Northern Red-legged Frog

Contents:
 
Links:
Taxon, Status, and Ranks Habitat Photos
General Description State Status Comments
Identification Tips Inventory & Research Needs Key Features
Phenology Threats & Mgmt Concerns
Range References Distribution Map

Taxon, Status, and Rank

Species Rana aurora     Baird and Girard, 1852
Family Ranidae
(True Frogs)
Status none
State Rank S4
Global Rank G4

General Description

This is a medium-sized frog with a slender body, smooth skin, distinct dorsolateral folds, and an eye mask. Females can reach 106 mm snout-vent length and males 82 mm snout-vent length but in Washington females rarely exceed 90 mm and males rarely exceed 70 mm. The dorsal color is tan, brown or olive-brown with varying amounts of black spotting and speckling. The undersides of the legs and margins of the abdomen are brick to orange-red; a gray wash may also be present. A distinct, contrastingly mottled, patch of black and cream to greenish-yellow coloration is present at the juncture between body and legs on the side (the groin). The legs are long and webbing on the toes does not extend past the first joint on the longest toe. Juveniles resemble adults but may not have the red pigment on undersurfaces. Mature males have gray swollen pads, called nuptial pads, on the thumbs.

Larvae-The tadpole has an oval body with dorsal eyes. The tube for waste elimination (vent) is just right of the midline at the tail base, and the tube for moving respiratory water out of the body (spiracle) is on the upper middle left side. The dorsal fin terminates on the body at, or anterior to, the spiracle. The tail tip is pointed and the dorsal fin is at least as high as the height of the tail musculature. At hatching, the tadpoles are dark brown but appear black in most light. They have long tails and short gills. As the larvae grow, the gills become concealed, the body color and belly lighten and metallic flecks appear. In larger tadpoles, the ventral abdomen is often pinkish or yellowish and brassy flecks are visible on the sides. Tadpoles grow to 50 to 75 mm total length before metamorphosis.

Eggs –Egg masses are globular with jelly that is soft and pliable to the touch. Roughly the size of a grapefruit, they are attached to vegetation 15 cm or more below the water surface. Newly laid eggs appear black on top and white on the bottom. As the embryos develop, the jelly becomes looser and the egg mass tends to break free of its attachment, often flattening out and floating to the surface. Newly hatched tadpoles disperse from the egg mass soon after hatching.

Voice –The advertisement call is a weak, stuttering set of guttural notes (4-7) given on one pitch “uh-uh-uh-uh.” This call, produced primarily underwater, requires one to be close to the calling male to hear it. A chorus sounds like soft “clucking.” Individual males also produce infrequent low volume calls, “chuckles,” from terrestrial sites during the active season. The release call is “chuckling” accompanied by pulsing of the body. When grabbed by certain predators, such as Common Garter Snakes, Northern Red-legged Frogs release a loud and startling “scream.”

See Photos Page.

Identification Tips

Frogs - The presence of dorsolateral folds distinguishes all native True Frogs (ranid species) from other anurans in Washington State. All native True Frogs in western Washington are brownish colored frogs that are similar in general appearance. Cascades Frogs are easily distinguished by the honey-yellow coloration on the abdomen and undersides of the legs. The following Northern Red-legged Frog traits distinguish them from Oregon and Columbia Spotted Frogs: 1) the groin is mottled with black and greenish yellow or cream-colored blotches, 2) distinct dorsolateral folds are present along the entire dorsal margins, 3) the eyes are oriented outward (laterally) so that only a portion of the pupil is visible when the frog is viewed from above, and 4) webbing is reduced between the toes so that the webbing on the longest toe does not extend past the first joint and the webbing is concave when the toes are pulled apart. The exotic American Bullfrog and exotic American Green Frog have a distinct fold (supratympanic fold) from the posterior edge of the eye, around the top of the external ear (tympanum) and ending at the shoulder; and typically have green coloration on the head.

