Other names: Northern Pacific Treefrog, Pacific Chorus Frog, Western Chorus Frog, Hyla regilla
The Pacific Treefrog is a relatively small species, growing up to 5 cm in length, with females typically growing larger than males. They are characterized by a black or dark brown mask that starts at the snout and runs horizontally through each eye ending at the shoulder, relatively long legs for their body size, and large, rounded toe-pads that make for efficient climbing. Pacific Treefrogs come in a wide range of colours including brown, tan, green, and in some cases, red, bronze, black, or even blue. Research has shown that Pacific Treefrogs are able to change their colour with the season to allow them blend in with the changing landscapes. The belly of Pacific Treefrogs is white or pale-yellow, and the throat of males is often light brown. Tadpoles have long tails with a large tail fin and are dull green to brown in colour, sometimes with gold speckling. In some regions, Pacific Treefrogs may be considered a keystone species as many other species, such as Gartersnakes, depend on Treefrogs as prey for their survival.
Pacific Treefrog Call
Pacific Treefrog calls are the classic “ribbit”, and because of this their calls are often used in Hollywood movies. Pacific Treefrogs call year-round, but are particularly noticeable in the spring when breeding occurs. A variety of different calls have been documented.
The Pacific Treefrog may be confused with the other species of treefrog in British Columbia, the Boreal Chorus Frog. The Pacific Treefrog can be distinguished from the Boreal Chorus Frog by its larger toe-pads, longer legs, and an eye stripe that ends at the shoulders as opposed to the groin. The two species can also be differentiated by location as their ranges do not overlap. The dark mask of the Pacific Treefrog can look like that of the Wood Frog, however, Wood Frogs lack toe pads and have distinct .
Credit: Dave Huth
Credit: J.N. Stuart
Boreal Chorus Frog
Credit: Dave Huth
In North America, the Pacific Treefrog is found all along the west coast, west of the Rocky Mountains, from British Columbia to Baja California. In Canada, Pacific Treefrogs are found in British Columbia where they are widespread and found across the southern interior, Lower Mainland, coastal regions, Vancouver Island and the Gulf Islands, and have been introduced to Haida Gwaii.
In Canada, Pacific Treefrogs are typically active from March through to October, and hibernate through the winter. They survive the frigid temperatures of winter by using a natural antifreeze, whereby they elevate their glucose levels to prevent their cells from freezing.
Pacific Treefrogs are found in a variety of ecosystems, from deserts to grasslands to rainforests, from sea level to more than 3300 m. During the breeding season in British Columbia, Pacific Treefrogs prefer aquatic habitats that are devoid of fish and are usually found in shallow and often temporary wetlands, pools, ponds, and slow-moving creeks. They can sometimes be found in garden ponds, roadside ditches, and flooded forest service roads. In the non-breeding season, they can be found in a wide variety of habitats including wetlands, meadows, open woodlands, grasslands, rocky cliffs, talus, and pastures. As their name implies, Pacific Treefrogs can be found foraging in trees and shrubs, although most individuals tend to forage on the ground.
During the breeding season in early spring, males call to attract females. Fertilization in Pacific Treefrogs occurs externally. Males grasp the females from behind and on top inand fertilizes small clusters of eggs attached to vegetation or leaf litter in shallow water. The female will lay up to 1,200 eggs in clusters of 5-120. The eggs are olive-brown on one side and yellow-cream on the other. Hatching occurs after approximately one month, and tadpoles undergo metamorphosis 2-3 months after hatching. Newly hatched frogs may be as small as 1 cm. Eggs and tadpoles often share ephemeral ponds with Long-toed Salamander larvae as temporary wetlands typically do not contain predatory fish and amphibians, such as American Bullfrogs, that require permanent water sources. Individuals reach sexual maturity the following year, and typically only mate once in their life, as they live to a maximum of three years, though they have lived up to 8 years in captivity.
Pacific Treefrogs are both diurnal (active during the day) and nocturnal (active at night), and forage in terrestrial habitats for invertebrates like flies, beetles, wasps, ants, mites, spiders, ticks, and snails. When adult Treefrogs sense a potential prey nearby, they commonly twitch a toe to attract it within easy reach of their tongues. Pacific Treefrog tadpoles feed in aquatic environments on algae and organic detritus.
Pacific Treefrogs are generally widespread and abundant and are thus not currently of conservation concern. The biggest threats to this species in Canada are habitat loss and degradation from logging and urban development. Pesticides/herbicides, agricultural effluent, road salt, and other contaminants can be detrimental to frog populations causing direct mortality and deformities. Pathogens such as Chytrid fungus and Ranavirus may also be threats to Pacific Treefrogs. Climate change may also pose a future threat to frog species in Canada, especially if the severity and frequency of drought events increase.
Did You Know?
Pacific Treefrogs have the ability to change colour from green to tan/brown to gray. It was previously thought that adults occurred as fixed colour variants, however, it has been shown that some individuals are able to change colours over the active season. They can also change from lighter to darker, from patterned markings to solid colours, and even display combinations of colours.
Colour change in Pacific Treefrogs appears to be triggered by a change in background brightness, rather than overall colour change in their environment. A full change in dorsal colouration takes from weeks to months, although the initial changes can be observed within a few hours. This ability likely allows Treefrogs to maintain their camouflage as seasons change and the overall environment changes from lush green foliage in the spring, to drier brown/gray litter in autumn.
Pacific Treefrogs appear to have a very good sense of direction, and often find their way back to their original pond. In one study, researchers moved frogs ~300 m from their pond and recaptured 66.3% of the frogs several days later in the original pond. The source of this homing instinct is still yet to be understood.