Founding Frog-ers

Gray tree frog

This colorful and shimmery frog could compete with any fireworks. (Photo by Brian Gratwicke, Smithsonian Conservation Biology Institute)

Frogs found within the United States of America can be red, white, and sometimes, in rare cases, blue. As their names suggest, the California red-legged frog (Rana draytonii), Northern red-legged frog (Rana aurora) and the American white-lipped frog (Leptodactylus fragilis) embody America’s more patriotic colors. Blue frogs, however, are a rare oddity, with the color sometimes appearing in bullfrogs, green frogs and leopard frogs that are deficient in yellow skin pigments. In honor of the Fourth of July, we thought we’d take a closer look at frogs found in the States.

The United States is home to a diverse group of frog species. According to the IUCN Red List, there are 87 species of frogs living in the United States. Texas has the most with 45 species, while Alaska has only three. In general, there is more diversity in the South, with states such as Alabama, Florida, Georgia, Louisiana, Mississippi and North Carolina hosting more than 30 frog species, according to the Association of Zoos and Aquariums.

Though most American species of frogs live in freshwater environments, the Southern leopard frog (Lithobates sphenocephalus) can live in brackish or saltwater habitats. Frogs in the United States also make unique sounds. The barking tree frog (Hyla gratiosa) is named after its low-pitched calls that sound like a dog or a goose. The dusky gopher frog (Lithobates sevosus) is an endangered species with a call that AmphibiaWeb describes as a “deep snore” or “outbound motor.”

Because of the changes in seasons in many places, some frog species in the United States have incredible ways of surviving cold weather too. The wood frog (Lithobates sylvaticus) freezes in the winter, letting its breathing and heart stop. Then, during thawing season, it resumes life!

Sadly, 10 frog species found in the United States are endangered. These frogs depend on us to protect their habitats and reduce the threat of chytrid, a fatal amphibian disease. On this day of independence, we should think about the wildlife that continues to define our country in unique and diverse ways.

The list of IUCN-listed endangered, critically endangered and extinct (in the wild) frog species in the United States includes:

  1. Relict leopard frog (Lithobates onca)
  2. Dusky gopher frog (Lithobates sevosus)
  3. Ramsey canyon leopard frog (Lithobates subaquavocalis)
  4. Southern mountain yellow-legged frog (Rana muscosa)
  5. Sierra Nevada yellow-legged frog (Rana sierra)
  6. Wyoming toad (Anaxurus baxteri)
  7. Arroyo toad (Anaxyrus californicus)
  8. Yosemite toad (Anaxyrus canorus)
  9. Houston toad (Anaxyrus houstonensis)
  10. Armagosa toad (Anaxurus nelsoni)

Nadia Hlebowitsh, Smithsonian’s National Zoo

The frog who cried “duck!”

Wood frog (Lithobates sylvaticus)

Wood frog (Lithobates sylvaticus)

Cute Frog of the Week: January 31, 2011

Don’t get confused if you hear a quack and there isn’t a duck in sight. You might’ve just heard the call of the wood frog, whose duck-like quack can be heard coming from moist wooded areas and ponds throughout the Northern United States, Canada and Alaska. If you see a small brown frog with a dark eye mask in the woods, it is likely to be a wood frog. There are no other species with a similar appearance in North America. This cute masked creature measures from 1-2 ¾ inches long and its color varies with temperature and gender; female wood frogs are often larger and redder. Reproduction takes place in late winter/early spring at ponds where there may often still be a layer of ice—but don’t worry about these frogs freezing! Unlike most other frogs, wood frogs can tolerate the freezing of their blood and other tissues. These frogs can survive many freeze/thaw events during winter, allowing up to 65 percent of their total body water to freeze. Cool, eh?

Photo entered by wombatarama at

Every week the Panama Amphibian Rescue and Conservation Project posts a new photo of a cute frog from anywhere in the world with an interesting, fun and unique story to tell. Be sure to check back every Monday for the latest addition.

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Brrr…it’s cold outside! How do frogs and toads survive?

Wood frog (Lithobates sylvaticus)

Throughout the winter, wood frogs (tadpole shown here) stop breathing, their hearts stop beating, and ice crystals form within their hibernating bodies. (Photo by: Brian Gratwicke, Panama Amphibian Rescue and Conservation Project)

Last week, as I was taking in the beauty of the snow-covered New England landscape, I started thinking about amphibians. With more than a foot of fresh snow covering the ground, I began to wonder where all of the frogs and toads go in the winter. We received so much snow from this recent snowstorm that I had to shovel a small path so our Boston terrier could navigate the backyard. If he needed help getting through the snow, how was a small frog or toad going to navigate the cold, wintry earth?

Well, it turns out that frogs and toads, particularly in the Northeast and other colder climates, spend their winters quietly tucked away while they hibernate in the mud at the bottom of lakes, carefully concealed in logs and tucked under leaf litter. Some toads even bury themselves to hibernate. Others continue to swim all winter long. Green frog and bullfrog tadpoles hatch in the summer and then spend all winter living and swimming below the ice in the nearly freezing water.

But none of these species compare to the wood frog when it comes to cold weather adaptations. This hearty frog is one of the more cold-adapted species with a natural habitat range extending farther north than any other amphibian species. In fact, the wood frog is the only frog found north of the Arctic Circle. These frogs hibernate during the winter in terrestrial or forested wetlands in very shallow earth. What’s most amazing is that the wood frog is so adapted to cold temperatures that its tissue can actually freeze and thaw.

Throughout the winter, wood frogs stop breathing, their hearts stop beating, and ice crystals form within their hibernating bodies, according to the Minnesota Department of Natural Resources. A special antifreeze they produce keeps liquids from freezing inside their cells and killing them. When spring arrives and the temperature rises, the frogs “thaw” and they emerge from hibernation.

The strategic advantage to this adaptation for the wood frog is that they are the first frogs out in the early spring, while other frogs are still hibernating deeper below. They are the first ones heard singing (the noise sounds like a chorus of “quacks”) and they begin breeding once they emerge. By late April, thousands of tiny black wood frog tadpoles can be found in vernal pools. Tadpoles develop quickly in order to metamorphose to froglets before the vernal pool waters dry up by late summer.

So, the next time you see a snowy landscape, take a moment to think about frogs and toads and their amazing cold weather adaptations. It’s incredible to think that just beneath the smooth sheet of glistening ice covering a pond that small tadpoles could be swimming through the freezing waters, or that a small toad or frog could be snugly nestled within a hollowed log deep in a winter slumber.

– Brooke Wardrop, Zoo New England