Hyla regilla
Pacific tree frog

Hyla regilla are found in the Pacific Northwest region of North America. This range extends from California to British Columbia, and from the Pacific coast east to Montana and Nevada (Hill, 2000). They are found from sea level to about 11,600-ft (Wright, 1995).

They are a very adaptable species. Contrary to their title, they usually live on the ground. They are found near springs, ponds, streams, swamps, and other moist places. They will live in damp recesses among rocks and logs and in dense vegetation. (Wright, 1995)

Tadpoles are about 1 cm long when they hatch, and they are grayish green in color. As adults, Hyla regilla grows from 1-1 7/8 inches long (Wright, 1995). Females tend to be slightly larger than males. They have sticky, circular disks on the ends of their toes that are used for climbing. They have a light underside and there are dark spots on their back and legs. There are black stripes, which start at the shoulder and go through the eyes. There is also a Y-shaped mark on the top of their head, between the eyes. Coloration varies between individuals, and also within an individual, ranging from lime green to brown. An individual can change shades depending on moisture and temperature. This is different from some lizards that can change color to match their background. (Hill, 2000)

Hyla regilla are solitary animals, but they sometimes congregate in large colonies during the breeding season. They are nocturnal and are also very territorial. At night, males repeat their dual-toned mating call to ward off other males from their part of the pond. This croaking is a kreck-ek in rapid sequence. It is surprisingly loud for the size of the animal (Wright, 1995). Hyla regilla also have the unique ability to change color. While this helps in camouflaging from predators, they cannot change willingly to match its background. Instead the change has to do with temperature and moisture. Predators include herons, bullfrogs, raccoons, and mink (Hill, 2000).

As tadpoles, Hyla regilla feed on plant material. When they transform into adults, their feeding habits change from plants to insects (tiny gnats, flies, and mosquitoes) (Krahling, 2000). They capture prey by flicking out the tongue, sticking it to an insect, and then bringing it back to the mouth. The tongue is specialized for this because it is coated with a sticky secretion, is relatively long, and is very quick. This procedure is a response to movement, which they detect with sight, smell, and hearing. The problem with this mode of feeding is that they pick up dirt and other debris with the prey, which cannot be sorted out, because they swallow their prey whole. They don't chew or break down their food (Tyler, 1976).

They are important to scientists because they are considered an "indicator" species. Since they are so sensitive to environmental change and water quality, they give us clues to the cleanliness and health of the ecosystem. The sticky quality of their toes has also caught our interest. In Scotland, researchers are studying the adhesive features of the toes to come up with new technology in the tires of cars (Krahling, 2000). People also keep them as pets, but they are protected by law and require a permit to keep and transport them (Hill, 2000).

In the Pacific Northwest, Hyla regilla are the most abundant amphibian species. Amphibians as a whole are very sensitive to environmental changes. Their numbers are declining world wide mainly as a result of poor water quality, which scientists attribute to rising amounts of acid rain (Krahling, 2000).

These frogs were of cultural significance to Native Americans. It is the belief of native Americans that an individual tree frog co-exists for every person. As a result of this belief, they showed great respect towards these animals.