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While the common perception of frogs often conjures images of semi-aquatic creatures living near pond edges and other bodies of water, there exists an exception to this stereotype—the arboreal frog.
Unlike their pond-dwelling counterparts, tree frogs are specially adapted to life in the treetops. While they share the need for moisture absorption through their skin, these agile amphibians spend the majority of their time concealed amidst the foliage.
Arboreal Frogs Overview
Arboreal is a word used to describe an animal that lives in the trees. In the case of frogs, there are more than 800 arboreal species which belong to several families. Tree frogs belong to the Hylidae family, but there are also leaf frogs (Phyllomedusidae) and bush frogs (Rhacophoridae) that are classed as arboreal.
Each of these families has its own characteristics, but they’re all specially adapted to live in an elevated habitat. More often than not, these frogs live in tropical and subtropical areas, and they can be found typically in dense forests across continents such as Africa, Asia, North and South America, and Oceania.
However, tree frogs aren’t only found right up in the canopy, although many species do live at these high elevations. Tree frogs can be found throughout the vegetation and may even be spotted in domestic gardens among taller plants. What’s more, each species’ adaptations dictate at what elevation they live, with some living in mountainous regions while others are found much closer to sea level.
One of the most fascinating things about tree frogs is their amazing coloration. Different species have different colors, and these are largely intended for camouflage. There are even some that can change color. In addition to this, many tree frog species are nocturnal which allows them to hunt for food, like insects, with a decreased risk of running into a predator such as lizards, birds, and even large fish.
If you’re in the forest at night, you’ll likely hear the loud and unique calls of the male tree frogs which they use to attract a mate. Interestingly, tree frogs can often be seen hanging upside down thanks to the circular sticky discs on their feet. This is a unique adaptation that isn’t seen in terrestrial frogs. When a tree frog is injured, it even has the ability to regenerate lost limbs by creating new tissue from a bunch of cells called a blastoma.
Not only are tree frogs incredibly interesting but they’re also important as bioindicators. Their presence in an area tells us a lot about the health of the ecosystem. If there’s a sudden decrease, this could indicate that there are ecosystem problems, while a sudden increase tells us that the environment is healthy and thriving.
Physical Adaptations of Arboreal Frogs
In order to thrive in their arboreal habitat, tree frogs have several physical adaptations. This includes some of the things I have already touched upon in my introduction, such as padded feet for grip and camouflage as well as things like the ability to breathe through their skin!
Camouflage to Blend in
Tree frogs have the benefit of living among dense foliage which helps to conceal them. But they do go one step further and have some unique colorations to help with camouflage. Some have colors that are very similar to the leaves, while others are patterned to ensure they blend into the bark and other environmental textures. Over time, different species have evolved camouflage traits according to their environment and, it’s been shown that natural selection has favored frogs whose camouflage is more effective. There are even some species of tree frogs that are able to change their colors and patterns to ensure they consistently blend in. One example of this is the Japanese tree frog. In studies it was able to adjust its dorsal patterns according to the pattern and color it was placed on.
The main benefit of camouflage is that the tree frog is better able to evade predators and this ensures its survival. And they don’t do this by halves; tree frogs have an ability known as cryptic coloration, which means they blend seamlessly into their surroundings. When you’re looking for tree frogs, you’ll certainly have your work cut out for you.
The glass tree frog, found in South and Central America has translucent skin on its legs and underbelly. It took scientists some time to figure out why this is, but they’ve finally determined that, when the frog sits with its legs around its body, the translucency makes it blend in better with the leaf.
Each species of tree frog has its own camouflage abilities. For example, one of the most famous is the green tree frog (Hyla cinerea), whose bright green color allows it to blend in with the leaves. There’s also the Amazon milk frog (Trachycephalus resinfictrix), which has colors and patterns along its legs and sides that mimic toxic insects; that’ll certainly put predators off!
Since tree frogs spend a lot of time sitting in the trees, having a mottled brown or green coloration helps them to blend in. This is a trait we see in Wallace’s flying tree frog (Rhacophorus nigropalmatus) which blends in so well, it’s almost impossible to spot.
The mossy frog (Theloderma corticale), so named for its love of hiding among moss-covered structures, has a rough textured skin that’s green in color, allowing it to perfectly blend in with its surroundings.
