Frogs leap into spring

There is a change and a charge in the air. Birds that had come south are moving back to their breeding grounds. Tree leaf buds burst forth with a green that seems to be life itself. Wildflowers are blooming with riotous colors on the hillsides. The songs of spring fill the air. Bird communication changes from feeding chatter to long melodious mating verses. The noise of spring is almost deafening.

It seems as if all of nature has lost her mind and released the boundaries of convention, being as loud and brash as possible.

Leading this marvelous spring chaos are the frogs, silent and unseen through most of the summer and fall. After the first few rains the male frogs awaken and do their best to be heard and found by the females.

Foremost in this frog racket is the Pacific tree frog, Hyla or Pseudacris regilla. From January to May, depending on temperature and latitude, breeding commences with the mating calls of the males. Once puddles and pools form on the landscape, males congregate along the water's edges, staking out temporary territories.

In order to attract females, the males sound a two-toned mating call similar to "kreek-eeck." The chorus, a group of several males, is led by a chorus master who initializes the call. The chorus master, a dominant male, is then joined by subordinate males. This mating song is meant to attract a female into the male's territory so that breeding can begin. Often an intruding male will enter the space, and the mating call will change to a onetoned encounter call. Usually once the encounter call is heard the intruding male will retreat. Occasionally both males will sound the encounter call until one surrenders. Rarely, a physical scuffle will ensue until one frog leaves the space.

Let's get together

Once a female enters the male's territory she touches the male in order to make her presence known because he is so engrossed in his singing. As with most species, mate selection is not random. Either large males or those with larger external vocal pouches seem to be preferred, perhaps because a bigger male helps more with the extrusion of eggs from the female or because the songs of large males resonate more deeply.

As the male recognizes the female they journey to the water where fertilization can occur. In their watery boudoir, he climbs onto her back and clasps her under the forearms in a position known as amplexus. The frog is so driven by the need to mate that other species should beware. It is not uncommon for other frog species, salamanders, debris or even other males to be mounted by the male Pacific tree frog in his mating frenzy!

Once in amplexus the pair may stay in that position for several hours until the eggs are extruded from the female, in part by the pressure of the male. The female will lay between 500 and 1,250 eggs per year. As she lays the eggs the male releases sperm onto the eggs for fertilization.

Once the eggs are laid and fertilized, the male and female part ways and return to a life of foraging for food, leaving the eggs unguarded. Over the next few months you can check ponds and creeks for gelatinous masses about the size of a ping pong ball. These masses represent successful courtships which all began with a spring mating call. Each mass contains approximately 100 eggs which will become tadpoles in three to seven days.

Tadpole time

The egg mass sustains the tadpole for its first two days, but then the tadpole will turn toward decaying matter and live green plant materials for food.

Life is difficult as an egg or tadpole. It seems every creature under the sun appreciates the early amphibian as a food source. I have seen garter snakes and crows on the water's edge lapping up tadpoles by the dozen. In addition, other amphibians, small mammals, large insects and fish are all predators of tadpoles and frog eggs.

In approximately three months tadpoles morph into froglets. It has been found that Pacific tree frogs have acquired a unique trait that helps speed up the time of metamorphosis. In large congregations, tadpoles will situate their dark dorsal surfaces to face the sun. These dark surfaces act as solar panels to heat up the water surrounding them. The warming of water temperature causes an increase in metabolism and the speed of metamorphosis, therefore shortening the vulnerable tadpole stage.

There is much debate over the age at which the Pacific tree frog reaches sexual maturity. Some believe they are ready to breed in the first year while others contend it is not until their second year.

Regardless, the Pacific tree frog is prolific, making it Southern California's most heard and seen frog.

The males are obviously doing something right with their loud and uncontrolled spring melodies.

Meghan Walla-Murphy can be reached at the following e-mail: mwallamurphy@yahoo.com.