Animal life in the rain forest is as diverse as its plant life because the warm temperatures and plentiful moisture aid survival. Most animals live in the trees, especially in the high canopy.
Microorganisms can not be seen without the aid of a microscope. Bacteria are microorganisms that are always present in forest soil. They help decompose dead plant and animal matter. They grow quickly in the warm, humid rain forest environment where they feed on the leaves, twigs, and other matter that falls from the canopy.
Animals without backbones are called invertebrates. They include simple animals such as worms, and more complex animals such as the click beetle or the trapdoor spider. Certain groups of invertebrates, such as mosquitos, must spend part of their lives in water. Generally speaking, these types are not found in the trees, but in streams or in pools of rainwater. However, the humid rain forest is the ideal environment for many soft-bodied invertebrates, such as leeches, because there is little danger of drying out.
Many invertebrates eat plants or decaying animal matter. The larvae of insects, such as caterpillars, are the primary leaf eaters. Weevils drill holes and lay their eggs in nuts, which their larvae use for food. Bees gather pollen and nectar (sweet liquid) from flowers, as do butterflies and moths. The arachnids (spiders), which are carnivores (meat eaters), prey on insects and sometimes, if the spiders are big enough, small lizards, mice, and birds.
Most invertebrates have a four-part life cycle. The first stage of this cycle is spent as an egg. The egg shell is usually tough and resistant to long dry spells in tropical climates. After a rain and during a period of plant growth, the egg hatches. The second stage is the larva, which may actually be divided into several stages between which there is a shedding of the outer skin as the larva increases in size. Larvae often spend their stage below the ground, where it is cooler and more moist than on the surface. The pupal, or third stage, is spent hibernating within a casing, like a cocoon. When the animal emerges from this casing, it is an adult.
Invertebrates remain the least known variety of life in the rain forest. Among those that have been identified are such species as the Hercules beetle, the forest termite, the orchid bee, the Queen Alexandra's birdwing butterfly, the postman butterfly, and the blue hunting wasp.
Postman butterfly: The postman butterfly lives in jungles of Central America. In its larval state as a spiny caterpillar, it is a voracious eater with a preference for the passionflower vine. The adult butterfly feeds on this vine's protein-rich pollen as well as nectar, and the added protein gives it a longer lifespan than most butterflies, usually from six to nine months. Because the passionflower is a highly poisonous plant, female butterflies lay their eggs on its youngest leaves, which contain less poison. As the larvae grow, they gradually absorb some of the poison and become immune to it.
Blue hunting wasp: The blue hunting wasp prefers dining on crickets, which it hunts by flying low over the forest floor. It grips a victim in powerful jaws and then paralyzes it with its stinger. Female wasps drag a paralyzed victim into a burrow and then lay their eggs on it so their larvae have food when they hatch.
Army ant: Because they travel in huge colonies of up to 20,000,000 individuals, army ants are some of the most feared residents of the rain forest. Although they will sting, bite, and usually eat anything in their path, their colony travels at a rate of only about 1 foot (30 centimeters) per hour, and most animals can get out of their way.
Unlike other ants, army ants have no permanent nest but take shelter at night by linking themselves together with their strong claws beneath fallen leaves and trees. When they are on the march, worker ants carry any developing larvae with them.
Amphibians are vertebrates (animals with a backbone) that usually spend part, if not most, of their lives in water. Frogs, toads, and salamanders are all amphibians, and they live in significant numbers in rain forests where humid conditions are ideal. Amphibians are cold-blooded, which means their bodies are about the same temperature as their environment. In the rain forest, because the temperature is always warm, they can be active year-round.
Because amphibians breathe through their skin, and only moist skin can absorb oxygen, they must usually remain close to a water source. Mating, egg-laying, and young-adulthood all take place in ponds, lakes, or pools of rainwater. When they mature, amphibians leave the pools for dry land where they feed on both plants and insects.
Adult amphibians are usually carnivorous, feeding on insects, slugs, and worms. Salamanders that live in the water suck their prey into their mouths. Those that live on land have long, sticky tongues that capture food. Salamander larvae are mostly herbivorous, feeding on vegetation. Frogs and toads feed on algae, plants, and insects such as mosquitoes.
Mating and egg-laying for amphibians must take place in water, for male sperm are deposited in the water and must be able to swim to the eggs in order to penetrate them. Some amphibians lay their eggs in the cups of plants where water has collected and where insect larvae may also grow, a ready source of food. As the young develop into larvae and young adults, they often have gills for breathing and they, too, require a watery habitat.
Amphibians commonly found in rain forests include tree frogs and arrow-poison frogs.
Tree frogs: Tree frogs are common in the rain forest. Some, such as the Malaysian flying frog, may leap out of a tree to escape a predator. Webs of skin between their limbs act like parachutes, enabling them to glide from one branch to another. Other species of tree frogs have suction pads on their toes that secrete a sticky mucus, enabling the frog to cling to tree trunks and branches.
