05/1/14

Learning How Frogs See and Hear

Guest post by Wes Deyton

How Frogs See

Frogs, due to the positioning and design of their eyes have nearly a 360 degree view. This makes up for the fact that they are not able to turn their head and look behind them like other animals can. Frogs, with their nearly 360 degree of field of view, make it difficult for predators to sneak up on them. Frogs also are unable to move their eyes within their eye sockets like humans and other animals can. This causes a Frog to have to turn his head to line up with it’s prey.

American-Bullfrog-by-Wes-Deyton

Frogs cannot see while they are attacking prey, so they must have their prey lined up when they go in for the strike. They are unable see their prey while they are making a strike, because when their sticky tongue comes out to snatch up an insect, their eyes retract into the top of their head.

Frogs are near-sighted and they do not see very well at a distance. Their eyes are extremely sensitive to movement, so if a frog’s prey does not move, they will not detect it. They also have excellent night vision, due to a mirror like layer in the back of their eye called a Tapetum. The Tapetum helps frogs reflect and collect ambient light between the back of the eye and the frog’s cornea. Frogs also use their eyes in a rather interesting way. They are unable to swallow like humans and other animals, so they actually push their eyes down into their head to push their food into their stomach.

Frogs eyes come in all different colors, from copper to bronze, gold to silver, and orange to red, like the Red-Eyed Tree Frog. They have three different eye lids. The third eye lid is the most interesting which is a clear membrane, and is called a Nictitating membrane, and this eye lid helps the frog to see underwater as well as to hide from predators.

How Frogs Hear

If you have ever been outside on a warm night you know just how loud Frogs and Toads can be. Male Frogs and Toads call to attract females. Below is a video of an American Toad calling to attract a mate.


 
You can see in the video, a Toad’s eardrum is the circular indention behind their eyes. You can also tell from the video, this toad calls quite loudly. Frogs and Toads are able to call at upwards of 90 decibels. They have quite sensitive hearing, so the question is, how do they not damage their eardrums or deafen themselves with their loud calls?

Scientists have discovered that Frogs hear with both their ear drums and their lungs and a pressure system builds inside the Frog that minimizes vibrations from internal noises made by the frog.

To further elaborate on this, I need to talk about how a frogs ear drum works. A frog’s ear drum is called a Tympanum and works in very much the same way that our human ear drums work. A frog’s ear drum, just like a humans ear drum, is a membrane that is stretched across a ring of cartilage like a snare drum that vibrates. There is rod that is connected to the ear drum, which vibrates by sounds that come at the frog. That sound is just pressure waves. The rod sloshes around in the inner ear fluid, which causes microscopic hairs to move, which send signals to the frog’s brain for interception. A frog’s ear lungs also vibrate when sound waves come toward it, although they are less sensitive than the frogs ear drum.

Earth Day poster with frog photographer, Wes Deyton and designed by Susan Newman

Some frogs, like the Spring Peeper, pictured, have a call that is so loud, they can be heard up to one mile away. These creatures are so noisy, it is a wonder that they do not hurt their ears and deafen themselves with their own calls. Frogs have a very clever method of making sure that their own loud calls do not hurt their own hearing.

In 1988, Scientist Peter Narins, who is a professor at UCLA of Physiological Science, found that frogs have an internal pressure system, a closed air loop, that keeps the frog’s own ear drum from vibrating excessively from its own call. Scientists have found that pressure builds between their lungs and ear drum, which then equalizes the pressure between the inner and outer surfaces of the frogs ear drum, which greatly cuts down on the vibrations that a frog experiences, from their internal calls. It is also believed that another purpose of the closed loop pressure system, is so Frogs can detect the direction a sound is coming from with its lungs, that way they can escape danger while calling. Being in the vicinity of a frogs calling can subject a human to sounds so loud, that are upwards of 90 dB, which can cause discomfort and hearing loss for humans.

Sources: April Holladay: Frogs Can Hear Without Ears. 4/26/2001. Wes Deyton’s blog at Last Mile Photography

02/17/12

Listening to Frog Songs to Understand Climate Change

At Frogs Are Green, we’ve always been interested in the interconnections between frogs and the Earth. How is climate change affecting amphibian populations? Are we listening to what frogs are telling us about the health of our planet?

Recently, we read an intriguing article in the Deccan Herald (India), about how a team of scientists in India are literally listening to frogs to understand the effect of climate change on amphibian populations.

