_3_2jlXHL.webp)
Pseudacris regilla, the Pacific treefrog, lives along the Pacific coast of North America, from extreme southern Alaska and British Columbia through Washington, Oregon and Northern California. It is a small, slender frog, reaching up to about 50 mm (2 in) from snout to urostyle, with males typically smaller than females, and it ranks among the most familiar frogs of the West Coast thanks to its loud, far-carrying call.
Identification
The species shows striking colour variation, appearing green, tan, reddish, gray, brown, cream or black, though most individuals are some shade of green or brown with pale or white bellies. Its clearest field mark is a black or dark brown eye stripe that runs from the nose, across the eye and back to the shoulder. The skin is covered in small bumps rather than smooth, and each toe ends in a round, sticky toe pad used for climbing and clinging to surfaces, though the toes themselves are long and only very slightly webbed. Calling males can be told apart by a dark patch on the throat where the vocal sac inflates. The frog can also shift its dorsal colour over weeks to months, with the first changes visible within hours, a response to seasonal changes in background brightness rather than to the colour of its surroundings; a rare recessive blue morph has also been documented.
Habitat and range
Pseudacris regilla tolerates a very wide range of conditions, occupying riparian habitat, woodlands, grassland, chaparral, pasture land and even urban areas including backyard ponds. It breeds in aquatic sites but spends much of the year away from water, and turns up from sea level to over 10,000 feet.
Behaviour and breeding
Males advertise with a loud two-part “ribbit” or “crek-ek” call, and outside the breeding season they can also give a long “dry land call,” heard at almost any time of year except the coldest and driest spells. Breeding itself runs over an extended window, typically from December to May with some year-to-year variation. Females lay eggs in clumps of 10 to 90, attached on or under vegetation and leaf litter in the pond, and these hatch into tadpoles within one to three weeks. The tadpoles graze on periphyton, filamentous algae, diatoms and pollen, scraping it from surfaces with a beak-like mouth structure, and most complete metamorphosis about two to two and a half months after hatching, though some individuals take up to five months. Adults feed on spiders, beetles, flies, ants and other insects and arthropods, including prey nearly as large as themselves. Displaced frogs also show a homing ability: in one study, frogs moved 300 yards from their home pond were recaptured there at a rate of 66.3%, suggesting they navigate home using smell, hearing or a sense of body position.
Conservation
The IUCN category for the Pacific treefrog is given in the facts box above. The species is described as the most common frog on the West Coast of North America, with most populations appearing healthy, and it plays an outsized ecological role: it is considered a keystone species, with predators such as garter snakes depending on its abundance as prey, while its own eggs are preyed on by the rough-skinned newt and other amphibians. Washington State named it the official state amphibian in 2007.
Similar species
Pseudacris regilla was long classified as Hyla regilla before the genus was changed to Pseudacris in 1986. A molecular study in 2006 split what had been treated as one wide-ranging species into three: the northern Pseudacris regilla, the central Pseudacris sierra and the southern Pseudacris hypochondriaca, a revision that remains controversial among herpetologists. Because the three were only recently split and look very similar, range is usually the best way to tell them apart, along with the eye stripe and toe pads shared by the whole group.