Larvae- Pacific Treefrog tadpoles differ in having eyes along the outline of the head when viewed from above. Western Toad tadpoles are black dorsally and ventrally,  have minimal if any metallic flecking, have flattened bodies, have a tail fin that does not extend onto the back, and have narrowly placed dorsal eyes on top of the head. Large American Bullfrog and American Green Frog tadpoles have distinct black spots on a khaki-colored body and the abdomen is an opaque yellow (intestines not visible) with no metallic pigment (Bullfrog) or with a coppery sheen (Green Frog). The tadpoles of the Northern Red-legged Frog, Oregon and Columbia Spotted frogs, and Cascades Frog are similar enough that distinguishing them in the field is challenging (see Recommended Field Guides and Keys on the Home Page).

Eggs – The Cascades Frog, Oregon Spotted Frog and Columbia Spotted Frog typically lay their eggs in communal clusters that consist of many (up to 60 or more) egg masses laid next to or on top of each other in shallow (less 15 cm) water and the eggs are not attached to sticks or vegetation. The Northwestern Salamander has a fist-sized globular egg mass that is solid to the touch, always attached to vegetation and the animal pole of the egg and the embryos are brown not black or dark brown.

See Key Features Page.

Phenology

Breeding in Thurston County, at 50-100 ft. (15-30 m) elevation, starts in late January or early February. Most eggs are laid within 2-3 weeks at each site, but a small percentage of populations, especially large ones, will continue to lay over a longer period of time. In southwestern British Columbia, eggs take approximately 3-5 weeks to hatch depending on when they are laid, water depth and water temperature. Oviposition appears to occur when surface water temperatures have reached 6° C. Most egg masses have hatched by late March in lowland areas. Tadpoles at low elevations start to transform in late June of their first year.

Range

In Washington, Northern Red-legged Frogs occur in the Pacific Coast, Puget Trough, North Cascades, West Cascades and East Cascades ecoregions. East of the Cascade crest, the only records from Kittitas and Yakima Counties are old museum specimen records. See Distribution Map.

For information on the complete range of this species, see NatureServe Explorer.

Habitat and Habits

Northern Red-legged Frogs are found in lowland (mostly below 3000 ft. [914 m] in Washington) moist forested habitats with access to suitable breeding sites. This species can persist in areas of low-density development and landscapes managed for timber. Transformed Northern Red-legged Frogs are the most terrestrial of our native True Frogs. It is not unusual to find them in moist forested habitats far from water bodies. However, most individuals are found in the vicinity of standing or flowing water, even during the non-breeding terrestrial phase of the seasonal life cycle. Juveniles have been found in road puddles in disturbed open habitats that would not typically be considered suitable habitat for the species. Puddles and other temporary sources of standing water may be important features for dispersing individuals.

Breeding habitats include a variety of still-water bodies that generally persist until at least July at low elevations, later at high elevations. Vegetation suitable for egg mass attachment must typically also be present. However, Northern Red-legged Frogs can sometimes lay eggs in mud puddles with no attachment brace but this pattern is infrequent. Larvae are grazers and can strongly influence the distribution of algae (periphyton) in some still-water habitats. In water bodies with introduced warm-water fish, egg masses are uncommon or absent suggesting that Northern Red-legged Frogs avoid these water bodies for egg laying.

Experimental studies have revealed that exotic warm-water fishes can interact with bullfrogs and other aquatic fauna in a manner that produces negative effects on Northern Red-legged Frogs. Overall, however, habitat structure and the presence of exotic fishes appear to be more important in determining the overall distribution and abundance of Northern Red-legged Frogs than simply the presence of American Bullfrogs.

The few data obtained on overwintering for Northern Red-legged Frogs in the Puget Lowlands of Washington have revealed that the species may overwinter in terrestrial habitat at least for part of the season. Overwintering data from the lower Columbia in Oregon indicate that frogs will shuttle between aquatic and terrestrial habitat depending on wintertime temperatures, moving into water when conditions are colder. Regardless of precise overwintering location, this species can remain active throughout the winter at low-elevation sites except when temperatures are near or below freezing. During periods of inactivity, Northern Red-legged Frogs have been found sheltering under or within sword fern fronds, the duff that accumulates below sword ferns, under woody debris and within stream banks.