Limb Structure to Aid Climbing & Leaping
If a creature is going to live in the trees then it needs to be able to move around without falling. That’s where the tree frog’s toe pads come in. Not only are these rounded discs designed to give a wider surface area but they also secrete a special mucus which fills the gap between the substrate and the pad, allowing them to grip onto surfaces of varying textures.
Scientists have likened the adhesion of the toe pads to the surface to wet tissue on glass. So, one would assume that it would be tricky to peel the toe pads away. But amazingly, these frogs are able to do this with ease by rotating the angle of their feet which in turn, increases or decreases the effectiveness of the adhesion. So, they can quickly tear themselves off a surface when required, but thanks to Van der Waals forces (the concept of attraction and repulsion between atoms*), they’re also able to stick to smooth vertical surfaces without using up a lot of energy. (*source)
The adaptations of the tree frog’s feet don’t end there; many species, like the waxy monkey tree frog, have prehensile hands and feet that allow them to grasp twigs and branches with ease and stability. They often have elongated hind limbs as well which ensure flexibility when moving among the trees.
Being able to grasp branches and move effectively is one thing, but tree frogs also need to jump between structures, and they’re able to do this thanks to those long hind legs which are equipped with powerful muscles that propel the frog forward. In some cases, tree frogs are known to jump up to 50 times their own body length.
Respiratory Adaptations for Humid Environments
Since arboreal frogs may not have as immediate access to water as their terrestrial counterparts, they need to be able to retain moisture. Many species do this by absorbing moisture through their permeable skin from the environment. Living in tropical regions, the air is often humid, and this helps to keep them hydrated. What’s more, in these humid conditions, the frog is also able to exchange gasses through its skin in a process known as cutaneous respiration; essentially, they breathe through their skin, even though they still have lungs.
This is essential because there is a greater risk of lower oxygen levels in a humid environment. Through the use of cutaneous respiration, the frog is less likely to suffer the effects of a lack of oxygen. What’s even more fascinating is that these frogs are able to adjust their rate of respiration depending on the availability of oxygen in a process called metabolic flexibility.
Of course, retaining water in their skin is one thing, but there’s always the risk of evaporation. However, some species of tree frogs are able to secrete a special substance that coats their skin and helps to reduce the risk of evaporative water loss. While they’re often found in humid environments, there is still a risk of dry spells which could cause the frog to become desiccated, this aforementioned ability ensures that this doesn’t happen.
Behavioral Adaptations of Arboreal Frogs
As well as the fascinating physical adaptations of tree frogs, these amazing creatures have also evolved certain behaviors that ensure their survival.
Tree frogs come in a range of sizes from less than a few inches to a whopping 5.5 inches (14 cm) (the white-lipped tree frog). Even so, they’re pretty small and therefore vulnerable to predation. But by being most active at night, tree frogs are better able to keep out of the way of predators and also avoid human interactions.
Additionally, hunting and foraging at night means that tree frogs are afforded greater concealment, despite the fact that they have some interesting colors and patterns that aid in camouflage.
What’s more, the areas in which tree frogs live are often very hot so keeping their activity to the hours of darkness, they’re better able to avoid these extreme temperatures. Moreover, these tropical environments are usually more humid at night time which is ideal in ensuring the frog retains its moisture.
The diet of tree frogs may vary by species but by and large, they are insectivores. Smaller species may favor flies, while larger tree frogs might feed on crickets or locusts. In any case, insect activity is often greater at night which improves their hunting success. That said, there are some species whose evolutionary adaptations mean they hunt at dawn and dusk, making them crepuscular, such as the gray tree frog.
All animals need to communicate with one another for things like mating, alerting each other to danger, and defending their territory. Tree frogs are no exception and they have a range of distinct calls and vocalizations that allow them to do this. These sounds vary between species in terms of pattern, duration, intensity, and even frequency which allows each species to differentiate between calls from others of the same species and different types of tree frogs. Think of it in the same way that we use languages.
As I mentioned earlier, male tree frogs are known for their nocturnal vocalizations, which are used to attract a mate. What’s more, it appears they’ve adapted this way in order to make calls without attracting attention from predators.
