Northern Red-legged Frog (Rana aurora)

Frogs on the move!

Frogs on the move!

A frog of the forests west of the Cascades, northern red-leggeds occur up to 4,000 foot in elevation, and prefer moist coniferous or deciduous woodlands and forested wetlands with access to breeding sites. A mature female is about 4 inches long, the male 3 inches.  Their coloring ranges from rich brownish red to sandy brown, or the colorations of wet, fallen leaves; the red-brown of big leaf maple to the buff of Oregon oak. Their eyes are golden, and their backs may be unmarked or with black speckling or irregular black marks.  The underside of their hind legs is a translucent red; aurora is Latin for dawn, and probably refers to the red, pink or orange on the legs, like the sky at dawn.  Red-leggeds have dorsolateral folds (ridges running down both sides from behind the eyes to the hips.)

When the forest is wet they may roam far from standing or flowing water, sheltering under sword ferns, in duff, and under woody debris.  During the dry summer froglets and adults live along streams, in moist sedge and brush, on shaded pond edges, and within stream banks and moist debris.  They are active both day and night, depending on the temperature.  When it’s wet they are more likely to be active at night.  Adults feed on insects, small snails, crustaceans, worms, tadpoles, small fish, even frogs of other species. 

Northern red-leggeds breed in cool, usually sunny to partly sunny ponds or lake edges, beaver ponds or slow streams, 1 1/2 to 6 feet deep. They like a thickly vegetated shoreline; a pond with dense overhanging willow on some edges and an intermix of native emergent aquatic plants which they attached their egg masses to.  Red-leggeds migrate to the breeding pond as early as October and as late as February depending on latitude. The latest research shows that these frogs can travel up to 2-5 km to get to breeding sites if necessary.  Males arrive first and defend a territory, remaining longer than the females.  Their advertisement call is a weak stuttering “uh-uh-uh-uh” under water, which the female must be close by to hear.  (The male also makes soft “chuckles” from terrestrial sites, and when these frogs are grabbed by some predator, like a Garter Snake, they sometimes produce a loud, startling “scream.”  To hear a recording of their The female produces 200 to 1100 eggs a season, the soft grapefruit to cantaloupe sized egg mass attached to a branch, stem, or bottom vegetation, typically at the surface or up to 8 inches below the water’s surface.  Masses may be close together and are sometimes found in clusters on the same plant or willow stem, but are usually not laid on top of each other.  As the eggs develop and just prior to hatching, the egg mass spreads out and has a frothy and sometimes green appearance, which is algae that collects in the mass and which the larvae feed on. 

The eggs hatch in 35 to 39 days, and the hatchlings cling to the egg mass or nearby vegetation by using their sticky adhesive glands (just like velcro!).  Tadpoles move to warmer parts of the pond, are dark in color and become golden as they approach metamorphosis.  From tadpole to metamorphosis takes about 80 days.  Vernal ponds must stay wet at least through July to support metamorphism in low elevations, later in high.  The juvenile frogs will remain around the pond for a year, even two, before migrating to the forest with the adults at the end of breeding season.  They can be found in road puddles, ditches and other bits of moisture and standing water, which may be important features for dispersing individuals. They reach sexual maturity in 3 to 4 years and live 8 to 10.

Northern red-legged frogs are listed as Sensitive-vulnerable by the State of Oregon, and are Endangered in California due to few breeding populations remaining, or of special concern, depending on which agency is consulted.  Threats include habitat loss and alteration, introduced fishes and bullfrogs, endocrine disruptors, nitrogen compounds and toxicants, and with increased urbanity, road mortality.

