Pseudacris regilla
Northern Pacific Treefrog
(Also: Pacific Treefrog)

Pacific treefrogs (Pseudacris regilla) are common throughout North America, west of the Rocky Mountains. Their geographic range extends from southern British Columbia, Canada, south through Washington, Oregon, and California, to Baja California, Mexico. Their eastern-most portion of their geographic range extends into Nevada, Idaho, and Montana. Pacific treefrogs also have been reported in deserts of southern California, where they are thought to have been introduced. (Elliott, et al., 2009; Ripplinger and Wagner, 2004)

Pacific treefrogs occur in a variety of habitats, including mesic and xeric forests, high altitude mountains, and desert steppe. Most commonly, they occur in moist environments, especially in low vegetation near water. Typically, they are found near lakes, ponds, rivers and streams. They can also be found in residential areas. Outside of breeding season, they often are seen near large, which is thought to provide shelter from predators. Pacific treefrogs are tolerant of rapid changes in weather and varying climatic conditions. Populations extend across a broad elevational range, from sea level to nearly 3500 m; however, most populations occur around 914 m above seal level. (Jameson, 1966; Ripplinger and Wagner, 2004; Stebbins, 2003)

Pacific treefrogs are a small, slender frogs with large toe pads. They have smooth skin that varies in color from light-brown to bright-green. Pacific tree frogs with red or brown backs also have been reported, but are thought to be rare. This species typically has darker markings on its body, including stripes on its dorsal surface and sides of its heads, which vary in intensity and in some individuals may be nearly absent. A dark triangular marking between the eyes is also common. Generally, a line of broken spots extends down the ventral surface to the groin area. The legs, arms, and feet are generally darker than the rest of the body. Within their natural range, Pacific treefrogs are the only frogs with padded toes and dark markings. Pacific treefrogs can change their body color depending on environmental conditions and need for camouflage to avoid predation. Recent research suggests that P. regilla changes color seasonally to match the presence or lack of green foliage. Color variation has also been associated changes in mean temperature. At high temperatures, these frogs often turn a shade of yellow. Under cooler temperatures, they return to their more typical darker colors. Males often are slightly different in color than females. Their upper body can be a dark gray olive color and may have a brown band extending through the eye and a yellow stripe along the upper lip. Females may be similar to males in color, but with little to no yellow stripe on the groin. During breeding season, it is easier to distinguish males from females by their different colored throats. Females have a smooth white throat while males have a dark brown or yellow throat with wrinkled skin. (Awbrey, 1978; Bernard, 2005; Brattstrom and Warren, 1955; Holman, 2003; Morey, 1990; Stebbins, 1951; Stebbins, 2003; Wente and Phillips, 2005; Wright and Wright, 1949)

Adult body size in Pacific treefrogs ranges from 2.5 to 4.8 cm. Mature females tend to be larger than males, which is not uncommon for anurans. Body mass of newly hatched tadpoles is, on average, 0.24. After 30 days, weight increases to between 0.35 and 0.45 g, which is more typical of adult Pacific treefrogs. (Sparling and Fellers, 2009; Stebbins, 1951; Stebbins, 2003; Wright and Wright, 1949)

Pacific treefrogs, Sierran treefrogs, and Californian treefrogs were once considered a single species and referred to as Baja treefrogs (Pseudacris hypochondriaca). These species were later reclassified primarily due to differences in geographic ranges. These three species look very similar, except for the bumpy skin of the Sierran and Californian treefrogs. (Elliott, et al., 2009; Nussbaum, et al., 1983; Stebbins, 2003)

Breeding season for P. regilla extends from January to mid-May. During this time, females lay eggs which are brown and yellow. Males externally fertilize the eggs, which are usually laid in gently moving water, in clutches of 5 to 70 eggs, and must be kept moist. (Jameson, 1956; Wright and Wright, 1949)

Pacific treefrog tadpoles are of medium size, typically about 46.6 mm long, and brown in color. Tadpole tails are not flagellated. Pacific tree frogs show rapid growth during the first summer after hatching. Tadpoles undergo metamorphosis between 50 and 80 days of age. During the metamorphosis, individuals typically measure between 12 and 15 mm long. Within two months of metamorphosis, individuals approximately double in length. Newly metamorphosed frogs leave the breeding area and seek habitats similar to that of an adult frog. Pacific treefrogs reach sexual maturity quickly and participate in the first mating chorus following their hatching. (Jameson, 1956)

