Thanks to Trech for suggesting this week’s topic, the red-eyed tree frog!

Further reading:

Tadpoles hatch in seconds to escape predator

The colorful red-eyed tree frog [photo by Geoff Gallice]:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

This week we’re going to have a short little episode about a little frog, suggested by Trech.

The frog in question is the red-eyed tree frog, which is native to Central America, including parts of Mexico, and northwestern South America. It lives in forests, always around water. You might be thinking, “of course, frogs live in water,” but remember that this is a tree frog. It lives in trees. But it still needs water for its babies, just not quite in the way most frogs do.

Before we learn about that, let’s learn about the frog itself. A big female can grow about 3 inches long, or 7.5 cm, while males are smaller. It’s a cute frog, of course, because frogs are always cute, but it’s also brightly colored. It’s bright green with red eyes, blue and yellow stripes on its sides, and orange feet.

Ordinarily, a frog with such bright colors would warn potential predators that it’s toxic, but the red-eyed tree frog isn’t toxic at all. Its bright colors have a different purpose. When it’s sitting on a leaf, the bright colors are hidden and only the frog’s smooth green back is showing, which makes it look like just another leaf. Only its eyes are bright, but it closes its eyes when it’s resting. But if a predator approaches, the frog opens its eyes suddenly and jumps up, revealing all those bright colors. The predator is startled, and maybe even hesitates because it thinks the frog might be toxic, and by the time the predator decides it should try eating the frog after all, the frog is long gone.

Oh, and if you’re wondering, the red-eyed tree frog can see through its eyelids. They’re actually not eyelids like we have, but a membrane that it can move over its eyes. The frog is nocturnal and eats insects like mosquitoes, crickets, and moths. It has a good sense of smell, which helps it find insects in the dark.

The tree frog also has suction cups on its toes that help it stay put on smooth leaves. During the day it sticks itself to the underside of a leaf to sleep where it’s more hidden. The female also lays her eggs on the underside of a leaf. This protects them from heavy rain, since the frogs breed during the rainy season, and it also helps hide them from predators. The female chooses a leaf that’s growing above water, and if the leaf isn’t very big she’ll lay eggs on both sides of it and fold the leaf to help hide all the eggs. The eggs stick to the leaf with a type of jelly that also helps keep them from drying out.

The eggs hatch in about a week, but they can hatch a few days early if a predator approaches. The embryonic tadpoles in their eggs can sense vibrations, and if a predator like a snake shakes the leaf as it approaches the eggs, the tadpoles can hatch within seconds. They drop straight down into the water below the leaf.

Hatching early when in danger is called phenotypic plasticity, and it’s really rare. It’s especially unusual because the embryonic tadpoles can actually tell the difference between a typical predator of frog eggs and vibrations caused by other animals or the wind. They can hatch so quickly because the stress reaction causes the pre-tadpoles to secrete an enzyme from their little noses, which weakens the egg wall and allows them to push and wiggle their way out.

Tadpoles stay in the water for several weeks, or sometimes several months depending on conditions, during which time they eat algae and other tiny food in the water. As they grow bigger, the tadpoles can eat bigger food, including other tadpoles. They switch to tiny insects after they metamorphose into froglets.

At some point during its development, a red-eyed tree frog needs to eat enough food containing carotenoids in order to develop properly, and in order to develop brightly colored skin as an adult. The red-eyed tree frog is a popular pet, but captive-bred frogs sometimes aren’t as brightly colored because they didn’t get enough of the right foods as young frogs.

During breeding season, a male will claim a small branch and jump and bounce around on it, both to call attention to himself and to shake other males off the branch. He also croaks loudly to attract a mate. This is what he sounds like:

[frog call]

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Thanks for listening!