Hyla regilla is a small frog, about 3/4 to 2 inches, that has expanded toe disks and a black eye-stripe (Stebbins 1985).
The stripe runs from the tip of the snout posteriorly through the eye to the forelimb insertion (Grismer 2002).
The stripe is hard to see in dark frogs, but it is always present. The dorsal coloration is highly variable, and could be gray, tan, green, brown, or black, and it may change color from dark to light within a few minutes. It often has a triangular dark spot on the head and dark spots on the back and legs, and the clarity of these spots changes as the frog changes its color phase. Its limbs are crossbanded or blotched with dark color, and the posterior has a yellow or orange color, especially on the under surfaces of the limbs, the rear of the femur, and in the groin. Males have a wrinkled and dusky throat. When the male’s vocal sac is deflated, often 8 to 12 longitudinal folds are present (Stebbins 1985).
It has webbed hind toes with a margin of the web between successive toes. Skin is usually smooth with a few tubercles but occasionally quite rough. It has a round tympanum, that is anywhere from 1/4 to slightly over 1/2 the size of the eye opening, located in the eye stripe. The thenar tubercle is elongated and ovoid, while the palmar tubercle is made of 3 small, closely associated tubercles totaling the size of the thenar tubercle (Stebbins 1951).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Canada, Mexico, United States
U.S. state distribution from AmphibiaWeb's database: Alaska, Arizona, California, Idaho, Montana, Nevada, Oregon, Utah, Washington
Canadian province distribution from AmphibiaWeb's database: British Columbia
Distributed from mainland British Columbia and Vancouver Island through Washington, Oregon, California, and the tip of Baja California. H. regilla can be found on Catalina, Santa Rosa, and Santa Cruz, islands off the coast of southern California, and on Isla Cedros, an island off the west coast of central Baja California. Distribution also goes east to eastern Nevada and western Montana. It lives in habitats from sea level to 11,000 feet in the Sierra Nevada (Grisner 2002).
It seeks cover in many places, including rock fissures, under bark, in vegetation along streams, in rodent and other burrows, in nooks and crannies in buildings, and in culverts. It can be found in springs, ponds, irrigation canals, streams, and other bodies of water, but it has also been found as far as ½ mile from water (Stebbins 1951).
Out of the water, it frequents habitats like grassland, chaparral, woodland, desert oases, forest, and farmland (Stebbins 1985).
Life History, Abundance, Activity, and Special Behaviors
Breeding: H. regilla breeds over a long period of time, from January to the middle of May, in marshes, ponds, lakes, reservoirs, roadside ditches, and slow streams (Stebbins 1985).
In interior British Colombia, it may breed in June and July also. Later breeding occurs in higher altitudes. Around January, at the beginning of the breeding season, large numbers of vociferous males congregate at transient rain pools and more permanent bodies of water. The females do not enter the water until later, when they are ready to lay. Usually, females enter in the late afternoon or early evening, and mating and egg laying usually occurs by the following morning. Females enter either by themselves or in small groups, so there are many more males than females, making immediate mating probable. Usually, there is a preliminary period of clasping that lasts anywhere from 4 to 24 hours in a laboratory, and probably about 4 to 10 hours in nature. The male tightly grips the female with is forelimbs, but does not contact her with his body behind his pectoral region except when inseminating eggs. The male’s legs are flexed in a sitting pose, and insemination occurs at the moment of the extrusion of the eggs. The male discharges a quantity of transparent semen by bringing his cloacal aperture close to that of the female. With a quick, firm extension, the male slides his feet posteriorly over the sides and hips of the female, then retracts to his previous position. Simultaneously, the female extrudes a clutch of eggs into the cloud of sperm. The female sometimes scratches the substratum on which the eggs are going to be deposited before releasing the eggs. As the female extrudes the eggs, her cloaca is brought close to this surface and their attachment is effected. The eggs may be removed from her cloaca by her tarsi through flexor-extensor reflexes. The interval between layings is usually 2 to 10 minutes, but could be longer. After oviposition, the frogs separate. Amplexus is pectoral, and may last from 8 to 40 hours or longer (Smith 1940).
