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)
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.
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)
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.
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 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).
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.
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.
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)
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!
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)
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.)
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.
Congratulations to Naturally Curious readers for their familiarity with Eastern Gray Treefrog (Hyla versicolor) toe pads! This is the easiest time of year to find these amphibians, mainly because of their habits. During the fall, winter and spring treefrogs are usually silent, unlike the summer, when males can be heard calling their melodic trill from bushes and trees near bodies of water after the evening air temperature rises above 59°F. Because they are nocturnal, well camouflaged, and hibernate in the winter, you don’t often come across one except for the warmer months when males are calling. The colors of an Eastern Gray Treefrog (brown, green and pearl-gray) vary with the colors of its background and environmental factors such as season and humidity, but shades of gray are most common. Their green color is more prominent during the breeding season and in young frogs.
When hunting insects, or when disturbed, treefrogs can leap great distances and, thanks to advanced toe pads, when they land they can cling to practically any surface, including vertical branches and leaves that are wet. A very low angle between the toe pads and substrate as well as mucous glands located in channels between the hexagonal pattern on a treefrog’s toe pads have inspired the design for treads on car tires.
You can listen to an Eastern Gray Treefrog’s call by going to http://langelliott.com/calls-of-frogs-and-toads-of-the-northeast/ (Sound recording © Lang Elliott – langelliott.com)
The loose banjo string call of the Green Frog is a familiar sound near wetlands this time of year. Males (to the right in photo, with bright yellow throat) have been busy serenading females (to the left in photo, with white throat), in an attempt to breed with one. Female Green Frogs select their mate, a choice which is based partially on the suitability of the male’s territory (underwater plants are a plus). After inspecting several males’ territories at night, the female chooses one and slowly approaches him, turning to face away from him as their bodies come in contact. External fertilization takes place as he clasps her while she lays her eggs (known as “amplexus”).
Unlike Wood Frog eggs that are laid in clumps, or Spring Peepers’ individually-laid eggs, Green Frog eggs are laid in a loose cluster that often floats on the water’s surface (see photo) or is draped on underwater plants. Each cluster usually consists of 1,000 to 5,000 eggs that hatch in three to five days. Females sometimes return to breed a second time with a different mate, in which case the second egg clutch is usually smaller, consisting of about 1,000 to 1,500 eggs.
The larval, or tadpole, stage of a Green Frog lasts from 3 to 22 months, which explains why you might have already seen large Green Frog tadpoles this summer.
(Outstanding theories were submitted on yesterday’s mystery. Be sure to read comments!)
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Inevitably, as newly-emerged drying dragonflies and damselflies hang over the surface of the water on emergent vegetation, breezes blow and some of them lose their grip, falling into the water below. At this stage, their bodies are soft and they are not capable of flight, which leaves them very vulnerable to aquatic predators such as Eastern Newts. While amphibian eggs, aquatic insects, crustaceans, worms and small molluscs make up most of their diet, Eastern Newts are quick to make a meal of most invertebrates that end up in the water.
Pickerel Frogs emerge early in the spring from their muddy, pond bottom hibernacula, and mate in April and May in the Northeast. As part of the mating ritual, males call to attract females, with the calls resonating inside their internal vocal sacs located between their tympanum (ear drum) and foreleg (unlike Spring Peepers and American Toads, whose vocal sacs are located directly under their mouths).
These low-pitched calls resemble short “snores.” Occasionally Pickerel Frogs call from under water, but even when they are above water, their calls do not carry very far, frequently making it difficult for human ears to hear them. Their call is similar to that of the Leopard Frog’s but lacks the short grunts of a full Leopard Frog call. You can compare these two calls (and several others) by going to http://langelliott.com/calls-of-frogs-and-toads-of-the-northeast/ (Sound recording © Lang Elliott – langelliott.com)