Breeding occurs seasonally for Pacific tree frogs and typically occurs from winter to spring. This species is polygynous. During the breeding season, males often are found near small bodies of waters, particularly ponds, where they begin to sing. Females are attracted to males based on their calls and their different colored throats. Females prefer males that initiate calling. Once attracted, females move towards males. Males continue calling for several minutes, followed by several minutes of silence. Males continues this pattern until females are in their immediate vicinity. (Dickerson, 1906; Whitney and Krebs, 1975)

Pseudacris regilla attracts mates using a choral song. Males call to females as loudly as possible and produce a croak so loud that they sound as though they are produced by multiple males. These sounds can be heard by numerous females. Once a female approaches, the male stops singing and attempts amplexus, a pseudocopulation act during which the male grasps the female with hist forelegs. Breeding takes place at night, near shallow water, typically after rainfall. Mating season usually extends from December to May, although some variation occurs. Altitude often affects the length of the breeding season. (Dickerson, 1906; Grinnell and Storer, 1924; Schaub and Larsen, Jr, 1978)

Male Pacific tree frogs are occasionally aggressive during breeding season. They produce a warning call if another male approaches too closely. If the intruding male does not leave the area, the two frogs may fight until one departs. In addition, while attracting females, males can extend vocal pouches on their lower jaw, which helps in calling females. The act of copulation takes place in water. They are oviparous, and once the female enters the water, the male grasps her and helps to thrust out the eggs as he fertilizes them. Eggs are laid in small ponds or puddles. Typical broods range from 5 to 70 eggs. A jelly-like substance is left with the eggs to maintain moisture. Eggs remain in shallow water, often near twigs or leaves. Once reproduction is complete, both the male and female leave the water. Eggs hatch in three to four weeks, and within three to seven days, offspring develop into tadpoles. Development time varies with the temperature of the environment. Once they emerge from the egg, offspring use the jelly-like substance carried with the egg to sustain them for the first two to three days. Tadpoles then swim to shallow waters and ingest nearly any edible food item. When tadpoles reach three months of age, they metamorphose into froglets. This typically occurs between July and September.Research shows that as water temperature increases, development time decreases. In general, Pacific treefrogs reach sexual maturity in 1 to 2 years. (Awbrey, 1978; Brenowitz and Rose, 1999; Dickerson, 1906; Goin, et al., 1978; Noble, 1931; Nussbaum, et al., 1983; Oliver, 1955; Pickwell, 1931; Pickwell, 1947; Schaub and Larsen, Jr, 1978)

Once females lay eggs in the water, both males and females abandon the eggs. There is no parental investment. (Goin, et al., 1978; Nussbaum, et al., 1983)

Little is known about the lifespan of Pacific treefrogs, either in the wild or in captivity. There is record of a captive Pacific treefrog that lived for 9 years. Other chorus frogs in the genus Pseudacris have an average lifespan of approximately 5 years in the wild. Closely related mountain chorus frogs P. brachyphona live for approximately 7 years in the wild. (Blaustein, et al., 2001; Green, 1938)

Pacific treefrogs are social, especially during mating season. Like other chorus frogs, Pacific treefrogs use calls to attract potential mates. Males avoid call overlapping, which helps to maximize each male's chances of mating. This pattern of call recognition suggests advanced social interactions. Pacific treefrogs remain dormant when temperatures are below 10 C. Above this temperature, they emerge from their dormant state and search for water. They prefer warm water and will not breed in or occupy areas near cool water. It has been reported that Pacific treefrogs are unable to call when their body temperature falls below 9.8 C or rises above 20 C. In addition, they do not lay eggs when water temperatures are below 12 C or above 15 C. Temperature also effects body coloration. At high temperatures, green and brown frogs turn a shade of yellow. Upon cooling, the frogs return to their typical coloration. (Awbrey, 1978; Brattstrom and Warren, 1955; Brenowitz and Rose, 1999; Jameson, 1956; Morey, 1990; Wright and Wright, 1949)