Pacific Treefrog (Pseudacris regilla)

Also known as the Pacific chorus frog, the Pacific treefrog is the smallest, most varied in color, and most common frog in Oregon and Washington.  3/4 to 2 inches long, their coloration may be green, tan, reddish, gray, brown, cream or black (and very rarely, blue), though most are green or brown, with pale or white bellies.  The males are smaller than the females, with a vocal sac on their throats which balloons when they call, and is noticeably darker than the female's light throat.  This frog has a black stripe, or mask, running from the snout through the eyes to the shoulders.  They can be distinguished from juvenile red-legged frogs (which are of similar size) by the treefrog’s toe pads and lack of a dorsolateral fold. Pacific treefrogs are found from sea level to over 10,000 feet, in riparian habitat and woodlands, grassland, chaparral, pasture and urban areas, including backyard ponds.  They range through Oregon and Washington, into Idaho, and from extreme Northern California well up into British Columbia. 

The Pacific treefrog’s breeding call, a loud “ribbit,” or as the Chinookan people of the lower Columbia River had it, “Xwadet, xwadet,” is famous, as recordings of it have been used by Hollywood in jungle scenes for decades.  Mating takes place from early winter to early spring.  Studies have shown that one male acts as chorus master, initiating the calling.  Each male claims a territory and will butt and wrestle with other males who trespass.  Nearby males avoid overlapping with each others' calls to better their chances of mating.  Up to three males can time their calls so there isn’t overlapping.  Besides their advertising call males have an encounter trill call to warn off other males, and a “dry land call,” a long “cre-ee-ee-eeek,” that can be heard any time of year, except when it’s very dry or cold.

The breeding season for chorus frogs typically starts in February when the males move first to the breeding ponds to establish territories.  The females move a little later in February and early March.  Egg masses are usually found from mid-March through April.  When a male’s singing lures a female into the water he mounts her back in a posture called amplexus.  She moves out into the pond with the male on her back and releases the eggs while he fertilizes them, squeezing her to help thrust out the eggs.  (The breeding pond can be a chaotic place, with males attempting mating with non-vocalizing males, even salamanders!)  The female releases 400 to 750 eggs in small clumps of 10 to 90 each in shallow, calm water, attaching the masses to sticks, stems and grasses.  In two to three weeks the eggs go through their hatchling phase, becoming tadpoles, which seek out the warmest part of the pond.  The tadpoles feed on periplyton (a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus), filamentous algae, diatoms and pollen.

The tadpoles must contend with many predators in the pond, like the giant water bug, garter snakes and fish.  Tadpoles can identify the chemical cues of different predators in the pond water and initiate defensive responses specific to each.  For instance, blue gills are a chasing predator, so if tadpoles detect the presence of bluegills they undergo a change to become faster swimmers.  Giant water bugs are sit and wait predators, so when the tadpole senses their presence they develop a longer tail, luring the beetle to attack the tail rather then their body, which gives the tadpole a better chance of escape.  The metamorphosis of the tadpole takes place after 2 to 2 1/2 months, though if the pond is drying metamorphosis can accelerate.  Metamorphosis is a perilous time for the youngster as it can’t swim as well as a tadpole, nor jump as well as a frog, so while it undergoes the change it’s more vulnerable to predators.    

Tree froglets mature quickly and are ready to mate after metamorphosis.  Pacific treefrogs may live up to 9 years in captivity, or 5 to 7 in the wild.  Adults eat spiders, insects, and arthropods, and can ingest creatures almost as large as they are, their bodies expanding to take in such meals. They are excellent climbers, with pads on the tips of their toes with which they cling to smooth surfaces, but despite their name, are mostly ground dwellers.  They have glands in their skin that produce a waxy coating that helps them stay moist, though when it’s hot or cold or dry they hide under moist debris or in animal burrows.  (They were one of the few animals able to survive the Mt St Helens eruption in 1980, that is, those that were under ground when the mountain blew.) Another survival adaptation is when exposed to bright light and high temperatures their coloring becomes much lighter, even bright yellow, so they are able to reflect solar radiation more effectively.  They can also lose spots when living in monochromatic surroundings, while retaining spots when living in a patterned background.  Pacific treefrogs are a keystone species, which is to say they’re important for other animals, like garter snakes.  So far Pacific treefrog populations remain stable.