Frog (animal).

« which means that their body temperature depends on the temperature of the surrounding environment.

Few species can tolerate temperatures below 4°C (40°F) orabove 40°C (104°F), and many species can survive only within a narrower range of temperatures.

In addition, frogs’ thin, moist skin offers little protection againstwater loss, and when on land the animals must guard against drying out.

Many frogs are active at night because temperatures are cooler and humidity is higher thanduring the day.

In seasonal environments, frogs may remain dormant for months at a time when conditions are inappropriate.

For example, many frogs that live wherethe winters are cold spend the winter months buried in the mud at the bottom of a pond, and desert-dwelling species may burrow under the sand during the dry seasonor to escape extreme heat.

Frogs do not drink, but they can replace lost water by absorbing it through the skin.

A frog may sit in water or completely submerge toreplenish moisture in its body.

When a frog sits on moist ground, it absorbs water through the skin on its belly and the underside of its hind legs. On land, frogs move from place to place by jumping, and some species, especially toads, move by crawling.

Jumping enables frogs to move rapidly over land withoutleaving a scent trail, helping them escape from predators such as bats, herons, raccoons, snakes, turtles, fish, and even tarantulas.

Although frogs escape frompredators by jumping, they typically catch their own prey by simply sitting in one place and waiting.

Most frogs feed on insects and other small invertebrates, such asworms, spiders, and centipedes.

Aquatic frogs sometimes eat other frogs, tadpoles, and small fish.

Larger frogs eat animals as large as mice or small snakes.

When afrog sees that an insect or other prey animal is within range, it rapidly flips out its tongue, which is attached at the front of the mouth and catapults over the lower jaw.The tongue is coated with a sticky substance that holds on to the prey.

Frogs generally swallow their prey whole.

When a frog swallows, its eyes sink down throughholes in the skull and help push food down the throat. Frogs advertise their presence and communicate with other frogs using a variety of complex calls, including ribbets, croaks, and other sounds.

They produce thesesounds in much the same way as humans speak, by forcing air from their lungs over their vocal cords, located in the throat.

Frog communication is particularlyimportant during the mating season, when male frogs call to attract females ( see Animal Courtship and Mating).

The males of many species possess vocal sacs, expandable pouches of skin in the throat or on each side of the mouth.

When the frog calls, the vocal sacs inflate and act as resonating chambers, amplifying thevolume of the call.

Each frog species has a distinctive call, enabling females to find an appropriate mate even when several different species are calling and breeding inthe same area at once.

If a female frog is clasped by a male that she does not want to mate with, she may give a call that tells the male to release her. The breeding behavior of frogs is extremely variable.

Some species congregate in large numbers around a pond, where they breed and lay their eggs in the water.Typically, after the female enters the water, the male frog positions himself behind her and grasps her by the waist.

Once a suitable egg-laying site has been found, hereleases sperm as she releases eggs, and fertilization—or union of the sperm and egg—takes place outside the body.

Other species breed on land, and here again themale clasps the female from behind, releasing sperm as she lays her eggs on trees or other vegetation.

Some male frogs are territorial during the breeding season,engaging in biting or wrestling combat with other males to compete for females. Most frogs do not care for their young—the adults simply mate and abandon the eggs.

A few frogs provide varying degrees of parental care, of which there are somespectacular examples.

Either the male or the female may provide this care, depending on the species.

Among some frogs one of the parents stays near the clutch ofeggs and guards it from harm.

The female marsupial frog takes her eggs with her, incubating them in a pouch on her back.

In one Australian frog species, the femaleswallows the eggs and the young develop in her stomach and emerge from her mouth as tadpoles or froglets.

In Darwin’s frog, the male cares for the young, carryingthe eggs and tadpoles in his vocal sac until they have matured into adults. V LIFE CYCLE Most frogs undergo a two-stage life cycle.

Eggs hatch into fishlike young called tadpoles, which grow and eventually undergo metamorphosis, a change in body form, tobecome adults.

Frogs have developed many variations on this common theme, and a few species provide striking exceptions to the rule.

For example, frogs in thetropical genus Eleutherodactylus do not have a tadpole stage.

Instead, tiny froglets hatch directly from the eggs.

In the African toad, fertilization occurs internally, and the young are born alive. Frogs often produce large numbers of eggs—up to 10,000 or more—surrounded by a jellylike coating that protects the eggs from predators and keeps them fromdrying out.

Those that provide some degree of care for their young usually produce relatively few eggs.

Species that breed in ponds typically lay their eggs in clumps orstrings in the water.

Those that breed in streams often attach their eggs to the undersides of rocks.

Others construct foamy nests in the water or on vegetation nearthe water.

Some frogs even attach their eggs to the undersides of leaves that hang over the water.

When these tadpoles hatch, they drop into the water below.

Manyspecies lay their eggs in water trapped in tree cavities or cup-shaped parts of plants.

In warmer climates, eggs may hatch within 1 or 2 days, while in colderenvironments they may take 30 to 40 days to hatch. Tadpoles, which usually live in water, look somewhat like small fish.

A tadpole has an oval body, gills for breathing, and a long, muscular tail with fins along the upperand lower edges for swimming.

Tadpoles have two small eyes, one on each side of the head.

A tadpole’s mouth has a horny beak and rows of tiny, comblike teeth thatthe animal uses to scrape algae from underwater plants and bite off bits of plant material.

In a few species, tadpoles eat the eggs and tadpoles of other frogs.

Tadpolespump water through their mouths, over the gills, and out through an opening called the spiracle, which is usually located on the left side of the body.

The gills extractoxygen from the water.

The tadpole stage lasts anywhere from a few weeks in species that lay eggs in temporary ponds to three years in the bullfrog.

Typically, frogsspend a few months as tadpoles before metamorphosing into adults. Metamorphosis involves radical changes in both external and internal body parts.

The tadpole grows legs—the hind legs appear first—and resorbs its tail.

It loses its gillsand grows lungs, and the structure of the heart, digestive system, and skeleton changes.

The horny beak and other mouthparts adapted for eating algae disappear andare replaced by the long, sticky, projectile tongue that helps adult frogs catch insects.

Frogs reach reproductive age anywhere from several months to several yearsafter metamorphosing.

Most frogs probably live only a year or two in the wild, but bullfrogs live several years, and the African clawed frog has been known to live 35years in captivity. VI FROGS AT RISK Since around 1980, scientists have reported startling declines in the populations of some species of frogs.

These declines have occurred around the world, affectingfrogs from California, Australia, the Andes of South America, and other parts of the globe.

Some of these declines may reflect natural fluctuations, but scientists believemany frog species are in trouble because of environmental changes caused by humans.

Pollution or destruction of frog habitat due to logging, industry, or developmentmay be responsible for some population declines. However, frogs are also disappearing from relatively untouched habitats.

The golden toad of Costa Rica and the gastric brooding frog of Australia have recently becomeextinct, despite the fact that they are native to still-pristine wilderness areas.

The disappearance of these and other species has baffled scientists, but it is now believedthat the rapid spread of a fungus that affects the skin of amphibians is responsible for many of the more rapid declines.

The chytrid fungus causes the diseasechytridiomycosis, which can be deadly to frogs and other amphibians.

Scientists also fear that global environmental changes such as acid rain, global warming, andincreased levels of ultraviolet radiation due to the thinning ozone layer may threaten frogs even in areas far from human disturbance. Scientists have also documented an alarmingly high occurrence of frogs with malformations such as missing or extra legs, abnormal webbing, and missing eyes.

These. »