Gray Treefrogs’ Self-cleaning Toe Pads
Scientists have discovered that the angle of the toe pads and a secretion of mucus are involved in a treefrog’s ability to stick to wet, smooth leaves, rough, dry trees and other surfaces. They also allow the toes to “self-clean.”
To make their feet sticky treefrogs secrete mucus. They increase their adhesion by moving their feet against the surface of what they are clinging to in order to create friction. As a frog moves across a surface, its feet accumulate dirt, which impedes its ability to stick to the surface it’s walking on. Scientists have discovered that the mucus combined with this friction-creating movement not only allows the frog to adhere to the surface but simultaneously rids their feet of accumulated dirt and debris as they walk.
This remarkable adaptation may provide a design for self-cleaning sticky surfaces, which could be useful for a wide range of products, especially in contaminating environments such as medical bandages and long-lasting adhesives. (Thanks to Janice Perry for photo opportunity.)
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An Unexpectedly Early Juvenile Gray Treefrog
At this time of year the bird-like courtship trills of male Gray Treefrogs can be heard throughout the night from shrubbery bordering wetlands. Mating is taking place, eggs are being laid and typically the offspring would be seen in July and August.
Imagine my surprise when I discovered this 3/4″ juvenile Gray Treefrog recently. It’s possible that it could be this year’s — eggs take 2-5 days to hatch and tadpoles metamorphose into adults in 30-60 days. Early-emerging treefrogs could have parented this individual. But it’s also possible that it could have overwintered as a juvenile. While we’ll never know its exact age, it’s fun to see a juvenile this early in the season.
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Northern Leopard Frogs Emerging From Hibernation And Males Are Starting To “Snore”
Spring Peepers, Wood Frogs and a variety of salamanders steal the early bird show when it comes to amphibians, but now other species are beginning to appear, including Northern Leopard Frogs which are emerging from the mud at the bottom of the ponds, marshes and streams where they spent the winter. These frogs migrate to their breeding grounds soon after becoming active and before long the males’ sonorous courtship calls will be heard.
During the breeding season males advertise on land and in the water for females with a hoarse snore-like croak followed by two or more clucks. A chorus of them can be fairly deafening. Both males and females also give aggressive calls, males when grasped by another male and females when grasped by a male after they have finished laying their eggs.
To hear a male Northern Leopard Frog’s mating call, go to https://musicofnature.com/calls-of-frogs-and-toads-of-the-northeast/ and scroll down. It’s as distinctive as the Spring Peeper’s “peep” or the Wood Frog’s “quack.”
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Amphibians On The Move
According to Jim Andrews, Director of the Vermont Reptile and Amphibian Atlas Project (https://www.vtherpatlas.org), the recent warm rain triggered a significant movement of many amphibians in the Lake Champlain Basin as they left their hibernation sites and migrated towards their breeding grounds. Blue-spotted Salamanders (& hybrids), Four-toed Salamanders, Spotted Salamanders, Eastern Red-backed Salamanders, Eastern Newts, Spring Peepers and Wood Frogs were among those seen emerging from their hibernacula.
Keep your eyes peeled on warm (40°+), rainy evenings and see if you discover a popular amphibian road- crossing location. Check local resources to see if there is a local volunteer group that assists these slow-moving migrants across the road. If not, you could start one yourself – be sure to wear reflective clothing, have a flashlight and report your findings to a local nature center or conservation organization. (Photo: Blue-spotted Salamander by Erin Talmage)
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Northern Leopard Frogs Migrating
Northern Leopard Frogs (Lithobates pipiens) are often found in wet, grassy meadows where they spend the summer after breeding in a body of water. Come fall, they typically migrate towards the shoreline of a pond, traveling up to two miles in order to do so.
Northern Leopard Frogs cannot tolerate freezing temperatures, so as it begins cooling off in October and November, these irregularly-spotted amphibians seek protection by entering the water and spending the winter months hibernating on the bottom of the pond. They are sometimes covered with a thin layer of silt, sometimes not. Usually they clear the area either side of themselves in order to facilitate respiration. Movement, if there is any, is very slow.
