Critter Corner No. 14

I unabashedly love the spring season here in Indiana. The steady progression of natural events – from the first leaf buds and flowers to the onset of morels and the return of Neotropical migrants – leaves me fascinated, entertained, and in awe of Nature’s annual power of rejuvenation. But, if I had to pick one occurrence that really signifies the onset of this favored season, it would be the re-emergence of two of our smallest Indiana vertebrates.

 According to my field notes the first, hesitant intonations of the Chorus Frog typically begin during the last week of February. Of course this is highly temperature dependent. With a warm spring, their calls may begin a week or two earlier. The Spring Peeper stays abed a bit longer than the Chorus Frog. The high-pitched whistles of this little anuran are added to the choral group a week or so later. Even then, I am often amazed at how these miniscule frogs manage to emit even their most plaintive calls when both he water and the early spring nights are so cold.

Most often these diminutive frogs choose shallow, ephemeral pools in which to do their chorusing. These pools may occur in flooded fields, roadside ditches, wooded hollows, and other low lying spots. Although such water is at risk of impermanence, temporary pools are unlikely to contain fish or turtles. Thus this choice of breeding habitat reduces the risk of predation upon eggs and larvae. Outside the breeding season both species are seldom seen. They move away from their breeding pools and spend much of their time hidden under leaf litter, tree bark, or other ground litter.

Of course reproduction is what all of their vocalization is about. Calling males of both species use their distinctive tones to establish a small breeding territory. Their calls are also meant to entice females to them. The call of the Chorus Frog (top photo) is most often likened to the sound produced by rubbing one’s finger across the teeth of a fine-toothed comb. The resultant “creeeeee-ick” rises in speed and pitch toward the end Although both frog species are often lumped as “peepers” by laymen, the call of the Spring Peeper more closely fits that description. Their call reminds me of a very high-pitched whistle repeated at intervals of 2-3 seconds. Sometimes a breeding pool of these frogs can produce a sound which, at close range, is almost deafening. Standing in the midst of such an aggregation, and trying to locate a single individual, is virtually impossible. Like trying to locate a chirping cricket, the cryptic nature of the sound makes for a difficult task.

The Chorus Frog (the Western subspecies at GPFWA) and the Spring Peeper are, as noted, quite small. Both have an adult body length of less than an inch. As a result, many people imagine that these are “baby” frogs of some sort. Of course, baby frogs are tadpoles and the young of these two species are no different. Like most other amphibians, these frogs practice external fertilization of their eggs. Anuran external fertilization is a bit more efficient than that of most fishes in that the former practice direct external fertilization. Among the fishes sperm is deposited into the water near the eggs or into the water over an egg-containing nest. With frogs (and toads), there is direct contact between males and females. The male grasps the female in an embrace know as amplexus. This brings their cloacal openings into close approximation. Thus, as the female lays her eggs, the male’s sperm can be more closely directed onto them. Both species under discussion here can produce hundreds of eggs. These are often affixed to pieces of vegetation in the water and appear as large globules of gelatinous material with the dark, oval eggs embedded within. The length of time necessary for the eggs to develop into tadpoles, and for the tadpoles to become froglets, varies with water temperature. The higher the temperature, the more rapidly the eggs and larvae develop. As a general rule, development takes a month or two.

The Chorus Frogs (Pseudacris triseriata) in our area are usually brownish in color dorsally with three dark stripes extending from the base of the head to the end of the body. The belly is lighter in color, trending more toward cream or whitish. The Spring Peeper (P. crucifer) has a dorsum which is a lighter in color than P. triseriata and is a more fawn or yellowish-brown hue. The back is marked by a dark “X” which gives the species its specific name. The thighs are usually marked by dark bars which abut the X-mark when the legs are folded at rest.

Like other anurans (frogs and toads), these two species are carnivorous. Being so small predicates small prey and so the Chorus Frog and Spring Peeper feed heavily on animals such as ants, flies, spiders, beetles, and lepidopteran (butterfly/moth0 larvae. Froglets utilize even tinier prey such as springtails and mites. Tadpoles of both species are primarily algae eaters. Both frogs are, in turn, preyed upon by a variety of other animals. These include birds such as herons and shrikes, snakes, mink, raccoons, and other larger frog species. Mortality is high among eggs and tadpoles but, once they gain adulthood, Pseudacris sp. may live two or three years in the wild.

Although diminutive, the Chorus Frog and Spring Peeper play important roles within their ecosystems. Both act as agents of insect control, including mosquitoes, and as noted provide food for a variety of other animals. Like other anurans, their disappearance from an area may be the “canary in the coal mine’ harbinger of habitat damage due to factors such as environmental pollutants. Thus these tiny denizens of the wetlands bear import for us humans as well.

So, lend an ear as you traverse the roads and levees of Goose Pond FWA and your surrounding environs. At this time of year, it will be practically impossible for you to miss one of Mother Nature’s most pleasing wakeup calls. Spring is here say the Chorus Frogs. Warm nights and fair days lie ahead chant the Spring Peepers. Listen, look, and celebrate the renewal of our natural world they sing.

Interested in frogs and toads? Here are some useful references.

The Spring Peeper

http://www.biokids.umich.edu/critters/Pseudacris_crucifer/

The Western Chorus Frog

www.biokids.umich.edu/critters/Pseudacris_triseriata/

Conant, Roger and Joseph T. Collins. 1998. Reptiles and Amphibians: Easter/Central North America. Houghton Mifflin Co.. New York.

Minton, Sherman A. 2001. Amphibians & Reptiles of Indiana. Indiana Academy of Science. Indianapolis.