The recent rainy weather we experienced before the July 4th holiday brought a welcome break from hot summer weather. While the rain brings evening coolness, it also brings something else – amphibian mating calls. We've had a regular little froggy chorus going on in the side yard next to our porch the last few nights. One little character got so loud that it peaked my curiosity and I couldn't help myself – I just had to grab the flashlight and investigate further. He sounded pretty close, and I was determined to "find and identify".
All frogs are amphibians, a Greek word that means "double life". They start life hatching from water-logged eggs as tadpoles with fish-like bodies (including gills) and gradually develop limbs and lungs so they can eventually live on land. The tadpoles (larval stages) of frogs will vary in size and coloration, depending on the species. There may be slight differences in body morphology and mouthpart structure, but all frog tadpoles primarily feed on algae and small bits of plant material in the water. As they grow into the later stages, they will become more opportunistic in their feeding and may also eat small insects and animals. They feed almost constantly as their bodies morph into the adult frog form. As the lungs develop inside, the gills get smaller and the tadpole spends more time near the surface, taking in gulps of air with increasing frequency. Gradually it stops eating and the tail tissue is absorbed as food until it finally disappears. The strong hind legs are now being used for swimming, and the tadpole has been transformed so that it looks more like an adult frog.
How long does this process take?
That depends on the species and its respective lifestyle. There are 21 species of frogs and toads in Illinois that we know of. The largest Illinois species, the bullfrog, may take two years to turn from tadpole fresh out of the egg into a small frog. This species' larval stages inhabit permanent pools and usually take longer to metamorphose. They're not extremely active in the tadpole period and have secretive habits that don't readily expose them to predation. This tadpole typically reaches a larger size than those of other frog species that inhabit more ephemeral (short-lived) bodies of water, such as puddles and shallow pools. Frog species that utilize these areas are usually fast-growing, are quite active, eat voraciously, and have relatively short larval periods. Since they grow up so quickly, the new froglets are generally quite small and more vulnerable to predators. Because small ponds and pools can dry out fairly quickly, the whole process from tadpole to frog may take only a month or two. This is true in such species as wood frogs, tree frogs and spring peepers. They must mature and leave their watery home before it disappears for good. Predators of all kinds can be a problem for these small creatures as they leave the water and hop away to nearby forests and fields.
Why do frogs croak?
The vocalizations we hear on cool, rainy evenings are the mating calls of the male frogs as they arrive at their breeding spots. Each species has a distinctive croak, squeak, trill or "ha-rumph", but they all mean the same thing to the female – "pick me!". Most females do not vocalize, but in a few species the female does call in response to the male. (Both genders of many species will emit a loud distress call when caught by a predator, however.) The males of the same species will often croak alternately back and forth to each other in an effort to warn likely competitors to "keep away!". (This behavior has definitely been going on in our yard.)
How do frogs differ from toads?
Though similar in many ways, frogs and toads are really not difficult to tell apart. A frog's skin is moist and smooth, while a toad's skin is dry and rough or "warty". This enables a toad to live farther from the water than a frog. Frogs have large and powerful hind legs for jumping and swimming, while a toad's legs are shorter so it can only manage short hops. A toad generally has a fatter, chunkier appearance, while frogs are more elongate and stream-lined. A toad will squat down and stay motionless when it senses danger, while a frog uses its jumping ability to flee its predators. Frogs become prey to many other animal species, but toads excrete a moist material from their skin that irritates the eyes, mouths and nasal membranes of its predators, so they're usually left alone. The frog's moist skin requires that it remain in or near water, while toads are commonly found in areas that offer moist leaves or loose soil that they can burrow under to stay cool during hotter periods, so they don't need to live close to water to survive as adults.
The evening of our frog search found us waiting patiently for the next loud "trill", each one helping us to zero in on the little creature's hiding place. My assistant (my visiting college-aged, youngest daughter) and I worked as a team. I held the flashlight while she carefully waved aside plant leaves, and we both peered intently in the direction of the last froggy mating call. It took a while, but we eventually uncovered the little culprit. It remained motionless in the beam of my flashlight like the proverbial "deer in the headlights," clinging tightly to the cement of the little garden fountain it had chosen as its perch. She cupped her hands around it, and after several slippery drops to the grass, there was a lot of frantic alternate chasing and re-capturing. (The flashlight lady sure had her work cut out for her!). We finally managed to get it inside for further examination and identification. It turned out to be a little male gray treefrog (Hyla chrysoscelis-versicolor), and I think it must dwell in the hedge nearby. It was about the size of a half-dollar, and with those little toepads on its feet, I'm sure it has no problem climbing the woody branches to safety during the daylight hours. It was pretty cute.
We released the little treefrog back where we found him, hoping that his impromptu encounter with curious humans would not impair his ability to resume his place in the nightly frog chorus. I sure hope he finds his girl. I don't think he was too worse for the wear, though -- I've heard him trilling his little heart out every night since!