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Wood Frogs Laying Eggs
Have you ever wondered how grapefruit (and larger)-size masses of up to 2,000 eggs come out of a 2- to 3-inch-long Wood Frog that weighs about a third of an ounce? It turns out that a Wood Frog’s eggs are highly compressed into a mass the size of a golf ball when laid! In under an hour they have absorbed enough water to have expanded to the size we usually associate with Wood Frog egg masses. (Photo: three freshly-laid (darker) egg masses amongst older egg masses)
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Male Wood Frogs Calling
Usually it’s your ears that tell you that Wood Frogs (Lithobates sylvaticus) have emerged from hibernation. They are one of the first amphibians to announce themselves, often appearing before snow and ice are completely gone. Male frogs congregate in shallow ponds and vernal pools, where their ardent courtship ensues.
Unlike most frogs, which have a single vocal sac below their mouth, Wood Frogs have two paired sacs, called paired lateral vocal sacs, located on either side of their body just behind their head (see photo). With their mouth and nostrils are closed, male frogs pump air back and forth from their lungs to their inflated vocal sacs which vibrates their larynx and produces a duck-like quacking sound. The vocal sacs act as resonating chambers, amplifying the frogs’ calls so as to attract females from far and wide.
Vocal sacs serve a dual purpose for some frogs. As soon as the eggs of Darwin’s Frog (Rhinoderma darwinii), found in Chile and Argentina, hatch, the male scoops the tadpoles into his mouth and they spend the next six weeks metamorphosing inside his vocal sac. The male does not eat until the tadpoles have matured into adults and exited his mouth.
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American Toads Preparing For Winter
In the Northeast, sometime in September or October you realize that you’re no longer seeing American Toads. This is because they are taking steps that allow them to survive over the winter. These steps consist of either finding another animal’s burrow or digging their own (up to 20 inches or so deep) in order to hibernate below the frost line.
As the photograph illustrates, toads dig their tunnels facing forward, using their hind legs to do the digging. Special hardened knobs on their hind feet assist them in this endeavor. As they dig deeper, the tunnel in front of them collapses. When deep enough to hopefully avoid being frozen, they stop digging and hibernate until the soil begins to warm. Come April or May, American Toads dig their way up to the surface of the ground and head for breeding ponds. (Photo by Ashley Wolff)
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Spring Peepers Peeping
The peeps of male Spring Peepers can be heard fairly consistently this time of year. Unlike in the spring, these calls are coming not from bodies of water, but from the woods nearby. And they are single peeps coming from individual peepers, not the chorus of “sleigh bells” one hears in the spring. This phenomenon occurs so regularly in the fall that herpetologists have given it a name – “fall echo.” They speculate that the calling of peepers is spurred by light and temperature conditions that mimic those that occur in the spring, during Spring Peeper mating season.
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Gray Treefrogs Metamorphosing
Gray Treefrogs are often heard but rarely seen, due both to their cryptic coloration as well as the fact that they are arboreal. They tend to perch (grasping trees with their toes which bear large, adhesive, mucous-secreting disks at their tips) in vegetation surrounding swamps and ponds, where their robust, territorial and mating trilling can be heard (males call between 500-15,000 times per hour). To hear trilling Gray Treefrogs go to https://www.youtube.com/watch?v=CSkhM24Fi-k.
After choosing a mate and mating, Gray Treefrog females lay up to 2,000 eggs which hatch in 2-5 days. For the next month or two the tadpoles breath with gills and consume vegetation. Full-sized tadpoles are green or black with red or orange tails. Towards the end of summer, the tadpoles begin their transformation into frogs, developing limbs and lungs, absorbing their tails and changing from a diet of plants to one of insects.
Adult Gray Treefrogs are mottled gray or green (depending on their surroundings, temperature, and humidity) and have an uncanny resemblance to lichen. Recently-metamorphosed young treefrogs such as the one pictured are a brilliant emerald green. (Photo: young Gray Treefrog with adult Gray Treefrog inset) (Thanks to Brian Long for photo op.)
