Thu. Feb 29th, 2024
Wood Frog.

Today’s post comes from the Charleston Lake Discovery staff.

Frog lovers will not be disappointed with Charleston Lake Provincial Park. Larger frogs, such as bullfrogs, green frogs, and leopard frogs, are easily seen or heard in ponds, shorelines, wetlands, and grasslands.

But it’s a shame that another common park frog goes unnoticed and underappreciated.

It probably goes unnoticed due to its small size and the fact that breeding males only call for a short period in early spring. Their elusiveness is further intensified by the fact that they leave their breeding ponds immediately after the brief mating period and live most of their lives on the forest floor in relative silence. In fact, they are rarely found in water.

This modest, land-loving frog is appropriately called the Wood Frog and spends much of its time in the forest.

The toughest of frogs

The wood frog has a distinctive appearance, if you are lucky enough to see one, with brown or reddish-brown skin and a characteristic dark mask over the eyes. Adults measure between three and eight centimeters long.

wood frog.

They are very common in northeastern North America and range farther north than any North American frog. They can even be found beyond the Arctic Circle, quite surprising for a cold-blooded animal!

What it lacks in size and sound volume, it surely makes up for in tenacity and ingenuity. Few animals are able to perform the wood frog’s fabulous survival feats, such as resisting internal frostbite, hypothermia, and diabetes-like conditions, and then seemingly coming back to life.

We consider this amazing amphibian as an unsung hero and that is why we would like to show the wonders of this “wonder frog”.

without wasting time

Let’s start in early spring, when this frog is one of the first amphibians off the starting blocks.

After overwintering on land, hibernating under leaves on the forest floor, they immediately head to their preferred breeding ponds in the forest with the first warm (5°C) spring rains.

They may even begin breeding while there is still some snow on the ground and ice on the edges of their breeding ponds.

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To hear a wood frog’s call (which sounds a bit like a duck’s quack), you need to listen closely in late March or early April.

Wood frog in the grass.

Wood frogs are “explosive breeders” and compete in a reproductive race against time. They breed in temporary shallow ponds in the forest (free of predatory fish) that will dry out in the summer. Therefore, they need to breed early to allow their eggs and then tadpoles to develop before their pools dry out.

Therefore, the mating period is very short.

The annual meeting

These frogs migrate a lot, and the entire population of the area will travel at night, with most arriving on a particular night (although nearby pools may have slightly different hours).

It has been recorded that up to 4,000 people flock to a single pool in a three-hour period.

Once in the breeding ponds, many males begin singing (an energy-consuming activity in itself) and have wrestling matches between competitors, fighting for position to breed with females that enter the ponds. This is a remarkable feat considering that wood frogs have not eaten for about eight months and still do not feed until after the breeding period.

A single female can lay 500 to 3000+ eggs. Surprisingly, females have the uncanny ability to avoid laying their eggs in ponds that have fish (which could easily decimate the eggs and emerging tadpoles).

Adults only remain in the breeding ponds for a few days (usually no more than two weeks) before returning to the forest.

This may be the last time many of the adults will be in the water, as many will not survive to breed again next spring. They can travel between 400 and 800 m (some more than a kilometer!) from their breeding areas, a significant distance for an animal less than 10 cm long that moves by jumping.

In their race against time, frog eggs develop quickly, in as little as four days or as long as weeks (the warmer the temperature, the faster the development). The tadpoles grow rapidly and transform into young frogs within six to 15 weeks.

Outwitting the prey

Adults spend the rest of the spring and summer on the forest floor foraging for food while avoiding potential predators. They feed on a variety of invertebrates, including ground beetles, crickets, stink bugs, caterpillars, worms, snails, and spiders.

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A ribbon snake next to a wetland.A ribbon snake would happily eat a wood frog

Predators of adult wood frogs include larger frog species, snakes, herons, raccoons, skunks, and mink. When disturbed on land, they often make a few erratic jumps and then freeze, seemingly disappearing into the leaf litter and vegetation.

diabetic induced comas

In late fall, wood frogs exhibit perhaps their most notable survival strategy: they freeze for the winter!

For most animals, frostbite means certain death, but not for wood frogs.

Many insects develop cold-tolerant chemicals beforehand, while some plants “harden off” for the winter.

Surprisingly, Wood Frogs do not undergo any internal preparation.

Wood frog on leaves.

Rather, they wait for ice to form on their skin. But incredibly, about five minutes after their skin starts to freeze, the frogs react by producing huge amounts of glucose (a common sugar) in their blood and tissues. Glucose acts as a natural antifreeze, causing ice to form within the spaces between the frog’s cells, not inside the cells (which would be fatal). Up to 65% of the total water in a frog’s body can freeze!

Frogs will accumulate massive levels of blood glucose at a phenomenal rate, causing us humans to go into a coma. After freezing, wood frogs will have blood glucose levels about 45 times higher than the average person and, surprisingly, do not appear to suffer from diabetes or other ill effects.

Seasonal dormancy and resurrections

Wood frogs spend the winter on land, crouching on the forest floor with their heads down and limbs stuck to their sides, often simply under fallen leaves or logs, and then covered in snow.

They do not suffer hypothermia or frostbite.

While they hibernate, they will not breathe, their heart will not beat, they will not digest food or have brain cell activity. A human found in this condition would be declared clinically dead.

However, in the spring the wood frogs noticeably thaw and “come back to life.” They show normal body responses within 24 hours of thawing (in a laboratory), with full recovery within several days.

The wood frog is nothing short of a biological marvel.

They breed in early spring, when there may still be snow and ice, and fight against time to get their tadpoles to develop before their breeding ponds dry out.

wood frog.

In winter they can freeze (certain death for most animals) and then “come back to life” the following spring.

This wonderful frog challenges the limits of animal survival. Not bad for a simple little frog!