Each frog has his own pattern of calls, allowing females to choose a mate from the many potential suitors. Often times, several tree frogs can be heard in chorus which helps to enhance the effectiveness of their calls. Amazingly, females are able to pick out the sounds of any given individual male.
In addition to mating calls, tree frogs exhibit calls that help them establish their territory as well as defending it against invaders. This is again something that’s often seen among male frogs.
Although the type of call you might hear will vary depending on what the frog is trying to convey. For example, the mating call will be different from that of an aggressive frog. The red tree frog not only uses sounds to communicate but also sends vibrations through the foliage as a form of enhanced communication.
Some frogs, such as the tree hole frog of Malaysia, will even adjust its pitch to produce echoes that increase vibrations and make their calls louder and more effective when looking for a mate. That said, many frogs have vocal sacs that are designed for amplification.
Nesting & Reproduction
In order to make the most of their arboreal environment, tree frogs have developed several adaptations to their nesting and reproductive habits. They usually choose nests in locations that offer the best protection to their eggs and young and that have good levels of humidity.
Different species have developed different nesting strategies based on their environment. One interesting example of this are the canopy pools used by species like the broad-snout casque-headed tree frog. The nests are created by the frogs, usually among plants from the Bromeliaceae family and are temporary pools of water that protect the eggs from predation, high up in the canopy.
Males and females may even mate within canopy pools after the male makes his initial courtship vocalizations. After this, the parents will carefully tend to their eggs, controlling the temperature within the nest and keeping them safe from predators. Once the eggs hatch, some species, such as the Cuban tree frog, will transfer the tadpoles to a body of water to ensure they do not become desiccated. In any case, nest sites are chosen based on moisture and humidity levels as well as other factors like tree cover and temperature.
Another great example of nesting strategies are the phytotelmata nests, which are water nests created in foliage cavities. These are ideal for not only holding eggs but also provide a safe environment for the newly hatched tadpoles. Pitcher plants are often used because of their ready-made structures.
Arboreal Frog Species
With more than 800 species of tree frogs in the world, it would be impossible for me to detail all of them. However, I’d like to take a closer look at some of the most fascinating species and their unique adaptations and behaviors.
1. Gray Tree Frog (Dryophytes versicolor)
The gray tree frog belongs to the Dryophytes family and is found in various locations around North America, notably from the eastern US up to southeastern Canada. These frogs feed on a diet of insects, primarily spiders, mites, and snails. However, as tadpoles, gray tree frogs eat algae.
Found in both wild and urban habitats, the gray tree frog is commonly spotted in gardens and is drawn to artificial light because of the insects it attracts. In the wild, they inhabit swamps, woodlands and forests where the males can be heard making trilling sounds to attract a mate.
During the breeding season, females lay their eggs on the underside of vegetation over a body of water so that the tadpoles are directly deposited into the water upon hatching. In order to cling to the foliage, gray tree frogs have sticky toe pads that also help them when climbing.
These frogs are masters of disguise with green to gray textured skin that aids them in camouflage. Typically they grow to around 1-2 inches (2.5-5 cm) and are able to change color to adapt to their surroundings. Spotting a camouflaged gray tree frog is pretty difficult as they blend right in, keeping them safe from predators.
2. California Tree Frog (Pseudacris cadaverina)
From the Pseudacris genus, the California tree frog is often found in coastal woodlands and grasslands. They’re native to the western parts of North America and are a small species that doesn’t typically grow to more than 1.5 inches (3.8 cm). Owing to the often warm climates where they live, California tree frogs may enter a state of aestivation in hot spells which they do in a cool, moist spot.
In terms of coloration, California tree frogs perfectly match their surroundings in shades of brown and green. They’re also able to adjust their colors to suit their habitat and conceal them from predators. Some say this species looks like a granite stone because of its unique coloration.
Like many tree frog species, the California tree frog has sticky toe pads that help it climb and cling to the vegetation. This comes in handy when hunting for spiders, beetles, and ants, which they do at night.
California tree frogs have a classic ‘ribbit’ call which is very loud and used to attract a mate. After eggs are laid, it can take between 40 and 75 days for the tadpoles to undergo their metamorphosis and become adults.