Arrow-poison frogs: Arrow-poison frogs are usually brightly colored. This color warns potential predators that to bite the frog may mean their death. Only a tiny drop of the poison can kill an animal the size of a dog. Arrow-poison frogs got their name from the fact that South American Indians hold them over a flame until the poison oozes out of the skin. They then dip their arrows in the poison.
Reptiles that live in rain forests include primarily snakes and lizards. The body temperature of reptiles changes with the temperature of the surrounding air, and the warm, humid rain forest is a comfortable environment for them.
Many rain forest reptiles are capable of camouflage (KAH-mah-flahj), or protective coloration. Their skins are often patterned or colored to resemble the forest background in which they live, and they may be able to alter their coloration to a darker or lighter shade. Most reptiles that live in the forest canopy have a prehensile (grasping) tail that helps them climb and may prevent falls. Rain forest reptiles may also have grasping claws to ensure a firm, steady hold as they climb through the trees.
The diet of lizards varies, depending upon the species. Some have long tongues with sticky tips for catching insects, while others eat small mammals and birds. The water they need is usually obtained from the food they eat.
All snakes are carnivores, and one good meal will last them for days or weeks. The more evolved snakes kill their prey with venom (poison) injected through their fangs.
Most reptiles lay eggs, and while some females remain with the eggs, most bury them in a hole and abandon them. The young are left to hatch by themselves. Snakes that live in the canopy, however, often bear live young. They produce fewer babies, but the babies, being mobile, have a better chance of survival.
Common rain forest snakes include the vine snake of West Africa, the bushmaster and fer-de-lance of Central and South America, the gaboon viper of Asia, and many tree snakes. Lizards include the Jesus Christ lizard of Central America, the crested water dragon of Asia, Parson's chameleon of Africa, and the Komodo dragon of Indonesia.
Chameleon: The chameleon (kuh-MEEL-yuhn) lizard is an expert at camouflage. A resident of the canopy, it can change its coloration to resemble that of the leaves, and it may even tremble slightly to mimic leaves swaying in a breeze. Its feet and tail are perfect for grabbing hold of tree limbs, and its long, sticky tongue flicks out with amazing speed to catch the insects that make up its diet.
Tree snake: Many species of tree snakes are found in rain forests. The emerald tree boa of the Amazon region is a constrictor. It has no poison but strangles its prey, usually small rodents, birds, and lizards, in its muscular coils. Its bright green coloration helps hide it from predators, such as eagles. Some tree snakes mimic twigs and branches. Those with a prehensile tail use it to anchor themselves while the rest of the body shoots forward in a strike. The flying snake of Southeast Asia flattens its body and glides as far as 165 feet (50 meters) from one tree to another.
Komodo dragon: The Komodo dragon, the world's largest lizard, is found in Indonesia, especially on Komodo Island for which it is named. Komodo dragons can measure up to 10 feet (3 meters) in length and weigh up to 300 pounds (136 kilograms). Komodo dragons are carnivores and will eat animals as large as small deer or humans and even other Komodo dragons, as well as eggs and carrion (dead bodies). They have long, sharp claws and jagged teeth that enable them to tear meat from their prey.
All rain forests have large bird populations, more than any other biome. Most do not need the protection of camouflage, and their feathers are usually brilliantly colored. Their songs vary from the scream of the eagle to the haunting warble of many smaller birds, and bower birds and pittas seem to be able to "throw" their voices like ventriloquists.
Because the vegetation is so dense, rain forest birds have developed short, broad wings that do not require much room for flying. Some species, such as toucans and parrots, have feet adapted to climbing.
Rain forest birds may fly considerable distances in search of trees bearing fruit. Different birds seek food in different layers of the forest. Parrots, for example, hunt for seeds in the canopy and insects along the trunks of the trees, while pittas dig around on the ground for snails and ants.
Birds reproduce by laying eggs, for which many species, such as the bird of paradise, build a nest. Some, however, such as the macaw, prefer to use a hole in a tree. Females usually sit on the eggs until the young birds hatch. The female hornbill of Southeast Asia actually walls herself into a hole with mud and other materials and the male feeds her until the young can leave the nest. Both parents of most species usually feed their young until they are able to fly. Some young birds, such as the hoatzin of the Amazon region, are uniquely adapted to life in the forest. The hoatzin chicks have two claws on each wing, enabling them to climb through the branches.
Common birds of the rain forests include toucans, hummingbirds, birds of paradise, jacamars, eagles, parrots, and junglefowl.
Harpy eagle: Harpy eagles live high in the forest canopy of Central and South America, often sitting in one of the emergent trees where their sharp eyes can spot likely prey. Harpies do not soar high above, but move from tree to tree in short flights. Their large nests are built of sticks, leaves, and fur about 165 feet (50 meters) above the ground, and the females produce two eggs. Harpies like to catch monkeys or sloths in their huge talons, and, if their victim attempts to cling to a tree, they are strong enough to wrench the victim free.
