Benchmark of spring—the peepers are back!
By Shirley Murtha
For the past couple of weeks, we've been hearing that iconic audible performance that means spring has finally arrived: the mating call of the tiny amphibian known as the spring peeper, or Hyla crucifer. For such a small creature (an inch or just a bit over), the little frog has really got a set of pipes!
Actually, the "pipes" is a thin membranous vocal sac, an out-pocketing from the floor of the mouth. When the frog wants to call for a mate, it closes its mouth and nostrils and expels air from its lungs (i.e. exhales). The air travels through the larynx into the vocal sac, which then inflates. Muscle contraction keeps the air moving back and forth into and out of the sac, which vibrates and the sound is produced. Larger frogs have two sacs, one on each side and they swell rather than inflate. The larger and thicker the sac, the deeper the sound, hence the "knee-deep" of the bullfrog as compared to the high-pitched peep of the peepers.
The cute little peepers are around all year, but we hear them only during the early spring mating season. As with many cold-blooded creatures, nature has provided a method for surviving the freezing cold of winter. In the case of the peepers, a high concentration of glucose (blood sugar) acts like an anti-freeze, keeping internal organs safe, with metabolism slowed down to a minimum. The animals spend the winter motionless under leaf litter until the temperatures rebound, in late March or early April here in our neck of the woods.
Peepers are a type of tree frog, with suction cup type toe pads providing climbing ability, although they don't go much higher than shrub height here in the northeast. Their species name, "crucifer," refers to the darker brown cross on their back, which shows up nicely against their lighter tan color.
They can inhabit ponds, but are also quite happy starting off in the temporary vernal pools formed in the aftermath of melted snow and ice. Because of their small size, they can find adequate moisture in the damp undergrowth of the woodlands.