3. European Tree Frog (Hyla arborea)
The European tree frog is a member of the Hyla genus and enjoys a variety of habitats, including grasslands, forests, and wetlands. It has an impressive range that stretches all the way from Europe to western Asia, thanks to its tolerance of various climates, where it feeds on an insectivorous diet. As they consume so many insects, they’re important within their habitats to control their prey species’ populations.
With a bright green coloration, the European tree frog is easily able to blend in with foliage and moves through it thanks to adhesive toe pads. Unlike a lot of tree frog species, this one doesn’t always live in an arboreal environment.
European tree frogs are a small species that grows to no more than an 1.5 inches (3.8 cm) in length. They make a unique ‘reep reep’ call, primarily in the breeding season, which occurs in the warmer months.
4. Red-Eyed Tree Frog (Agalychnis callidryas)
The red-eyed tree frog is part of the Agalychnis genus and is a mid-sized species that grows to around 2-3 inches (5-7.6 cm). They’re one of the most interesting looking tree frogs with, as their name suggests, bright red eyes on a green body. Those red eyes are a deterrent for predators, but they’re also used for communication. These frogs are also known for their markings, which come in blue and yellow.
So iconic is the red-eyed tree frog that it’s often used as a symbol for biodiversity in the tropical rainforests it inhabits in Central America. Here, these frogs feed on a diet of spiders, crickets, moths, and other insects which they hunt for at night. They’re known for their loud calls during the rainy season when breeding takes place. Conveniently, the females lay their eggs on the underside of leaves, allowing the tadpoles to fall into the water below when they hatch.
As well as having adhesive toe pads for climbing, red-eyed tree frogs have extremely powerful muscles in their hind legs that allow them to jump between branches. In the canopy, you might think they stand out like a sore thumb, but you’d be surprised how well their green bodies allow them to blend in.
5. Squirrel Tree Frog (Hyla squirella)
The squirrel tree frog is a member of the Hyla genus and is found in the southeastern parts of the United States, where it inhabits various habitats. Not only forests but also marshes, swamps, and even domestic gardens.
You might wonder where this species gets its name, and it’s because of the calls it makes that resemble those of a squirrel. The males make these calls during mating season to attract females.
These small frogs that grow to around 1.5 inches (3.8 cm), feed on an insectivorous diet of spiders, beetles, and ants. They’re known for their ability to control insect populations within their habitats, where they also have color changing abilities which help them to blend in. Generally speaking, squirrel tree frogs range between green, gray, red, and brown.
Like many tree frog species, the squirrel tree frog has sticky toes pads that assist it when moving through its environment. However, one of their unique abilities is being able to tolerate a lack of moisture much better than other tree frogs. Even when partially dehydrated, they’re able to survive and can tolerate up to a 34% loss of water weight before becoming desiccated.
6. Gliding Tree Frog (Agalychnis spurrelli)
The gliding tree frog is found in lowland rainforest habitats in Central America, where it lives in the tree canopy. As the name suggests, this species is able to glide between trees at a distance of up to 40 to 50 feet (12 to 15 meters). This is thanks to special skin flaps, and the behavior allows them to evade predators.
Gliding tree frogs are insectivores and can grow to around 2 inches (5 cm) as an adult. Tadpoles are born in the rainy season, and females lay their eggs so that the newly hatched young can fall straight into the water.
Sometimes, this species is called the flying frog, although it’s important to remember that they do not actually fly, but glide. That said, their special skin flaps allow them some impressive control over their descent.
7. Australian Green Tree Frog (Litoria caerulea)
Part of the Litoria genus, the Australian green tree frog is a large species that can grow up to 4 inches (10 cm) in length. They’re found all over Australia in various habitats, including wetlands, rainforests, and coastal areas. Sometimes, they’re even found in domestic gardens where they go on the hunt for insects and invertebrates.
Australian green tree frogs have a bright green coloration which is ideal for concealing them among the leaves. In its arboreal habitat, this species, like many others, has sticky toe pads which aid in climbing and stability.
During breeding season, the iconic ‘wark wark’ call of the Australian green tree frog can often be heard. There’s usually a good number of these frogs, and their presence is used to indicate the health of their ecosystem.
Tree frogs are a popular exotic pet, and the Australian green tree frog is one of the more commonly adopted species. This is largely due to their beautiful appearance but also because of how easy they are to care for.