Northern Red-legged Frogs can be active both day and night depending on temperature; during wet intervals, most activity takes place at night. They blend well into their surroundings and are difficult to detect unless they move. They are alert, fast frogs that will remain motionless when approached and then suddenly flee by leaping away with relatively long but evasive jumps.

State Status Comments

This is a common species that remains widespread throughout its historical habitat in western Washington. Declines in British Columbia, Oregon, and California cause concern. Breeding sites should be monitored regularly to make sure that populations are persisting even with substantial habitat loss across the Puget Trough; an area that covers roughly one-third of Northern Red Legged Frog range in Washington.

Inventory and Research Needs

Monitoring of populations is recommended, particularly in landscapes that are rapidly being urbanized as this species may be able to survive only in situations with intermediate levels of urbanization at best. Annual egg mass surveys to determine number of breeding females (one egg mass per adult female) is the most efficient method for monitoring populations of this species for long-term trend analyses. Early March is the best time to survey for egg masses of lowland populations.

Despite recent advances (see Current Research below), fully understanding the spatial scale at which this species operates both seasonal and inter-seasonally under different habitat conditions remains a significant knowledge gap in this species’ biology. More research in this area, and addressing overwintering patterns, is especially needed.

Current or Recent Research in Washington

Seven master’s theses addressing the Northern Red-legged Frog have been completely over the last 12 years. Theses have focused on habitat use patterns outside of the breeding site (Haggard 2000, Serra Shean 2002, Chan-McLeod 2003, Chan-McLeod and Wheeldon 2004, Schuett-Hames 2004), habitat partitioning where the species co-occurs with bullfrogs (Twedt 1993), the effects of invasive exotic plants on oviposition (Callison 2001), and evidence for endocrine disruptors (Bettaso and others 2002).

Current research using genetic data has resulted in a systematic revision of red-legged frogs (Shaffer et al. 2004) revealing that not only are Northern and California red-legged frogs valid species, but they are not closest relatives as previously thought. Apparently, Northern Red-legged Frogs are more closely related to Cascades Frogs than they are to California Red-legged Frogs. This has important implication to understanding the biology of Northern Red-legged Frogs and defining the status of the species within different states and provinces.

Threats and Management Concerns

Substantial recent declines have been documented for this species in other states. Reasons for the declines, other than habitat loss and alteration, have not been confirmed but have been attributed to impacts of introduced fishes, introduced Bullfrogs, hydrology, endocrine disruptors, nitrogen compounds, and toxicants. In some cases, as for UV radiation, experimental work found no mortality but negative sub-lethal effects may exist. Among the least studied threats, that is coupled with increased urbanization, is road mortality.

References

Adams (1999), Adams et al. (2003), Beasley (2002), Belden and Blaustein (2002), Bettaso et al. (2002), Brown (1975), Calef (1973a, 1973b), Callison (2001), Chan-McLeod (2003), Chan-McLeod and Wheeldon 2004, Dickman (1968), Dunlap (1955), Gregory (1979), Haggard 2000, Hallock and Leonard (1996), Hayes and Hayes (2003), Hayes and Jennings (1986), Kiesecker and Blaustein (1997, 1998), Leonard et al. (1997), Licht (1969a, 1969b, 1971, 1974, 1986), Marco et al. (1999), Nebeker and Schuytema (2000), Nussbaum et al. (1983), Ovaska (1997), Pearl et al. (2004, 2005a, 2005b), Richter and Azous (1995, 2001), Ritson and Hayes (2000), Schuett-Hames (2004), Schuytema and Nebeker (1996, 1998, 1999), Serra Shean (2002), Storm (1960), and Twedt 1993.

Personal Communications: Marc Hayes, Tuesday Serra Shean, Joanne Schuett-Hames


Hallock, L.A. and McAllister, K.R. 2009. Northern Red-legged Frog. Washington Herp Atlas. http://wdfw.wa.gov/conservation/herp_atlas/

Last updated: May 2009


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