Speaking of Nature: Leap into summer with frog facts

  • Note the size of the tympanum (ear) on this female green frog. Also note the bright color of the skin, which lets you know this female is warm in the sunshine. For The Recorder/Bill Danielson

  • Look at the size of the tympanum (ear) compared to the eye and you can see that this is a male green frog. For The Recorder/Bill Danielson


For the Recorder
Monday, June 25, 2018

The first half of 2018 has been peculiar to say the least. I have no particular explanation for this, but there is definitely evidence to support this claim. My journals are thinner than they have been in past years and I’ve only taken about 30 percent of the photos that are normally “in the can” by the end of June. I feel like I’ve lost track of things, which is an odd feeling for someone who keeps such close track of things.

So, that symbolic moment when we officially moved from the spring so summer came as a bit of a shock. It just happened to be that the first day of summer was the last day of school, so there was a great deal of attention paid to the date on the calendar, but that didn’t alleviate the peculiar feeling that accompanied it. I sort of blinked, as if waking up from an unexpected nap, and looked out at a world that had moved along without me.

The first hint that something was amiss came on Father’s Day. I was sitting in the backyard of my parents’ house and enjoying the verdant surroundings that reminded me of a Thomas Cole painting, when I happened to notice a frog. It was floating next to the edge of a log that protruded at a gentle angle from the surface of one of the pools in their backyard stream system. I’ve seen frogs next to this log for years, but I realized on that particular day, that the frog was the first I’d seen all year. Peculiar.

The frog was a green frog (Rana clamitans) and it was clearly feeling chilly. I could tell this by observing the dark color of its skin, which is normally a brighter green. It turns out that green frogs can change the color of their skin from a bright, vibrant green to a darker brown that reminds me of an avocado. There can be a lot of color variation from one individual to the next, but at no point, however, is this species ever entirely green. The hindquarters always have dark markings on them.

The green frog is easy to identify because of a simple feature of the skin that is readily observable by anyone. Starting from the general area of the eye and extending along the back is a long, linear fold of skin. Again, this particular feature appears to be more pronounced in some individuals, but if you see it, then you know you are looking at a green frog.

Once you have determined the species you are looking at, you can even identify the sex of the particular individual you see by scrutinizing another physical characteristic that is easily observable by anyone. Specifically, you want to look at the frog’s ear. Also called a “tympanum,” the ear of a green frog lies behind the eye and varies in size according to the sex of the individual. Males have ears that are roughly twice the diameter of their eyes, whereas females have ears that are roughly the same diameter as their eyes.

Then, of course, you can distinguish a male frog from a female if you hear it singing. To my ear, the song of the green frog has always sounded like a banjo string being plucked with too much force. You can make an approximation of this sound by gulping air into your throat while you also use your muscle memory to try to say “Grrr.” As male green frogs sing, their entire body seems to get involved and the final note makes their bright yellow throats expand.

Males attract females with their singing and mating will ensue. Female green frogs lay masses of eggs that resemble large blobs of gelatin filled with little black spots. Such masses can contain hundreds of eggs and a single female can lay between 3,000 and 5,000 eggs in a breeding season. The masses are anchored to vegetation under the water and as soon as the eggs hatch, the surrounding water will be filled with little tadpoles.

Depending on the quality and latitude of the habitat, green frog tadpoles can develop into the frog phase in as short a time as three months, or as long as two years. Young frogs can be especially fun to look for in the later parts of the summer because of the funny noises they make. Just walk to the edge of a pond and listen, and you will probably hear the high-pitched notes of young frogs as they launch themselves into the air and dive underwater for safety.

Better yet, try to see these young frogs before they jump. It is much more difficult than it sounds. Frogs have outstanding eyesight and they are particularly good at picking up on objects in motion. The older frogs at my parents’ house have become somewhat docile simply because they have acclimated to the presence of people, but frogs out in a natural pond are generally difficult to approach. They are so good at blending in that I generally see them after they have leapt into the air, but a cool morning is always favorable because the cold-blooded frogs will be quite sluggish.

I hope your last week of June is a pleasant one. Perhaps, to celebrate the arrival of summer, you can head out for a day spent exploring the margins of a local pond. If you are able to find a frog, see if you can determine its sex and species. Remember to look for that lateral fold of skin on a green frog. If the frog you see is lacking this feature, then you’ve found something else. Next week, I’ll try to provide an answer to this mystery.

Bill Danielson has been a professional writer and nature photographer for 20 years. He has worked for the National Park Service, the U.S. Forest Service and Massachusetts State Parks, and currently teaches high school biology and physics. Visit www.speakingofnature.com for more information, or go to Speaking of Nature on Facebook.