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Roger Weller, geology instructor

Tree Frogs
by Amanda Anderson
Physical Geology
Spring 2007



Pacific Tree Frogs

            The start of the Pacific Tree Frog, also known as Hyla Ragilla, just like the rest of life, came from the first amphibians that made their way from the oceans to land. Because frog’s skin and tissue are soft and they live in cool, humid climates, it hard for a good fossil to be made of them. Although scientists are not sure which amphibian line frogs come from, they believe the frogs from today descend from the lobe-finned bony fish. These fish had lungs and limbs that let them crawl onto the land. The Pacific Tree Frog is a species from the Hylidae family which have fossil records dating about 50 million years ago in the Paleocene. The Hyla group is thought to originate in South America, about 65 million years ago in the Tertiary period. They then made their way up to Mexico and then to east coast of North America, mostly California, where they adapted to the environment and live today.


            The Pacific Tree Frogs look very different from other frogs we see today. These frogs are so small they are sometimes hard to find. The adults grow to become between three-fourths of an inch to two inches long with a wide body. The frogs can come in many different colors and they can change their skin tone fairly rapidly. Their color can be anywhere from tan, bronze, or gray to brown, or even bright green. Unlike most animals that change colors, the Pacific Tree Frog does not change its skin tone according to its background, but rather from the humidity in the air and the temperature and can take up to ten minutes to change its color completely, giving it camouflage protection. A distinct characteristic to the Pacific Tree Frog are two stripes starting at the nostrils going over each eye and fading as they lead back. There underside is light colored and can have dark spots on the belly, legs, and back. The female frogs are always larger then the males, while the males have dark throats; this is from the skin stretching while the males release their mating calls. The frogs have sticky pads on their feet to help them climb plants, trees, and even glass. They use these pads to climb plants and jump from leaf to leaf searching for insects they can feed on.

Pacific Tree Frog on a dime

The Pacific Tree Frogs mating techniques are unusual. The male frogs would find little shallow waters and then congregate there, using a certain type of croak that will lure the females. These croaks were so loud they could be heard anywhere from half a mile to a mile away on a quiet night. The females then come to the males where they would have to touch them to get their attention. Females then head towards the water while male follow. The males then grab the hind legs of the female, where they may wait for long periods of time; maybe even up to hours before the eggs begin to be laid, there can a numerous amount of eggs laid, anywhere from five to seventy eggs at a time. When the eggs are in the process of being laid, the males fertilize them externally. The frogs lay their eggs in the shallow ponds and attach them to materials they find in the water, such as twigs and moss, because other animals that are threats, such as bull frogs and snakes are usually do not come around these areas. The two frogs then leave the eggs, the female looking for areas with more moisture; the eggs have to for themselves.

Depending on the temperature it can take the eggs three to seven days to hatch into tadpoles. First eating the jelly eggs they just wiggled out of, the tadpoles then feed on anything that is floating around in the water surrounding them. The little tadpoles swim around aimlessly for about three months where they then transform into little frogs. If the water is warmer, it speeds up the tadpoles’ metabolism which in turn speeds up their maturing process.


















photo by Purnima Govindarajulu


The Pacific Tree Frogs mature fast and it is argued whether or not they become sexually mature within the next year or two years. The process then repeats itself with each new generation. 





                                                                                                                  copyright Paul Grace (