Last Thursday night it started to rain. The air became warm and humid and reminded me that we had not had a good rain in a very long time. The ground has been wet and muddy from snow melt, but it has been many months since a large, Gulf of Mexico air mass had eased its way across Western Pennsylvania. The rain continued into the early hours of Saturday morning and gave us a good couple of inches of water which we needed very badly. The rains also roused the spring peepers from the last of their hibernation hangover and stimulated them to start their nighttime choruses in the ponds and puddles all over western Pennsylvania. .
The spring peeper’s scientific name is Pseudoacris crucifer (which translates to “false locust” (for its insect-like call), and “cross” (for its distinctive X-shaped marking on its back). It is a small tree frog that lives around marshes, ponds, and temporary pools throughout the United States (except for the deep southeast). It is especially abundant here in the northeast. It has sticky foot pads that enable it to easily climb up the trees, shrubs, and tall grasses that surround its “home base” water source. It is from these perches that the male peepers sing out their distinctive, spring mating songs,
These mating choruses begin in early spring (around here usually in mid-March, but this year the first week of April) typically 15 minutes or so after sundown. The calls require a very large expenditure of energy by each individual which may explain why the males bunch together to form large, high volume ensembles (even though these groupings greatly intensify mating competition between individuals). Each frog is able maximally to make 90 calls per minute over a four hour chorus time. The mating/calling season only lasts for four to eight weeks. Male peepers begin to sing when they are three years old and the age, size, and overall health of the frog greatly affect the calling frequency. The temperature of the evening also affects calling patterns. On warmer evenings the frogs call much more frequently.
Females, attracted to the calling of the males, enter the calling area and select the individual with whom they want to mate. The male then clasps himself onto the female’s back and remains there as the female return to the water source to deposit her eggs. The attached male prevents other male from mating with the female and insures that all of the female’s eggs will be fertilized by his sperm. The female can lay between 800 and 1000 brown-colored eggs which may be deposited singly or in groups. Sometimes the eggs are set afloat in the pond water, sometime they are attached to submerged vegetation, or put into the mud, or into fluid filled tree hollows, or into many other types of available micro-pools.
The eggs take between six and twelve days to hatch. The larval frogs that emerge from the eggs (the “tadpoles”) are short with prominent dorsal fins. The tadpoles will remain in their aquatic form typically for ninety to one hundred days. This larval incubation can, however, be as short as forty-five to sixty days depending upon weather conditions, time of egg deposition, and conditions in the tadpole’s pool. Populations of peepers being reared in temporary pools may be undergoing selection for shorter and shorter larval incubation times. The devastating effect of the drying up of the pool is an unforgiving selection force. The tadpoles eat a wide variety of foods (including algae, dead vegetation, bacteria, fungi, zooplankton, flesh from animal carcasses, and even inorganic materials like sand). The tadpoles are in turn preyed upon by almost any organism that is larger than they are. Fish are especially significant tadpole predators in ponds, but predaceous beetles, salamanders, and water snakes also readily consume the tadpoles. Further, pesticides and other pollutants (including acid rain) are also significant agents of mortality in spring peeper tadpoles.
The metamorphosis of the tadpole into a frog begins with the appearance of hind limbs which is followed by the emergence of the forelimbs and the shrinkage of the tail. Jaws with teeth, eyelids, mucous glands in the skin, and finally the transformation of the light cartilaginous skeleton of the tadpole into the denser, bony skeleton of the frog complete the metamorphic transition into a tiny frog. The emergence of the frog onto land exposes it to even more predators and environmental dangers.
The frogs are readily eaten by snakes, turtles, birds, and mammals like chipmunks and muskrats. They are also frequently killed on roadways by passing cars and trucks. Peepers are also susceptible to many viral and bacterial illnesses, exhibit a wide range of benign and cancerous skin and mucous membrane tumors, and are beset by a wide range of endo- and ectoparasites (including tapeworms, flukes, nematodes, protests, and larvae of several dipteran species. Destruction of their aquatic habitats and even more subtle alterations of the forest cover around their wetland breeding sites can deleteriously affect the breeding potentials and survival of this small amphibian.
The spring peeper has been overwintering in an inactive, hibernative state under soil and leaf litter, in and under rotting logs, and even under rocks. They are frequently exposed to sub-freezing temperatures during their winter hibernation and are able to insure their survival in a frozen state by generating large quantities of glucose from their livers. This sugar (like we have seen in wood frogs and tree frogs) acts as a natural anti-freeze in their blood and other body fluids. Survival during these sub-freezing events is inversely related to the duration of the exposure (85% of the frogs survive after three days of freezing, about 50% survive after seven days of freezing, and 0% survive after twenty-eight days of freezing). While in hibernation, the peepers may also be preyed upon especially by small mammals active in the subnivian space beneath the snow cover. Shrews in particular readily consume the inactive, hibernating frogs. Long, cold winters, then, via extended lethal freezing and increased predation opportunities can have significant impacts on the population of this important sign of spring!
Fortunately, even after the long, cold winter we have all just endured, some of the peepers have survived. A chorus of peepers near campus has been heard singing at night, and several students have reported hearing other choruses near their homes. The chorus near our house in Armstrong County, though, has not yet begun to sing, although last night I did hear some tree frogs trilling. I hope that the winter has not been too hard on our local peepers!