Pacific treefrogs show relatively unique behaviors when chorusing. They stop calling if they see an intruder, and then begin calling again after a few minutes. Chorusing continues unless the intruder moves again. On the other hand, vibrations, loud noises, and thrown objects do not interrupt chorusing. During the breeding season, males are territorial. They often produce warning calls to warn rival males to leave the area. If the intruding male does not leave, the two typically fight until one leaves the area. Because females are not attracted to encounter calls, these interactions may reduce mating success for males. (Awbrey, 1978; Brattstrom and Warren, 1955; Brenowitz and Rose, 1999; Jameson, 1956; Morey, 1990; Wright and Wright, 1949)

Limited information exists regarding the home range of Pseudacris regilla; however, it most often inhabits areas ranging from 60 to 300 m away from a suitable breeding areas. (Brattstrom and Warren, 1955; Morey, 1990)

Pacific treefrogs have a very rapid call that has been described as a “kreck-ek” noise. The rapid call is called the chorus note; this serves to bring individuals in the area together for breeding. Pacific treefrogs also have an encounter call that warns other males not to get too close during mating season. This differs from their normal call, which is lower pitched and longer. Research has shown that males avoid overlapping calls in order to increase each male’s chance to attract a mate. Typically, up to three males can call without overlapping, if timing is well synchronized. Pacific treefrogs have well developed senses of sight, smell, and hearing. Hearing is particularly well-developed, as these frogs must be able to call to each other during mating season. (Awbrey, 1978; Brenowitz and Rose, 1999; Wright and Wright, 1949)

As tadpoles, Pacific treefrongs consume a variety of aquatic invertebrates and detritus. They mostly feed on algae, bacteria, and floating vegetative debris. Adults primarily consume terrestrial invertebrates, with only 4.8% of their diet coming from aquatic sources. Adults usually feed at night on invertebrate species, often consuming great quantities of flying insects. During breeding season, adults may feed during the day. Adults capture insects by extending their tongues. The tongue is coated by a sticky secretion that traps the insect, along with any debris or dirt near the insect. Food items are typically swallowed whole. (Hothem, et al., 2009; Wright and Wright, 1949)

Garter snakes are known predators of Pacific treefrogs. Other predators include other species of frogs, raccoons, Virginia opossums, fish, and birds. Their primary defense against predators is to remain motionless, though this technique is only effective if the frog matches its environment very well. They also tend to hide in areas of tall grass or jump into water when threatened. The primary predator of Pacific treefrog tadpoles is mosquitofish. Research has shown that even when presented with mosquito larva, mosquitofish often prefer treefrog tadpoles. Other predators on tadpoles include numerous species of fish and some aquatic invertebrates. (Awbrey, 1978; Brattstrom and Warren, 1955; Goodsell and Kats, 1999; Morey, 1990; Wente and Phillips, 2005)

The best defense of Pacific treefrogs against predation is their camouflage. The coloration of their dorsal surface varies from shades of brown to shades of green. They tend to stay in habitats that have coloring similar to their bodies. Recent studies have shown that Pacific treefrogs can vary their coloring based on the presence or absence of green foliage. In addition, during spring and summer, when green foliage is abundant, these frogs tend to be greenish in color; in fall and winter, they tend to be shades of brown. (Awbrey, 1978; Brattstrom and Warren, 1955; Goodsell and Kats, 1999; Morey, 1990; Wente and Phillips, 2005)

Pacific treefrogs are insectivorous and may help control a number of insect pest species throught their geographic range. In addition, a number of different species depend on Pacific treefrogs as their primary prey. There is no information on the potential parasites of this species. (Goodsell and Kats, 1999; Watkins, 1996)

As an insectivore, Pseudacris regilla likely helps control insect pest species throughout their geographic range. (Bernard, 2005)

There are no known adverse effects of Pseudacris regilla on humans.

Pacific treefrogs are classified as a species of least concern on the IUCN's Red List of Threatened Species. They have a broad geographic range and are the most common frog in the United States, west of the Rocky Mountains. The greatest current threat to Pacific treefrogs appears to be increased predation from non-native mosquitofish; however, this threat does not occur throughout the entirety of the Pacific treefrogs geographic range. (Wright and Wright, 1949)