Pacific Tree Frog

Hyla regilla

synonym: Pseudacris regilla

Colleen Dzwonek

DESCRIPTION

Coloration

Hyla regilla have so many different color variations that they are sometimes mistaken for separate species. H.regilla are generally "ground color," shades of brown or green. H.regilla also exhibit red, gray and almost black varieties. A H.regilla can be a single color or a mixture of them, green and brown together are a common color pair, but any mix of color is possible as well as color hue variance. H.regilla are generally categorized by their predominant color. For instance, a primarily green frog, with brown side splotches, would be considered green.
: Despite the huge color variation among frogs, H.regilla are easily distinguished from other species of frogs by their "eye stripes." This stripe is a black or dark brown band of color. The stripe extends backward, one from either nostril, to the eyes and continues back through the ear ending at the shoulder. This dark "eye stripe" is often bordered below by a band of light color. The back, or dorsal side of H.regilla are often spotted or blotched lengthwise with darker patches of color usually brown or black. H.regilla sometimes also displays a dark brown or black V or Y shaped pattern on the top of its head between the eyes.
: The underside, or ventral side, of H.regilla is generally lighter than the frog's back a yellow or white color. In males the throat is darker, gray or black in color, indicating the vocal sac (Nussbaum et al. 1983).; Physical Features; H.regilla averages in size between 1 1/4 inches and 1 3/4 inches, but can be as large as 2 inches or around 50 mm. Like most tree frogs, H.regilla, has an extra cartilaginous element called a "intercalary cartilage" between the final and second to last bones on their "toes" and "fingers." This adaptation gives the "fingers" and "toes" more maneuverability, an aid to climbing.
: This adaptation allows the tips of "toes" and "fingers" to rotate so that the sticky toes pads can lie flush against irregular surfaces, creating a stable foot hold.
: H.regilla has slender limbs in proportion to its body. It also has limited webbing on hind feet and none on fore feet. Males are smaller than females.; Tadpoles; The upper body and tail are a shade of brown. Many have black splotches on their backs. Their undersides are whitish with a metallic iridescence. When viewed from above tadpole eyes are located at the outer margins of the head. All other tadpoles in Oregon have eyes that are set in from the margin, closer to the center of the head.

DISTRIBUTION

H. regilla is found in Washington, Oregon, California, Nevada and the Santa Cruz and Cerros islands. H.regilla's range in Oregon covers nearly the entire state. They range from the coast to the eastern base of the Cascades and down into the desert region of the Great Basin. H.regilla can be found at elevations ranging from sea level to 7,370 feet(2247m) on Steens Mountain.

HABITS AND HABITATS

Few North American anurans exploit such a variety of habitats as does H.regilla. Because of their wide range, they inhabit deserts, grasslands, mountains, and rain forests. H.regilla are primarily ground dwellers who, can be found among low plant growth, usually near water. Within their rages they can also be found in downed logs, under rocks, and even under houses, anywhere where adequate cover and moisture are provided.
: H.regilla feeds primarily on insects and spiders. The tadpoles feed on algae.

BREEDING AND REPRODUCTION

Season

Because of H.regilla's wide spread dispersal throughout a variety of habitats, their emergence form hibernation and migration to the breeding ponds is a function of temperature and thus varies with elevation. At low elevations, H.regilla breeding choruses can begin to congregate as early as January in tidal ponds at the coast (Jameson 1956). At higher elevations, 4000 to 6000 feet, choruses have begun as early as April and June respectively and lasted until August. In general, for low elevations the breeding season lasts from February until June. For higher elevations the breeding season lasts from June until July.

The Cycle

It is commonly thought that H.regilla (Jameson 1957) emerge from hibernation and begin moving to the breeding ponds in response to environmental changes, such as warm spring rains, and a response to accumulation of reproductive hormonal production. Most H.regilla will return to the same breeding pond year after year, some even traveling distances of up to one mile. Although most H.regilla have small home ranges, usually under 200m from the breeding pond. Males emerge from hibernation and move to the ponds first, with the females following a few weeks later.