Parrot: Parrots are brightly colored birds with a loud, harsh call. More than 100 species live in rain forests in South America, Australia, Asia, and Africa. They tend to be social and roost in large groups. Their feet are so strong it is possible for them to hang upside down from a branch for long periods. Their nests are usually in holes in trees, where the female sits on the eggs, and the male brings her food. Preferring to eat seeds, parrots use their tongues to position a seed at the front of the strong, hooked beak and then crack the seed apart.
Junglefowl: The junglefowl of Asia is the ancestor of the chicken and, as such, has affected human life more than any other bird. Male junglefowl crow like roosters and have a red comb. In the wild, they are very aggressive; much of this behavior has been bred out of the domesticated species over the years. They live primarily on the forest floor where they feed on seeds, fruits, berries, and insects. They are good runners, but their flight is weak and apt to send them crashing into tree trunks.
Mammals of all kinds live in the rain forest, from the monkeys that swing from the tops of its trees to the shrews that scamper about the jungle floor.
Small mammals, such as the fawn-footed melomys (a type of rodent) often eat plants and insects. Herbivores (plant eaters), such as the agouti, the paca, and the royal antelope, feed on leaf buds and fruit. Cats, such as the palm civet, the ocelot, and the servaline genet, are carnivores. Many mammals, such as the orangutan, are omnivores, which means they eat both plant and animal foods.
The young of mammals develop inside the mother's body, where they are protected from predators. Mammals produce milk to feed their young, and those that live in dens must remain nearby until the young can survive on their own.
Common rain forest mammals include monkeys, kinkajous, coatis, bats, sloths, okapis, gorillas, and jaguars.
Bat: Bats are the only mammals truly capable of flight, which they do primarily at night. During the day, they sleep hanging upside-down from branches or holes in trees. Some species are very social and roost in groups of 100 or more. At night they leave their roosts to seek food. The diet of rain forest bats is either insects or flower nectar and fruits, and many trees are dependent upon them as an aid in pollination.
Sloth: Sloths are slow-moving creatures with large claws that spend their lives hanging upside-down from tree limbs in Central and South America. Adults are only about 2 feet (60 centimeters) long, but the claws by which they grip the trees measure about 3 inches (7.6 centimeters). Sloths are so well adapted to their life upside-down that even their hair grows that way, from stomach to spine. They are herbivores that almost never leave the trees because, on the ground, a sloth cannot stand or walk but tumbles over helplessly.
Okapi: The okapi, a short-necked relative of the giraffe that lives in the rain forest of eastern Congo, was not discovered by European explorers until 1901. It feeds on understory vegetation, and its tongue is so long it can be used to clean its own eyelids. The coat is purplish brown, with black and white stripes on the upper legs and buttocks. Okapis are unusual in that females are larger than males.
Gorilla: Gorillas are found only in Africa, where there are three species: the western lowland gorilla, the mountain gorilla, and the eastern lowland gorilla. These types vary slightly in physical characteristics, such as color.
The gorilla is the world's largest living primate (group of animals including apes, monkeys, and humans). Males may be as tall as 6 feet (180 centimeters) and weigh between 300 and 400 pounds (135 and 180 kilograms). Although males may beat their chests when threatened, gorillas are not usually aggressive. They spend most of their day, apart from a midday rest period, foraging for food, primarily nuts, berries, fruits, and leaves.
Jaguar: The jaguar is the largest cat found in either North or South America. A male jaguar may be 6 feet (1.8 meters) in length, with a 2-foot (75-centimeter)-long tail, and may weigh more than 300 pounds (135 kilograms). It has a tan coat and is spotted like a leopard, which helps conceal its presence in the jungle. Jaguars feed on both small and large animals. They like to wait silently in the branches of a tree and then drop down on their prey as it passes underneath.
The list of endangered rain forest animals is long, and only a few representatives can be given here. Many species of parrots are endangered, especially in Central and South America, because they are sought by animal dealers to sell as pets and because their habitat is disappearing. An example is the Spix's macaws (a species of parrot) found in Brazil. Only one male remains alive in the wild. About 30 birds live in captivity, and some females are being reintroduced into the wild in hopes that they will mate with the lone male. The helmeted hornbill of Southeast Asia is hunted for its "helmet," a horny outgrowth along the top of the bill, which is often carved into snuff boxes and buckles.
Sumatran orangutans and gorillas are in danger because they require deep forest cover, and their habitat is rapidly disappearing. For some, their only hope of preservation seems to be zoos and wildlife sanctuaries. Many rain forest cats are also endangered. They have been hunted so extensively for their skins that, although many are now protected, their numbers are so low that there may not be enough animals left for successful breeding.
Only 11,000 rhinoceroses remain in the world. Although protected, they are threatened by poachers who kill them for their horn, and by the loss of their habitat. It takes up to 250 acres (100 hectares) to support a single rhino, and they must compete with humans and their livestock for food.
Source: "Rain Forest." U·X·L Encyclopedia of Biomes, Vol. 2. U·X·L, Detroit: 2000.