8. Lemur Leaf Frog (Agalychnis lemur)
The lemur leaf frog is found in Central America and typically inhabits rainforests at both low elevations and in montane regions. These are small frogs that grow to around 1.2-1.6 inches (3-4.1 cm) and feed on an insect based diet consisting of flies, moths, and crickets.
Lemur leaf frogs are well known for their stunning appearance that resembles that of a lemur owing to their sizable eyes. This is where the frog takes its name. They have a bright green coloration that helps it to blend into the foliage and subtle black spotted markings over the back.
The benefit of having such large eyes is that the lemur leaf frog is able to better detect the movement of incoming predators like birds and lizards. With vertical pupils, these frogs are also able to see well in the dark. Another interesting adaptation is the lemur leaf frog’s urine, which it uses to cover its body in an attempt to remain moist.
While the lemur leaf frog is a small species, it certainly makes up for its size with its loud call. These frogs make a whistling sound. During breeding season, males make a series of clicking sounds to attract a female. Sadly, this species, while interesting, is considered to be critically endangered.
9. Giant Monkey Frog (Phyllomedusa bicolor)
From the Phyllomedusa genus, the giant monkey frog is found in South America, primarily in the Amazon rainforest. Here, these frogs, that can grow up to 5 inches (12.7 cm), hunt for insects like moths and crickets.
These frogs have a bright green body with a creamy colored underbelly and have significantly large toe pads that allow them to move through the foliage and cling to surfaces. While its coloration provides some camouflage, it serves more as a warning to predators of the frog’s toxicity. The toxic secretions, called frog glue, contain opiates and peptides that are often used in traditional cleansing ceremonies to induce vomiting.
Giant monkey frogs have distinct black and white eyes and orange markings on the body. This appearance as well as its cultural significance make it one of the most talked about and admired tree frog species.
10. Waxy Monkey Frog (Phyllomedusa sauvagii)
The waxy monkey frog takes its name from two of its most unique characteristics. These frogs secrete a special wax from their skin, which allows them to remain in the sun for prolonged periods without drying out. Additionally, this coating protects the frog against contaminants and predators. What’s more, rather than jumping through the trees, this species, from the Phyllomedusa genus, walks just like a monkey.
Interestingly, this South American species is one of the lesser-known tree frogs and this is largely because of its ability to adapt to a range of habitats. That said, it’s most commonly found in rainforests where it lives on a diet of insects.
Waxy monkey tree frogs can be seen among the leaves and on branches where they blend in thanks to their green to brown coloration. They grow to around 2.5 inches (6.4 cm) maximum and have a loud call described as an ‘aaak’ sound, which males use to attract females during the rainy season when breeding occurs.
11. Spring Peeper (Pseudacris crucifer)
Found in North America, the spring peeper is a species from the Pseudacris genus that feeds on a diet of insects and can grow to around 1.25 inches (3.2 cm) in length. These tree frogs have a unique appearance with a slender body and a dark marking that looks like a cross on the back. Their main body color ranges from light brown to tan, and they’re found in woodlands and wetlands as well as domestic gardens in suburban areas.
The spring peeper might not be the most colorful of the tree frogs but it does have a very distinct call which sounds like ‘peep peep’; no prizes for guessing how it got its name. Moreover, this call is typically heard during the spring time when males come together at breeding sites and make a chorus to attract females.
As is the case with most tree frogs, spring peepers have sticky toe pads that allow them to climb and adhere to surfaces. Another unique adaptation is their ability to produce special compounds that prevent them from freezing during cold weather. This is thanks to the way that sugars are concentrated within the frog’s cells.
12. White-Lipped Tree Frog (Nyctimystes infrafrenatus)
Named for the white linear marking along the mouth, the white lipped tree frog, part of the Nyctimystes genus, is the largest species of tree frog. It grows to around 5 inches (12.7 cm) in length and has a marbled pattern in colors of brown, green, and cream.
The white-lipped tree frog, sometimes called the giant tree frog is native to Australia, where it lives in moist habitats like wetlands and rainforests. Here, it hunts for insects as well as invertebrates, such as worms.