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Tadpole Maturation
The eggs of Wood Frogs, the earliest species of frog to breed in the Northeast, are just hatching and tiny Wood Frog tadpoles can be found swimming about at this time of year. This Green Heron is devouring a tadpole, but it is anything but tiny – certainly not a Wood Frog tadpole. How can this be?
The answer is that the tadpole that the Green Heron caught did not hatch this spring – it hatched last summer. Unlike Wood Frogs and Spring Peepers that mature in roughly two months, Green Frogs and American Bullfrogs can take two or even three years to metamorphose into adult frogs. By their second summer they are of substantial size. The Green Heron has caught a Green Frog or Bullfrog tadpole that has overwintered and would probably have matured this summer.
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Eastern Red-backed Salamanders Still Active
The Eastern Red-backed Salamander is the most abundant terrestrial vertebrate in New England. Unlike many salamanders, it is terrestrial year-round – living, mating, laying eggs, feeding, and hibernating.
Eastern Red-backed Salamanders can occur in two color phases, lead-back and red-back. The lead-back phase salamanders are a consistent gray to black color while the red-back phase is characterized by an orange to red stripe down the length of their body and tail. In both phases, they are distinguishable by their mottled white and black undersides and five toes on their hind feet.
Due to its lack of lungs, this slender salamander must live in damp or moist habitats in order to breath. It is active into late fall, inhabiting rotting logs or living under moist leaf litter, bark, stones, etc. When cold weather really sets in, it will hibernate down to 15 inches in the soil, or in deep leaf litter or rock crevices. (Congratulations to Helen L., the first NC reader to correctly identify the latest Mystery Photo as an Eastern Red-backed Salamander!)
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Male Green Frogs Defending Territories
Male Green Frogs are extremely territorial. During June, July and August they establish a series of territories, often claiming each one for less than one week before moving on.
The desirability of a given territory is of utmost importance – the better the quality (amount of vegetation) of your territory the more likely it is that a female will choose you to fertilize her eggs. The more time a male spends in a high quality territory the greater the number of mates he will acquire.
Considerable aggression is displayed against other males when an individual is claiming and maintaining a territory. When a competing male arrives, a wrestling match often ensues (see photo).
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Big Night!
A magical migration awaits all who take note of the first rainy spring day (in the 40’s) when the rain continues into the night. Last night these conditions resulted in what herpetologists refer to as “Big Night.” While snow still covers parts of the forest, there is ample bare ground that has warmed up enough to waken hibernating frogs and salamanders at this time of year. As if silently communicating with each other, thousands and thousands of these amphibians emerge from their subterranean hibernacula on the very same night and migrate en masse to their ancestral breeding pools, known as vernal pools. They avoid the lethal sun by travelling at night, in the rain. Unfortunately, many die, as they often must cross hazardous roads in order to reach the pool where they breed every year. If you are driving in these conditions, please keep an eye out for these jaywalkers and try to avoid them. Roads can quickly become slick with their squashed bodies.
How many Spring Peepers, Wood Frogs and Spotted Salamanders can you find in this photograph taken on Big Night? (There are six.) Thanks to the unbelievable generosity of Naturally Curious readers, this photograph was taken with my new camera and lens. I cannot tell you how deeply touched I am by your kindness and generosity.
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Young Spring Peepers Appearing
Every year in late July or August a young Spring Peeper crosses my path and I cannot resist photographing it. At this time of year they are roughly the size of a Japanese Beetle, and during early mornings and late afternoons can be found in shrubbery where they intermittently rest in the shade and feed on insects even smaller than themselves. If you live near a pond where it sounded like sleigh bells were ringing last spring, keep an eye out for these irresistible frogs that are no bigger than your tiny finger nail.
