Pacific Tree Frog
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[Photo] Pseudacris regilla - Pacific tree frog; Hyla is an old name. Source: USGS, http://www.werc.usgs.gov/fieldguide/hyre.htm Photo by Chris Brown

The Pacific Tree Frog is a very common species on the west coast of Northern California. They live everywhere from sea level up to over 11,000 ft. They are found in shades of greens or browns and even have been known to change between them. They live in many types of habitats and reproduce in aquatic settings.

Anatomy and morphology
The Pacific tree frog can reach up to about 5cm long from snout to urostyle. The males are often smaller than the females and have a dark patch of skin on their throat. This dark patch is the vocal sac which stretches out when a male is calling. These frogs can have highly variable color on their bodies. They can be any where from gray, brown, tan or bright green and can even change between them. They are usually a pale or white color on their bellies. They have many variations of markings on their back and sides that are usually dark and spotty. The one identifiable mark is a dark stripe that goes over the eye from the nose to the shoulder. Their skin is covered in small bumps. They have long legs compared to their bodies and they tend to be slender. Their toes are long and are only very slightly webbed. On the end of each toe, there is a round sticky pad that is used for climbing and sticking to surfaces.

Geographic distribution and habitat
Pacific tree frogs are most common on the pacific coast of California, Oregon and Washington, but they are found anywhere from Baja California all the way up to British Columbia. They are also found eastward to Montana and Nevada. They love water, but they can also be found upland from ponds, streams, lakes and some times even further away from water. Their habitat consists of a wide variety of climate and vegetation from sea level to high altitudes. The tree frog makes its home in riparian habitat as well as woodlands, grassland, chaparral, pasture land, and even urban areas including back yard ponds.

Reproduction, development and behavior
The Pacific Tree Frog begins mating in early winter to early spring. Since these frogs are so widespread geographically, it is thought that their breeding season is determined by local conditions. When it is time, the males migrate to the water. They all call at the same time very loudly. This lures the females to the water and they mate. The females lay their eggs in clumps of 10-90 and usually put them on and under vegetation and leaf litter in the pond. Females usually lay their eggs in shallow, calm water that has little action around it. If they are not eaten, embryos will hatch into tadpoles within one to three weeks. The tadpoles feed on periphyton, filamentous algae, diatoms and pollen in and on the surface of the water. They feed using a beak like structure that helps scrape vegetation off surfaces and suction. Metamorphosis follows about two to two and a half months later. Prior to transformation, they stop feeding for a short time while their mouth is transformed from herbivorous to carnivorous. Then the tiny baby frogs emerge from the pond measuring as little as one centimeter. They hunt using their sticky pads to climb on vegetation and other surfaces. They eat many types of arthopods. Much of their diet consists of spiders, beetles, flies, ants and other insects. They mature very quickly and are likely able to mate in the next season after metamorphosis. Predators include snakes, raccoons, herons, egrets, and other small mammals and reptiles. The tree frog is mostly nocturnal, but can be spotted during the day. It spends a lot of time hiding under rotten logs, rocks, long grasses and leaf litter.

Evolutionary History
The evolutionary history of these frogs is a very interesting one that has recently been changed to better suit tree frogs. Amphibians themselves are thought to have descended from the lobe-finned boney fishes. These fishes had an ossified skeleton and emerged from the water as they developed limb girdles and terrestrial characteristics such as lungs and a neck. It is hard to figure out an exact frog lineage because of the lack of fossil record. The habitat in which these animals lived was moist and decay was quick. This was not helpful in preserving biological clues. The family of Hylidae is some what recent appearing around 50 million years ago. The genus Hyla was close behind appearing just after the dinosaurs went extinct. This genus originated in South America and expanded to the north into Mexico and eventually into North America. There was then a rise in sea level and the connection between the northern and southern populations was gone. They have been separate ever since and have become genetically distinct from one another. For this reason, the genus Hyla has been split into three separate categories. Aris, Limnaoedus and Pseudacris. This is where the current confusion has taken place. Although the Pacific Tree Frog has carried the scientific name of Hyla regilla for many years, the most current consensus among scientists is that they should actually be Pseudacris regilla. This is still not agreed upon completely and in the future we will see what becomes of these names.

Green and brown color morphs?
One of the most interesting features of these frogs is their ability to change color from brown to green. Previously, it was thought that there where two different fixed colors that an adult tree frog could be. Now it has been found that some of them are actually able to change between the two. They can also change from lighter to darker. These color changing morphs are triggered not by color change in their environment, but a change in background brightness. This type of environmental change would be caused by seasonal fluctuation. A change in the dorsal coloration of a color morph takes anywhere from weeks to months to change, but has been shown to be a very useful cryptic survival feature for these frogs.

Conservation status
These frogs are the most common frogs on the west coast of North America. Although the Pacific Tree Frog remains abundant, there has been a large increase in amphibian declines. Most populations of tree frogs appear healthy, but there is some evidence of declines. The cause has not been fully understood, but pollution, the introduction of exotic species and habitat loss are very high on the list of factors. Some ways to stop amphibian declines are by respecting and protecting amphibian habitat as well as supporting laws and legislation that help to do this. Another important way is to help limit pollutants that will end up in amphibian habitat (usually from agriculture and urban run off) by boycotting companies who are heavy pesticide users and by not pouring chemicals or pollutants down storm drains or in amphibian habitat.

Regional Importance
In 2007, the pacific chorus "tree" frog was named the state frog of the State of Washington. The tree frog is also a very important in all of the regions where it is found because it is a keystone species. Many other species such as garter snakes depend upon its abundance as a prey item for their survival.

http://en.wikipedia.org/wiki/Pacific_Tree_Frog

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