.8 inches (4.5 centimeters) from snout to rump, while males reach about 1.3 inches (3.3 centimeters) when full grown.

Geographic range: The common squeaker lives in much of the southern half of Africa, including parts of the Democratic Republic of the Congo, Kenya, northern South Africa, Zimbabwe, and Mozambique.

Habitat: The common squeaker typically makes its home along the coast in sandy-soiled forests where dead leaves cover the ground. It can live in lowland forests or quite high up on mountainsides. In all, it has been found in places that are from 130 to 6,600 feet (40 to 2,000 meters) above sea level.

Diet: Common squeakers eat many different types of invertebrates, including insects, earthworms, and snails. They may also eat a small frog once in a while.

Behavior and reproduction: When the weather is dry, this frog often stays hidden under damp, dead leaves that lie on the forest floor or beneath grasses in fields. When it rains, however, it will come out during the daytime or at night to look for its next meal. In the breeding season, which is also during the rainy season, the males may use these same hiding places to call day and night for females. The call is a quick, high-pitched peep, similar to the sound a squeaky wheel might make as it spins around. The females lay their eggs in damp places, including little dips in the ground and burrows that are typically under layers of rotting leaves or in tangles of roots at the base of a tree. A female lays about thirty-three to eighty eggs at a time. The eggs are white, about 0.1 inches (2.5 millimeters) in diameter, and are each surrounded in gel. In about one month, these eggs hatch right into froglets, skipping the tadpole stage seen in many other frogs.

Common squeakers and people: The common squeaker does quite well around humans and is often found in gardens. People do not hunt this frog, and it is not common in the pet trade.

Conservation status: The World Conservation Union (IUCN) dos not consider the common squeaker to be at risk. It is very common and found over a large area, including some protected places where logging and other human activities are not allowed. ∎

HAIRY FROG (Trichobatrachus robustus): SPECIES ACCOUNTS

Physical characteristics: The hairy frog is a large, heavy-bodied frog that is most known for the long frills, or "hairs," that grow only on the males and only during the mating season. These frills are actually very thin bits of flesh that develop on the male's thighs and on the sides of the body from his front legs to the rump. Frogs breathe in oxygen with their lungs and through their skin. Actually, it is the blood vessels in the skin that are able to take up the oxygen. Hairy frogs have very small lungs. Scientists believe that the male's frills help them draw in extra oxygen by giving the frogs more skin, and therefore more blood vessels, through which to breathe. This is important for the males, which need all the oxygen they can get once they mate and start caring for their young.

Males also have many rough pads on the bottoms of their unwebbed front feet. Their back feet, which are webbed, also have a few pads, but not as many as the front feet have. The pads probably help them hang onto the female during mating. They have very long toes on their back feet. Both males and females are dark greenish brown to black and have a long dark blotch down the center of the back and smaller dark spots toward the rump. In especially dark frogs, the blotch and spots may be difficult to see. Hairy frogs have a yellow throat. Males grow larger than females. Males can reach 5.2 inches (13 centimeters) long, while females reach 3.6 inches (9 centimeters) in length.

Geographic range: Hairy frogs live in the western part of central Africa, including eastern Nigeria, Cameroon, Equatorial Guinea, and parts of the Democratic Republic of the Congo and Gabon. Scientists think it may also live in Angola, although they have not seen any there yet.

Habitat: Hairy frogs especially like to make their homes in areas where thick, lush forests surround fast-flowing streams and rivers. Sometimes, the frogs live on farms, such as tea plantations, but they usually prefer mountain forests. Hairy frogs stay on land nearly all year, but enter the streams and rivers to mate.

Diet: Hairy frogs eat insects and other arthropods that they find along the ground of the forest and the shores of streams.

Behavior and reproduction: Hairy frogs spend most of the year hopping along the forest floor looking for things to eat. When the rainy season comes, their attention turns to mating. Males enter streams and sometimes rivers that have a fast current, but they stay in a quiet spot where the water is very still. After spending a few extra days in the forest, the females join the males in the streams and rivers and mate with them. During mating, the male climbs onto the female's back and holds on near her front legs while she lays her eggs. The pads on his front feet probably help him cling to her body, which is wet and quite slippery.

Each female lays her eggs in the water, and the male stays with them. Water contains oxygen, and the frog's skin, including the frills on his sides and legs, take up this oxygen so the frog can breathe even when he is completely underwater. For this reason, the male can stay beneath the surface with the eggs for days without having to come up for air. The eggs hatch into tadpoles that have a large sucker on the belly side. The sucker helps them attach to rocks and other surfaces in the water. The tadpoles continue to live there, sometimes even venturing into the tumbling foam at the bottom of small waterfalls, before turning into froglets and climbing out onto land.

Hairy frogs and people: Some people collect and eat these large frogs and even the tadpoles. In places where a great deal of hunting takes place, the frogs can become scarce.

Conservation status: Although people do hunt the frogs for their meat, the World COnservation Union (IUCN) does not consider the species to be at risk for now, because the frogs live over a fairly large area, are quite common, and are not hunted everywhere they live. Conservationists are, however, keeping a watchful eye on the frogs. Some streams and rivers where the frogs mate are becoming more polluted, and this may be killing a number of the eggs, tadpoles, and/or frogs. ∎

FOR MORE INFORMATION

Books:

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

Passmore, Neville, and Vincent Carruthers. South African Frogs: A Complete Guide. Revised edition. Halfway House, South Africa: Southern Book Publishers and Johannesburg: Witwatersrand University Press, 1995.

Rödel, Mark-Oliver. Herpetofauna of West Africa. Vol. 1, Amphibians of the West African Savanna. Frankfurt: Chimaira, 2000.

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

Web sites:

"Breathing." The Frog.http://www.thefrog.org/biology/breathing/breathing.htm (accessed on April 10, 2005).

"Common Squeaker." Herpetology Department, California Academy of Sciences.http://www.calacademy.org/research/herpetology/frogs/list6.html (accessed on April 10, 2005).

"South Malawi Montane Forest-Grassland Mosaic." World Wildlife Fund. http://www.worldwildlife.org/wildworld/profiles/terrestrial/at/at014_full.html (accessed on April 10, 2005).