Three scientists, K.S. Seshadri with T. Ganesh, and S. Devy, were doing research 100 feet above the ground in the canopy of the evergreen forest in the Kalakad Mundanthurai Tiger Reserve. While getting drenched with rain, they heard a cacophony of frog songs. Intrigued by the songs that the rains triggered, they initiated a program to study frog calls to both monitor populations and to study the affect of climate change on frogs.

Volunteer examines the monkey-proof enclosure for equipment to record frog calls. Photo credit: K. S. Seshadri

Amphibian Meterologists

Frogs can tell us a lot about the weather. Their skin is extremely thin and sensitive; they respond to even small changes in atmospheric moisture and temperature. The scientists reasoned that an analysis of sound recordings, combined with readings from climate data loggers, could help improve our understanding of the impact of climate change.

Climate change seems to underlie many of the threats facing frogs worldwide. By monitoring the frog calls, an activity calendar for each of the indicator species can be made. This long-term monitoring will be invaluable in understanding the greater impact of climate change and also might help to save frog species.

Work station studying frog calls, high up in the forest canopy. Photo credit K. S. Seshadri

As the Deccan Herald put it: “Will the croak alarm finally wake us from our ignorant slumber? The answer lies in the future.”

For more information:

“What Frogs Tell Us About the Planet,” Decclan Herald, India

“Frog song and climate science,” Ashoka Trust for Research in Ecology and the Environment

04/22/11

Earth Day 2011 – The Earth is Calling

April 22, 2011 marks the 41st celebration of Earth Day!

© Frogs Are Green | Photograph by Richard D. Bartlett

We’d also like to point you toward our contest page. We just started receiving entries for our 2011 Kids’ art contest and the 2011 photo contest. So check out the rules and be sure to enter as many times as you’d like throughout the Summer.

Happy Earth Day everyone!

Susan and Mary Jo

02/22/10

Wood Frogs Are (Almost) Celebrating Spring

In October, when we wrote our post Winter Turns Frogs into Frogsicles, the wood frogs and spring peepers had settled down for their long (frozen) winter nap. This blog post from The National Parks Traveler, Frogs are a Sure Sign of Spring, But that Doesn’t Mean You Won’t Hear Them Now, reminds us that even though it’s still winter (at least in the Northeast), it’s almost spring for the wood frogs. As the snow melts and the frogs unfreeze in late winter/early spring,  the young frogs have one thing on their minds: the males start calling immediately to potential mates.

I found this lovely video on YouTube by someone called Mysterious Susan (not our Susan though). It does have a mysterious quality as a reminder of the cycle of life.

Also, check out this blog post, “As Winter Wanes,”  in the East Hampton (Long Island, New York) Star about what songbirds, salamanders, and other animals are up to as we approach spring and the daylight hours get longer every day.

11/4/09

Frog Call of the Week: Spring Peepers

Can you tell the difference between crickets and spring peepers? I used to get confused sometimes between the sound of crickets chirping and frogs calling. Some frogs have bird-like calls. In anticipation of next spring, and in hopes of becoming better Frog Watchers, we are highlighting one frog call per week. We’ll start with familiar frogs in North America, but will also feature frogs from around the world. Below you’ll hear spring peepers and crickets so you can learn to tell the difference. Actually, it’s kind of fun to play the videos at the same time, too!

Spring peeper calling:

Crickets chirping:

If you would like us to highlight a particular frog call, please let us know!

06/21/09

The Coqui, Pride of Puerto Rico

June is traditionally the month of the Puerto Rican Day parade in New York City, and in other cities around the country, so it’s a good time to celebrate the unofficial symbol of Puerto Rico—the common coqui, a frog species endemic to Puerto Rico. If you click on the video below, you will hear the sound of this frog that makes a ko-kee noise. Imagine a chorus of these frogs.

A friend from Puerto Rico says he remembers being lulled to sleep by the calls of the coqui. After the birds quiet at dusk, the frogs start their night music and sing all night long. A recent exhibit at the Bronx Zoo about the coqui brought a record number of visitors, who no doubt also had memories of being serenaded to sleep by this tiny (one-inch long) tree frog. Only male coquis sing—both to fend off other males and establish their territory and to find a mate. Here’s more info about this beloved island amphibian, whose numbers are declining due to deforestation, among other reasons.