Being a larger species, you might think that the white-lipped tree frog is not as agile, but it’s an excellent climber and is equipped with sticky toe pads. They spend a lot of their lives among the trees, where their coloration helps them to blend in.
Breeding takes place in the rainy season, and male white-lipped tree frogs have a vocal sac called the infrafrenata, which allows them to make a loud sound similar to a dog barking in order to attract a mate. When distressed, these frogs may also make a mewing sound, similar to a cat.
13. Cope’s Gray Tree Frog (Dryophytes chrysoscelis)
Cope’s gray tree frog is found in the United States and Canada and has a unique textured appearance with a gray to green coloration. This helps it to camouflage, but the species is also able to change color to suit its environment. The hormones that control this ability also enable the frog to regulate its body temperature.
From the Hylidae family, Cope’s gray tree frogs prefer a forest habitat but are also sometimes found in urban areas. They grow to around an 1.5 inches (3.8 cm) in length and, like most species, have sticky toe pads.
The Cope’s gray tree frog is often misidentified with the gray tree frog as their appearances are strikingly similar. However, the two can be differentiated by their mating calls. That of Cope’s gray tree frogs occurs in two parts and has a trilling sound. This can commonly be heard in the warm season during the evenings.
14. Wallace’s Flying Frog (Rhacophorus nigropalmatus)
Wallace’s flying tree frog is an interesting species that is found in southeast Asia where it primarily lives in rainforests close to a water source. As their name suggests, these frogs are able to glide between the trees thanks to their webbed feet. Amazingly, they’re able to travel up to 50 feet (15.2 meters) at a time! When you consider that they only grow to around 4 inches (10.2 cm), that’s pretty impressive.
These frogs are usually green to brown in color, which aids in concealing them from predators. Most active at night, Wallace’s flying tree frogs come out to hunt for insects and invertebrates.
Their webbed fingers and toes contribute to their unique appearance as well as their large eyes and long limbs which also aid in jumping and climbing. These adaptations are perfect examples of how different tree frog species have evolved to suit their environments.
In terms of breeding, the courtship rituals of Wallace’s tree frog is very similar to other species, with males emitting a loud call to attract a female. The eggs are laid underneath a leaf, allowing the tadpoles to directly enter the water once they’re born. Before hatching, the eggs are contained in a bubble which is produced by secretions from the female, and she can lay up to 400 eggs in a single clutch!
15. Dainty Green Tree Frog (Ranoidea gracilenta)
The dainty green tree frog is sometimes called the graceful tree frog and is a species from the Ranoidea genus and inhabits rainforests and woodlands in the northeastern part of Australia, primarily Queensland. However, this species is not afraid of humans and will often enter gardens and even houses in search of food.
Dainty green tree frogs, despite their name, grow to around 1.8 inches (4.6 cm) in length and have a green upper body with a cream to white underbelly. They can be characterized by the white markings near the eyes.
Breeding in the rainy season, dainty green tree frogs are often abundant during floods, and males can be heard in chorus, trying to attract a mate. When females lay their eggs, they’re contained in a jelly sac, which she attaches to the underside of a leaf, ready for the tadpoles to drop into the water below once they hatch.
Challenges & Threats Facing Tree Frogs
Sadly, many tree frog species face threats from humans and environmental factors such as habitat loss, pollution, and the effects of climate change, among other things. Fortunately, conservationists are aware of these problems, and there are several efforts in place to protect these wonderful animals.
A problem for a lot of animals is habitat destruction, and tree frogs are no exception. It’s believed that around 32.1 million acres (13 million hectares) of forests are destroyed each year, and this is important habitat for these creatures, putting many species at risk, including up to 17% of species in the Amazon alone. In Brazil’s Atlantic forest, as much as 90% of the habitat has been lost which is devastating news since this is considered a biodiversity hotspot and home to rare species like the golden poison dart tree frog. Moreover, the Amazon is one of the most threatened areas on the planet yet it is home to iconic species like the red-eyed tree frog.
Humans are creating more and more urban areas and encroaching on tree frog habitat, with this reach expected to triple by the year 2030. And it’s not just urbanization that’s a problem. Humans are also expanding their agricultural land, especially in Southeast Asia where palm oil plantations are taking over tree frog habitats and, as a result, affecting their numbers.