Eggs: Clusters of eggs are deposited in a pond’s shallow water, usually at depths above 4 inches. The clusters can be attached to sticks, leaves, vegetation, or other objects, and they can also be found floating on the surface, usually attached to objects. Eggs are usually laid in loose clusters of irregular shape, and the cluster has 2 gelatinous envelopes. The outer envelope is 4.78 to 6.7 mm and is sticky, and the inner envelope is 1.88 to 2.70 mm. Each packet usually has 22 to 25 eggs, but could have anywhere from 5 to 60 eggs. As the layings near an end, the number of eggs per clutch can decrease to 3 or 4, or even single eggs (Livezey and Wright 1947).
Larva: The tadpole is about 45 mm long, full and deep-bodied, and has a fairly long tail, about 2 times the head and body length. The labial tooth row formula is 2/3, and the spiracle is sinistral, directed posteriorly (Grismer 2002).
The general color is blackish and yellowish brown to dark brown with heavy black spots. Below, it is whitish with bronze or copper tinges. The tail is mottled with black, and the iris is golden, with a darker area anterior and posterior to the pupil (Stebbins 1951).
Call: H. regilla is the most commonly heard frog species on the Pacific coast. The calls last for about 1 second and are often uttered in sequence. Each 1-second call consists of a loud, two-parted 'kreck-ek', with rising inflection in the last syllable. H. regilla has a round vocal sac (Stebbins 1985).
While singing, a male may float with his limbs outstretched and his globular pouch extended to or beyond his chin (Stebbins 1951).
Food: H. regilla eats insects, including leaf-hoppers, spring-tails, flies, stoneflies, ants, wasps, beetles, and caterpillars, It also eats spiders, isopods, and snails (Stebbins 1972).
Behavior: H. regilla is mainly nocturnal, but it is also active in the daytime. Sometimes, at low elevations, it is active throughout the year. It is a good climber, but usually stays near the ground. It has a great capacity for color change, and a change from an unspotted dark coloration through a medium light colored phase with spots to an unspotted light phase may take about 8 to 10 minutes (Stebbins 1951).
A similar species, Hyla cadaverina, the California Treefrog, usually does not have an eye-stripe, has larger toe pads, and more fully webbed hind toes. H. cadaverina is also rarely green. Another similar species, Hyla eximia, the Mountain Treefrog, the eye-stripe extends beyond the shoulder and webbing is reduced (Stebbins 1985).
It is certain that there are isolated populations of H. regilla in many unexplored canyons of the Sierra la Giganta that harbor hidden permanent springs. In some water systems west of San Ignacio, there is evidence that H. regilla is being displaced by the bullfrog, Rana catesbeiana (Grismer 2002).
See another account at californiaherps.com.
Grismer, L. L. (2002). Amphibians and Reptiles of Baja California. University of California Press, Berkeley.
Livezey, R. L., and Wright, A. H. (1947). ''A synoptic key to the salientian eggs of the United States.'' American Midland Naturalist, 37, 179-222.
Smith, R.E. (1940). ''Mating and oviposition in the Pacific Coast tree toad.'' Science, 92(2391), 379-380.
Stebbins, R. C. (1972). Amphibians and Reptiles of California. University of California Press, Berkeley, Los Angeles, London.
Stebbins, R. C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.
Stebbins, R.C. (1951). Amphibians of Western North America. University of California Press, Berkeley.
Written by Sunny Shah (sunnys AT uclink.berkeley.edu), AmphibiaWeb
First submitted 2001-05-09
Edited by Tate Tunstall (2016-02-01)
Species Account Citation: AmphibiaWeb 2016 Hyliola regilla: Pacific Treefrog <http://amphibiaweb.org/species/929> University of California, Berkeley, CA, USA. Accessed May 25, 2019.
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Citation: AmphibiaWeb. 2019. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 25 May 2019.
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