Juvenile Gray Treefrogs Appearing
Being my favorite species of frog, the Gray Treefrog may get more than its fair share of exposure on the Naturally Curious blog. This amphibian is rarely noticed outside of its June mating season, when the males’ bird-like trills can be heard throughout the night from shrubbery bordering wetlands. Due to its emerald green coloration when young, and its mottled gray/green adult appearance, in addition to its nocturnal habits, this beguiling amphibian escapes detection by most of us throughout the rest of the summer.
However, if you keep an eye out in August, near where you heard those trills in June, you may be successful in spotting a juvenile Gray Treefrog. Having developed legs and lungs, absorbed their gills and tails, and reinvented their digestive system for insects, not plants, they are now permanently terrestrial, except during the breeding season. When a Gray Treefrog is young and newly metamorphosed, it usually remains near the forest floor. As it ages, it may transition to living in the forest canopy. (Photo: juvenile Gray Treefrog; inset – adult Gray Treefrog)
Gray Treefrogs Well Camouflaged
If there is an amphibian that is a master of disguise, it has to be the Gray Treefrog (Hyla versicolor). This remarkable frog is capable of changing its color (gray, green or brown) to match its environment within half an hour, a process called metachrosis. Shades of gray are most common with black blotches on the back while green colors are more prominent during the breeding season and in yearling frogs.
Being a treefrog, it has large, round, sticky toe pads that help it cling to trees and shrubs, where it spends most of its time. Survival is more likely if predators don’t detect you, so Gray Treefrogs have evolved to look a lot like bark.
When the temperature reaches 59° F. the males’ bird-like trilling can be heard coming from foliage next to and hanging over their shallow breeding pools. If you wish to set eyes on a Gray Treefrog, now is the time, as they are calling and a silent Gray Treefrog can be extremely difficult to find!
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Amphibians Migrating
Vermonters were witness to a record-breaking (early) amphibian migration in the Champlain Valley last week on March 1st, when night temperatures were in the low 50’s. Not only did it occur a week earlier than any other previous major migration, but records show that migration for the earliest amphibians in Vermont is now approximately two to three weeks earlier than it has been during the last decade. (as reported by Jim Andrews, www.VtHerpAtlas.org).
Spotted Salamanders, Four-toed Salamanders, Eastern Red-backed Salamanders, Blue-spotted Salamanders, Jefferson Salamanders, Spring Peepers, Wood Frogs and even an American Toad were on the move. According to Andrews, “this is a concern if the weather turns really cold and the ground and ponds refreeze. If that happens, many of the early migrants (that are not freeze tolerant) could freeze and die. If the weather stays relatively mild, with only short cold snaps, they should be fine.” Weather since these sightings has been unseasonably cold, and one can only hope they survived. (Photo: Spotted Salamander, Ambystoma maculatum)
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Leopard Frogs – Too Little, Too Late
At this time of year one would expect to find Leopard Frogs lying on the bottom of a pond, partially but not completely covered with leaves or mud as they hibernate their way through winter. Because of the depth of a pond, and the fact that in winter the water temperature is around 39°F., ice isn’t an issue at the bottom of a pond, and the frogs and turtles that overwinter there don’t usually freeze.
However, sometimes ponds freeze over before amphibians or reptiles that overwinter in them arrive at their hibernacula. Apparently this is what happened to these Leopard Frogs, and they took refuge in the only open body of water they could find – a large but shallow puddle about 10’ wide by 20’ long in a dirt road. Shortly after they arrived temperatures dropped and the frogs were trapped under (and eventually will be encased in) the ice. Unlike Wood Frogs, Spring Peepers and Gray Treefrogs, Leopard Frogs are not freeze tolerant, so their demise is inevitable. (Thanks to Kelly Maginnis for photo, and Jim Andrews for his herpetological expertise.)
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Fall Amphibian Migration
The migration of amphibians from the woodlands where they overwinter to their breeding pools in March is a familiar spring phenomenon to most. However, some of these amphibians engage in a fall migration as well. Amphibians (and reptiles) need to find a good overwintering spot, where they won’t freeze. In some cases, that might be a few feet upstream or into a seepage area, and in others it is a few hundred yards uphill. The extent of the migration and the species participating vary in different parts of the state.
