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Red-Eyed Tree Frog

Common Name: Red-Eyed Tree Frog Scientific Name: Agalychnis callidryas Average Life Span In The Wild: 5 years Size relative to a teacup: IUCN Red List Status:? Least concern

Least Concern Extinct

Current Population Trend: Decreasing

Many scientists believe the red-eyed tree frog developed its vivid scarlet peepers to shock predators into at least briefly questioning their meal choice.

Colorful Adaptations

These iconic rain-forest amphibians sleep by day stuck to leaf-bottoms with their eyes closed and body markings covered. When disturbed, they flash their bulging red eyes and reveal their huge, webbed orange feet and bright blue-and-yellow flanks. This technique, called startle coloration, may give a bird or snake pause, offering a precious instant for the frog to spring to safety.

Their neon-green bodies may play a similar role in thwarting predators. Many of the animals that eat red-eyed tree frogs are nocturnal hunters that use keen eyesight to find prey. The shocking colors of this frog may over-stimulate a predator's eyes, creating a confusing ghost image that remains behind as the frog jumps away.

Range and Habitat

Red-eyed tree frogs, despite their conspicuous coloration, are not venomous. They are found in tropical lowlands from southern Mexico, throughout Central America, and in northern South America. Nocturnal carnivores, they hide in the rain forest canopy and ambush crickets, flies, and moths with their long, sticky tongues.

Red-eyed tree frogs are not endangered. But their habitat is shrinking at an alarming rate, and their highly recognizable image is often used to promote the cause of saving the world's rain forests.

Why Do Tree Frogs Lay Their Eggs On The Ground?

image:

A tree frog: female (larger individual below) laying eggs, which are protected by the 'foam nest' and male (smaller individual above).

Credit: Ichioka Yukio

When it comes to laying eggs, tree frogs have some unusual habits. Instead of always laying their eggs on tree branches where they usually live, they often lay their eggs on the ground. But why would a tree frog do this, especially when it puts its eggs at risk from predators such as snakes?

To solve this puzzle, a team from Nagoya University in Japan studied the spawning behavior of the forest green tree frog (Zhangixalus arboreus), a species commonly found in Japanese forests. They found that the frog's behavior is likely part of a strategy to avoid the colder environment in tree branches in favor of a warmer environment on the ground. They reported their findings in Ecology and Evolution.

Tree frogs create distinctive "foam nests" by bubbling secretions from their bodies to protect their eggs. The foam nest is usually white or light in color, resembling a mass of small bubbles clustered together. These amazing amphibians create their nests by whipping air into a secretion from their body that produces a foamy, frothy substance. These nests are essential to protect developing eggs and embryos by providing a stable and biocompatible environment that also offers protection from predators.

When building their nests, tree frogs use a mixed strategy. Sometimes the frogs build nests on the ground and sometimes they build them on tree branches overhanging ponds and marshes. Doctoral student Yukio Ichioka from the Graduate School of Bioagricultural Sciences and his supervisor Professor Kajimura wondered why they did this.

"In some areas, we find foam nests on the ground around ponds, even though there are trees suitable for building bubble nests," lead researcher Yukio Ichioka said. "However, it was a mystery as to why they lay their eggs on the ground where they are at risk of predation by their natural enemies."

To better understand this behavior, the researchers compared the temperatures inside a sample of nests on the ground, a sample of nests on tree branches, and the environmental temperature. They also calculated the hatchability rate of eggs by counting the number of eggs that hatched into tadpoles and the number of eggs that did not.

Ichioka and Kajimura found that tree frogs employ a rather complicated egg-laying strategy. When the air temperature was low, the internal temperature in the foam nests on the ground was warmer than that of the surrounding area.

This heat retention effect was mainly demonstrated at night when the temperature was lower. The above-ground foam nests protected the eggs from low temperatures and increased the probability of hatching. This conclusion was supported by the hatchability rate of the eggs being higher at ground level than at tree level.