Because H.regilla is able to utilize ephemeral ponds for breeding grounds, they can establish breeding sites in a number of locations: shallow vegetated wetland, wet meadows, forested swamps and even road side drainage ditches, anywhere with standing water for several months. This is useful in avoiding predation by a variety of animals common to year-round ponds such as fish and bull frogs. The preferred pond, however, is one that is warmer and more open, with surrounding vegetation for cover. This is because warmer water promotes earlier metamorphosis and provides a longer post transformation growth period before hibernation, larger individuals are less susceptible to starvation and desiccation in the winter months (Schaub and Brodie 1983).

Once the males have arrived at their breeding pond they begin a chorus. Congregations of chorusing H.regilla have been found to contain as many as 500 individuals, but usually less than 200 individuals around a single pond (Jameson 1957). Choruses may call for 24 hours during the peak of the breeding season. But as the season progresses, the chorusing is restricted to the hours of darkness (Schaub and Larson 1978).

H.regilla have been found to have three distinct calls (Snyder and Jameson 1965). The first is a diphastic call, used primarily for location identification, territory marking and attraction of the female. It has been described as a rib-it, kreck-ek, and wreck it in rapid succession. The second call is monophastic and used in response to movement by other frogs in the vicinity. The third call is primarily a challenge to other males. It consists of quick staccato notes. If an already chorusing frog is confronted by a new comer, both will sound the staccato call until either the invading male has retreated or the resident male accommodates the invader presence (Whitney and Krebs 1975).

Males, while chorusing, will remain mostly sedentary, but do defend a territory around themselves of approximately 50 cm. This is thought to be done to avoid interference by other males and allow the approaching females to reach the desired male. Females choose a mate in response to their calls. It has been shown that the female H.regilla are able to differentiate their own species mating call among all other calls (Whitney 1980).

Once the male has grasped the female aplexus can last for several hours before egg laying begins. Females lay between 400 and 750 eggs. The eggs are deposited in small clusters averaging 25 eggs a packet (9 to 90). The eggs are in irregular clusters attached to grasses, stems or sticks in quiet shallow water. Females do not lay their eggs in the territory defended by their mate (Whitney and Krebs 1975).

Females will almost immediately leave the pond after breeding, but males will remain for most of the season, and continue to chorus and try to attract new mates, often for several months. Males do eventually leave the pond and the early arrivals are replaced by late coming males.

DEVELOPMENT

Especially in warmer water the embryos develop rapidly and hatches in two to three weeks. The tadpoles metamorphose in June in lower elevation and late August in higher elevations. Once they have metamorphosed, the juveniles disperse out into the vegetation. They usually travel no more than 200 m, but longer distances are known to have been traveled by juveniles. The young frogs average one half inch and will reach sexual maturity in eight months and participate in the following years breeding chorus (Leonard et. al. 1993) .

After transformation the juvenile frogs will grow rapidly during the first summer, generally doubling in length in the first two months. H.regilla continues to grow through out their life cycle, but at a much less rapid rate. The average life span in the wild is three years.

PREDATION

Common Predators

Thamnophis sirtalis -common garter snake

Thamnophis elegans- western common garter snake

Rana Catesbeiana- bull frog

Raccoons

Owls

References

Jameson, D.L. 1956. Growth Dispersal and Survival of the Pacific Tree Frog. Copeia 1956 (1):25-29.

Jameson, D.L. 1957. Population Structure and Homing Responses in the Pacific Tree Frog. Copeia 1957(3):221-228.

Leonard, W.P., H.A. Brown, L.L.C. Jones, K.R. McAllister, and R.M.Storm. 1993. Amphibians of Washington and Oregon. Seattle Audubon Society.

Nussbaum, R.A., E.D. Brodie, Jr., and R.M.Storm. 1983. Amphibians and Reptiles of the Pacific Northwest. University Press of Idaho.

Schaub, D.L and J.H. Larsen Jr. 1978. The Reproductive Ecology of The Pacific Tree Frog (Hyla regilla). Heptologica 34(4):409-416.

Snyder, W.F., and D.L. Jameson. 1965. Multivariate Geographic Variation of Mating Call in Populations of the Pacific Tree Frog (Hyla regilla). Copeia 1959(2):130-142.

Whitney, C.L. 1980. The Role of the "Encounter" Call in Spacing of Pacific Tree Frogs, Hyla regilla. Canadian Journal of Zoology 58:75-78.

Whitney C.L., and J.R. Krebs. 1975. Spacing and Calling in Pacific Tree Frogs, Hyla regilla. Canadian Journal of Zoology 53:1519-1527.