In western Vermont, Jim Andrews, Director of the Vermont Reptile and Amphibian Atlas(http://vtherpatlas.org), has observed Blue-spotted and Four-toed Salamanders moving down into wetlands in the spring, staying close to the wetland for moisture and feeding during the summer, and then moving uphill back to wintering areas in the fall. On the other hand, he has found that most Spotted and Jefferson Salamanders, as well as Wood Frogs, move down in the spring to breed, and then head back uphill in stages soon after they are done breeding.
Eastern Red-backed Salamanders (pictured) migrate as needed during the summer to maintain their body moisture, and in the fall, search for an animal burrow or crevice to hibernate in. Migration often occurs at night, while it’s raining, so as to prevent their skin from drying out. (Amphibians need to have moist skin because a large portion of the frog’s “breathing” occurs via oxygen diffusing through the skin. Oxygen will not diffuse through a dry membrane.) After the very dry summer we’ve had, a large number of amphibians were observed taking advantage of the recent rain and migrating.
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Gray Treefrog: A Frog of Many Colors
A Gray Treefrog starts life off as a ¼” yellow tadpole. Eventually it may reach 2 ½” in length, and its body will have turned olive green with a red tail. Upon metamorphosing into a frog, the Gray Treefrog turns a bright emerald green and gradually develops into a mottled greenish-gray adult which can change its color from green to gray in about half an hour to match its environment. The two color phases of the maturing frog (solid green of the young, and mottled gray or green of adult) are so different it’s hard to believe that they are the same species. (Photo: young Gray Treefrog; insert- adult Gray Treefrog)
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Spring Peepers Dispersing
If you live near a pond where you heard loud “peeping” in late April or May, now is the time to keep your eyes peeled for young subadult Spring Peepers in the woodlands near the pond, for they are just completing metamorphosis and moving onto land. Thanks to their enlarged toe pads, peepers are good climbers but are usually found on the ground or low in shrubbery. The best time to look for young peepers is in the early morning hours and in the late afternoon, when they tend to feed. Even if your timing is right, it can be challenging to find one — a full grown peeper is only ¾” to 1 ¼” long, and recently metamorphosed individuals are not much longer than ¼”, about the size of your baby fingernail. You’ll know it’s young because of its diminutive size and its snub nose!
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Young Wood Frogs Getting Land Legs
Thank you all for your good wishes regarding my next book!
With the dry weather we’ve been having, there is reason to be concerned about vernal pool residents, especially those that need to undergo metamorphosis before the pools dry up. Granted, those amphibians such as Wood Frogs and Spotted Salamanders which transform into terrestrial creatures have evolved to have very quick life cycles, due to the temporary nature of their aquatic environment, but were they quick enough this year?
A very young Wood Frog crossed my path yesterday and answered that question for me. No bigger than a raisin, it had to have emerged from its aquatic home in the very recent past. When you think about the changes that have to occur between egg stage and adulthood (a total of two months, and it takes three of those eight weeks for Wood Frog eggs to hatch), it is mind-boggling. Gills disappear and lungs develop, tail is absorbed, legs develop, mouth widens, intestines adapt to a herbivore-to-carnivore switch in diet – all inside of five weeks.
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Young Green Frogs Absorbing Tails
Generally speaking, green frog tadpoles that hatch early in the season will transform into frogs by mid-to late summer. Tadpoles that hatch late are likely to overwinter in their ponds and metamorphose late the following spring or early in the summer. Thus, the Green Frogs you see now with both legs and a tail spent the winter as tadpoles and are maturing now.
A specific process called “apoptosis” occurs as the tail is absorbed by the frog. It involves programmed cell death, and occurs in various forms in multicellular organisms. Humans experience apoptosis throughout their lives. It is responsible for the separation of fingers and toes in a developing embryo, as the cells between the digits undergo apoptosis and it is responsible for the death of between 50 and billion cells each day in the average human adult. Once it has begun, apoptosis cannot stop, and thus is a highly regulated process.
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