Not only does this human activity reduce the current populations, but it also has an impact on the frogs’ ability to breed as nesting sites are also destroyed. As more areas are destroyed, the food availability for tree frogs becomes sparser, further affecting their populations.
Another problem with habitat destruction is that it impacts the climate of the forests that these frogs call home. Around the borders of the forests that are being taken away, more sunlight is able to penetrate causing the temperature to go up. This affects the microclimates within the forest and further limits the available space for frogs. This is known as the edge effect.
Mining is another issue that’s causing a loss of tree frog habitat, especially in places like the Western Ghats in India, where mining is impacting the ecosystem and resulting in habitat destruction for tree frogs and other species. It’s thought that there are around 200 amphibian species here with new ones being constantly discovered, including the galaxy tree frog. Despite conservation efforts being in place in this UNESCO World Heritage Site, the Western Ghats is losing tree cover which is having a direct impact on frog populations. What’s more, up to 90% of the species are endemic and are therefore more sensitive to even the smallest changes.
If that wasn’t enough, all of this new infrastructure needs to be accessible to humans, so more roads are being built. As frogs try to move between habitats, many are becoming the victims of traffic.
This may not be such an issue if habitats were not fragmented, which is just as much of a problem as habitat destruction. Fragmentation means that frogs are segregated to limited areas and may not have access to as much food, shelter, or even potential mates. This is something we are seeing more and more frequently in the forests of Borneo. However, since this is an incredibly biodiverse area with around 155 species of tree frogs, conservation efforts are in place to prevent further fragmentation and protect frog populations.
Some species are endemic to islands and these are among the most vulnerable. For example, on the Caribbean island of Puerto Rico, the Monteverde’s harlequin frog faces significant problems not only because of habitat loss but also the chytrid fungus which limits the frog’s ability to produce keratin.
Thankfully, there are many programs in place that aim to restore lost habitat as well as efforts to encourage more sustainable use of the land by humans, allowing nature and people to live side by side. For example, the Rainforest Trust is working to protect frog habitat all over Latin America, Asia, and Africa. Moreover, organizations like Save The Frogs are offering ecotourism to raise awareness and regularly hold events to educate people on the importance of protecting habitats.
Most of us are aware of the devastating effects that climate change is having on the planet. The rise in global temperatures is happening so quickly that it’s estimated that, on average, the temperature is now 2.2°F higher than it was at the end of the 19th century. The problem for tree frogs is that they require specific temperatures to thrive, and even the slightest shift can throw them out of whack because of their ectothermic physiology. When temperatures change just a little, this has a direct impact on their breeding, metabolism, and other behaviors.
In terms of breeding, temperature changes can alter when the frogs mate. For example, the boreal chorus frog and the red-eyed tree frog have been noted to start breeding earlier because of how warm the temperatures are in early spring. The problem with premature breeding is that there may not be enough resources to sustain the mothers and their young. Moreover, studies have shown that higher temperatures can speed up the development of tadpoles, which means individuals are not as strong once they reach adulthood. And if that wasn’t enough, consider that climate change is responsible for altering the mating calls that allow adult males to find a mate.
While all tree frog species are somewhat sensitive to temperature changes, there are some that are more vulnerable than others. For example, the golden toad has now been listed as extinct as a result of the effects of climate change. Earlier I talked about the chytrid fungus which affects tree frogs, and its growth and spread is exacerbated with rising temperatures. Interestingly, Asian frogs appear to be resistant to the fungus, while those in the Americas are fighting for their lives against it. However, organizations from around the world have come together in an effort to protect these vulnerable animals.
Not only are things heating up but climate change is causing longer periods of drought and unpredictable precipitation patterns. Since tree frogs rely on moisture, this is an obvious problem not only to the survival of individuals but also for their breeding since tadpoles require water to live in as they undergo metamorphosis. In America, the green tree frog is known to struggle finding suitable breeding sites for this very reason.
In order to escape these changes, many tree frog species are moving to higher elevations where temperatures are lower. However, this doesn’t take away from the fact that climate change also has an impact on tree and plant life, which doesn’t help when it comes to habitat loss. In Hong Kong, scientists are looking at reintroducing wildlife into the forests in order to restore habitat through things like seed dispersal. This cannot come quickly enough as come frog species, like the Romer’s tree frog have already completely lost their habitat here. That said, reports still show that climate change could be up to 4.5 times more likely to destroy tree frog populations than habitat destruction, so it’s something that we need to pay attention to.