Their findings suggest the previously unknown adaptive significance of tree frog egg laying on the ground. That is, laying eggs on the ground protects them from the cold. This is an important behavior given that forest green tree frogs sometimes live in areas high above sea level.

"These findings will be an important contribution to understanding the evolution of spawning behavior in amphibians," said Kajimura. "They will also shed light on the adaptation strategies of forest organisms to the thermal environment. Our research is important for the relationships between climate and animal behavior and can contribute to understanding the evolution of behavior, especially in the current environment."

The researchers are keen to test their theory with other frogs. "We plan to begin research on Zhangixalus viridis in Okinawa in April 2024," Ichioka said. He is excited about the prospect of further research: "Frogs other than Z. Arboreus also make foam nests, so our findings can provide more insights into their ecology and adaptive evolution."

Journal

Ecology and Evolution

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Frogs And Toads Of New York

Most everyone recognizes frogs. Frogs, like salamanders and newts, are amphibians. Unlike salamanders, they have made a major evolutionary detour from the body plan of their ancient ancestors. The hind legs of frogs are much larger than the forelegs and the tail has disappeared. This allows a new mode of locomotion, namely jumping, an effective method to elude their many predators. Because they leave the ground to get around, using scent to communicate with each other is not a viable option, as it is for salamanders. Consequently, frogs are among the most vocal of vertebrate animals (birds fly, so they vocalize a lot as well!). Frogs in New York fall into four major groups (families) linked by anatomy and other features of their biology.

Toads

Toads are frogs that, due to the nature of their coarse dry skin, are adapted to spend most of their life on land. We have three kinds in two different families. The very common American toad is easily recognized by the warts all over its back and sides and by a pair of large bean-shaped glands are located just behind the head. These glands produce a mild poison that the toad stores in its bladder. When handled, toads will produce a copious urine with enough of this foul-tasting toxin to deter most predators. As a consequence, toads do not need to be good leapers to escape their enemies. Toads begin breeding late in April when males begin producing their long, rather musical trill. One can imitate this call by whistling and humming at the same time. Toads use all sorts of water bodies to deposit their long strings of eggs. Since hatching and tadpole development can be completed in as little as four to six weeks, toads often use temporary bodies of water to deposit eggs. This may include large puddles and deep tire tracks that hold water.

The similar Fowler's toad is found in the southeastern part of the state and on Long Island. It has many warts in each of the dark spots on its back and sides, while the American toad has one or two warts per spot.

One representative of the spadefoot toad family reaches New York, although they are restricted to the sandy-soil pine habitats of Long Island and the Pine Bush near Albany. Spadefoots can be recognized by their rather smooth skin, vertical eye pupils, and the dark hard patches of skin on their toes used for digging. They spend much of their time underground and are most active on the surface at night following heavy spring and summer rains.

Treefrogs

The only true tree frog of New York, the gray treefrog, is common over the entire region. It is most often observed in late spring and early summer when the males make their characteristic loud trilling calls. Calling sites are usually in the lower branches of trees near the water's edge. They possess large round toe pads that enable them to maintain their grip even on vertical surfaces. Adults are mostly gray with black splotches but they can change their color pattern to a degree and may appear bright green to silvery. A flash of yellow is found on the undersides of their legs.

The spring peeper is clearly one of the most common vertebrate animals in New York, found in nearly all forested habitats within a few miles of standing water. Although few have actually seen one, nearly everyone has heard the distinct, and very loud, peep these tiny frogs produce. Despite their inclusion in the treefrog family, peepers are rarely found in trees. Outside of the breeding season they may be found leaping along the forest floor in search of insects. And what a leap it is, nearly 50 times their inch and a half length! In the breeding season, male peepers gather in the weedy vegetation at the edge of ponds to call and attract females for mating.

Eggs are attached singly to underwater plants and hatch within a week. After about 45-60 days, depending partly on water temperature, the tadpoles emerge from the water and inhabit the leafy litter of the forest. Other members of the treefrog family include the northern cricket frog, found in a few areas south of the Catskills, and the western chorus frog, which occurs along the western Lake Ontario plain and the Watertown area.