When most people think of pollution they imagine chemicals and plastic waste. While these do pose an issue to tree frogs, things like light and noise pollution are also causing major problems. What’s more, humans are allowing up to 80% of untreated wastewater to be released into the environment, much of which heads directly to frog breeding grounds. When this happens, the pollutants, such as chemical runoff from agriculture, can hinder the development and survival of tadpoles.
Even adult frogs are impacted by these chemicals. Most notably, substances containing neonicotinoids and atrazine are known to affect the hormonal systems of the frogs which negatively impacts their ability to reproduce successfully. And it’s not just in the water; these chemicals are being absorbed into the soil and this includes contaminants like heavy metals. These metals have been found at worrying levels in the bodies of tree frogs that live near urban areas.
Not only this, but when these contaminants are found in the environment, they affect all levels of the food chain and so are passed between species. There are also microplastics in the water which can be ingested by the tree frogs. Since they contain toxic chemicals they can cause physiological damage or even death. Even if death doesn’t occur, these toxic chemicals can cause deformities and research shows that, in some regions, as many as half of all frogs are suffering from these effects. Still, in studies, around 90% of frogs were found to have ingested some level of microplastics.
Moreover, where frogs have been affected by pollution, their immune systems may be compromised, making them more susceptible to other problems like the chytrid fungus.
As I mentioned earlier, light and noise pollution are significant factors in frog survival. Did you know that the noise from traffic can interfere with the mating calls of tree frogs? When traffic noise is high, frogs have to expend more energy to emit their calls which impacts their overall fitness. What’s more, the effectiveness of mating calls has been reported to be diminished in tree frogs that live in urban areas. Light is also an issue and in urban areas, this has been shown to affect various behaviors in tree frogs and ultimately impacts their level of activity. This is particularly true when it comes to breeding and feeding. Yet, the presence of artificial light remains a problem. Studies have shown that light at night causes frogs to become more susceptible to other stressors.
The chytrid fungus, which I have mentioned several times in this article, causes a disease known as chytridiomycosis and this is responsible for the deaths of tree frogs all over the world. So intense are the effects that it’s reported that this disease has caused the greatest ever loss of biodiversity, affecting as many as 500 species, 90 of which have now been made extinct.
The southern corroboree frog of Australia is reported to have declined in number by a whopping 90%. This is likely due to the fact that climate change causes the frogs’ immune systems to weaken, making them more susceptible to chytridiomycosis.
Ranavirus is another disease that affects amphibians, including tree frogs and affects frog species all over the world. For example, in the United Kingdom, an outbreak of the disease led to a worrying decline in the number of common frogs. This species, along with the common toad are said to be particularly vulnerable to the condition.
But the problems aren’t just the diseases themselves but how easily they can spread. Many viruses and fungi can be transmitted through water as well as direct contact between individuals. Moreover, we have to consider that tree frogs are commonly transported around the world for the pet trade, or even accidentally in shipments. Infected individuals are then easily able to pass on diseases as they travel. Disease strains are also constantly being discovered, such as a new strain of the chytrid fungus.
Owing to the number of other threats to tree frogs, many are under great stress. When the frogs are stressed, this weakens their immune systems making them more vulnerable to disease. Scientists report that detecting disease in their early stages is vital, but implementing this early detection is incredibly challenging because symptoms are not always obvious.
Still, conservation efforts are still in place in an attempt to limit the spread of disease. One such example is the captive breeding of frogs that are then reintroduced to the wild. Not only are these captive-breed frogs stronger, but they’re also able to repopulate areas where numbers have declined because of other factors like wildfires. These programs have shown promising success. For example, the Wyoming toad was reintroduced to the wild and numbers soared from just 10 individuals to more than 1500.
Not only this, but conservationists are working on the wider environment, aware that the overall health of everything in it, including humans and animals has an impact on individual species. This is known as the One Health Approach and is a collaborative approach that focuses on how the health of all species is interconnected. By looking after them all, we improve biodiversity and the resilience of an ecosystem to things like disease.