Typical Frogs

The bullfrog is the clear winner in the size department among New York frogs, attaining lengths of 7 inches from snout to tailbone. The low frequency "jug-o-rum" call they produce is familiar to all May and June visitors of the region's lakes and ponds.

Like all amphibians, bullfrogs are carnivorous and they will attempt to eat anything that will fit into their considerable mouths. This includes insects, snakes, other frogs, and even birds and mammals. Like most frogs, bullfrogs are visual predators and will react by orienting their bodies towards any small movements around them. If you see a frog catch an insect, look closely and it seems like it closes its eyes as it swallows. Small muscles attached to the eyeball pull it towards the back of its throat and help force the food down into the stomach.One of the most common mid-sized frogs across New York is the green frog. They can be superabundant in marshes, ponds, lakes, and quiet backwaters of streams if their insect food supplies are also abundant. Male green frogs, like those of bullfrogs, have visible eardrums on the side of their heads that are bigger in diameter than their eye. The eardrum of females is smaller than the eye. Green frogs make at least six vocalizations, but the most often heard is the advertisement call of the male. It has been compared to plucking a banjo string.

Mink frogs may be found in the colder waters of northern New York, primarily in the Adirondacks. They are small frogs that at first glance are easily confused with the much more common green frog. Careful examination of the spotting pattern across the folded hind limbs, which appears random in mink frogs and continuous in green frogs, will distinguish the two. The presence of a strong musky odor on your hands after you release one will clinch the identification as a mink frog.

Before winter is officially over, and often while there is still ice on the ponds, a sound like quacking ducks may be heard in forest ponds and beaver flows. This is the wood frog, the first of the New York amphibians to make an appearance each year.

Wood frogs hibernate in the leaf litter of the forest floor, usually just a few inches below the surface. Scientists have learned that these frogs, as well as the spring peeper and gray treefrog, can tolerate partial freezing of their body tissues, a condition that is lethal to most animals. They accomplish this through two methods. The first entails the use of antifreeze compounds, including the same ethylene glycol we put in our automobiles, that circulates in their blood and lowers the freezing point. The second mechanism involves removing much of the water from their cells so it doesn't freeze inside the cells. When water freezes, it expands and the resulting ice could easily break apart cell membranes.

Wood frogs possess a distinctive black patch around the eyes on an otherwise brown body. Wood frogs are found throughout the forested parts of New York and may be observed quite far from water. There are two species of common dark-spotted frogs found across New York, often side by side at pond edges. The northern leopard frog is light brown to bright green with dark round spots, each with a light border, found irregularly on its back and legs. The pickerel frog has a lighter background color and squarish spots with no light border which occur in two rows down its back. There is often a distinct flash of yellow coloration on the thighs of pickerel frogs. Both are fond of the grassy and weedy borders of ponds, and are often found quite some distance from the water. Their early spring staccato calls sound like a particularly loud snore and the two species may be distinguished by the pitch of their call.

Ecological Roles

Like most organisms, frogs are vital links between food web feeding levels because they are important food sources for many other organisms. Frogs, however, play a unique role in connecting aquatic and terrestrial food webs, due to their two lifestyles. All New York frogs start life as aquatic tadpoles, feeding on plant and animal material in water. When they metamorphose into air-breathing adults, they carry some of this aquatic energy stored in their bodies and export it onto land, where it can enter new food chains.

Checklist of Frog Species Found Within New York

Eastern Spadefoot

Eastern American Toad

Fowler's Toad

Northern Cricket Frog (Threatened)

Northern Gray Treefrog

Cope's Gray Treefrog

Northern Spring Peeper

Upland Chorus Frog

Western Chorus Frog

Bullfrog

Green Frog

Mink Frog

Wood Frog

Northern Leopard Frog

Southern Leopard Frog (Special Concern)

Pickerel Frog

Fish and Amphibians