Most frogs will try to flee and escape when captured; this is not the case with the river frog. Instead of trying to escape, the River Frog often will simply go limp and play dead. Another defense mechanism of this frog is to secrete a noxious and odorus substance onto its attacker (USGS 1999).
The tadpoles of the river frog are larger than those of most species, reaching a length of 4 inches before metamorphosis. The tadpoles also organize themselves into schools, which is not common among ranid frogs or among large tadpoles of any kind (Altig 1981). Schooling may be an anti-predator mechanism; i.e., safety in numbers (Bartlett and Bartlett 1999). Another proposed benefit is that schooling creates social facilitation among the tadpoles which is beneficial to their survival (Altig 1981).
The river frog is still common in areas of the southeastern United States that still have proper habitat. With the preservation of their habitat the river frog should have no problem persisting in the future (Bartlett and Bartlett 1999).
US Federal List: no special status
IUCN Red List of Threatened Species: least concern
Development - Life Cycle: metamorphosis
The river frog does not appear to present any negative attributes concerning the environment or humans.
The river frog are an important species for their aesthetic value, ecological importance, and the consumption of insects, some of which are considered to be pests by humans.
The river frog feeds largely on insects and other invertebrates; they occasionally take small vertebrate prey, such as other ranid frogs of suitable size.
The river frog can be found in the southeastern portion of the United States. It is found in parts of the following states: Mississippi, Alabama, Georgia, Florida, South Carolina and North Carolina (FCES 1999).
Biogeographic Regions: nearctic (Native )
The river frog is not limited to rivers as its name may imply. They can also be found in and along lakes, ponds, swamps, streams, and marshes. They prefer open, thinly vegetated shoreline habitats (Bartlett and Bartlett 1999).
Aquatic Biomes: lakes and ponds
The river frog ranges from 3.25 - 4.63 inches in snout-vent length (record length 6.13 inches). The dorsal surface of the frog is a greenish black color. A common field mark is the presence of light spots on the lips; these spots are usually larger on the lower jaw. The skin is more rugose than the skin of most other ranid frogs. The belly ranges from gray to almost black in color, and is marked with light spots or short wavy lines (Conant and Collins 1998). Males often have a yellowish suffusion on the throat. The river frog has no dorsolateral ridges as found in many other ranid frogs. The webbing on the hind feet extend to the last phalanx on the longest toe (Bartlett and Bartlett 1999). Tadpoles of the river frog are rather large, reaching 4 inches before metamorphosis. The tadpoles undergo ontogenetic color changes. Small tadpoles have well-defined light rings around the body, posterior to the eyes, these rings disappear with growth (Bartlett and Bartlett 1999).
Other Physical Features: ectothermic ; bilateral symmetry
Male river frogs call to attract local females from April into July. The call of larger more mature frogs is a deep, low pitched, roaring snore. Smaller males give off a much higher pitched call than do the larger males. The males will call while sitting in shallow water or on the shore near the waters edge (Bartlett and Bartlett 1999). When the male attracts a female they will go into amplexus. The male will use his enlarged thumbs to grasp the female while fertilizing the eggs as she deposits them (Wright 1932). The female will lay several thousand eggs that form into a surface film, often among emergent vegetation to which they adhere. The tadpoles overwinter and take about one year to metamorphose (Bartlett and Bartlett 1999).
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate)
The river frog (Lithobates heckscheri) is a species of aquatic frog in the family Ranidae. It is endemic to the southeastern United States. Its natural habitats are temperate rivers, swamps, freshwater lakes and freshwater marshes. It is threatened by habitat loss.
Historically, the river frog has been known as Rana heckscheri but was placed in the genus Lithobates by Frost et al., 2006, this being a separate genus of ranid frogs that included most of the North American frogs traditionally included in the genus Rana. This change has proved controversial, and some authorities treat Lithobates as a subgenus of Rana, with the river frog's scientific name being written Rana (Lithobates) heckscheri.[2]
The river frog is a very large species with adults commonly between 7 and 13 cm (3 and 5 in) in length. The skin is rough and wrinkled but there are no dorso-lateral ridges as there are in the green frog (Lithobates clamitans). The back is some shade of dark green or blackish-green and the belly is dark grey, or blackish with pale wavy lines and specks. A distinctive characteristic is white spots on the lips, particularly on the lower lip, and this helps to distinguish this species from bullfrogs (Rana catesbeiana) and pig frogs (Rana grylio). Another distinguishing feature is a pale band outlining the groin. Males have a yellowish throat and their tympani (eardrums) are larger than their eyes while those of females are smaller.[3]
The river frog is endemic to the Atlantic and Gulf coastal plains of the southeastern United States. Its range at least formerly extended southwards from the southern part of North Carolina to southeastern Mississippi and northern Florida; it is now thought to have been extirpated from North Carolina due to habitat loss.[4] Its typical habitat is marshes and other wet locations with emergent vegetation near streams, rivers, ponds and lakes.[1]
Adult river frogs have a home range of about 16 square metres (170 sq ft). They are largely nocturnal and feed on insects and other invertebrates, as well as small vertebrates, including frogs. They spend much of their time in water and are relatively bold. During hot weather they are normally found sitting in moist or wet places, presumably to avoid desiccation. When the temperature falls below about 17 °C (63 °F) they are no longer to be seen in their normal habitat and are likely to be seeking refuge from the cold under water.[2]
Breeding takes place between April and August with males calling from the edge of ponds and swamps from April to July. The call has been described as "a deep, low-pitched, rolling snore".[3] The eggs are laid in a floating layer among emergent vegetation, a clutch numbering several thousand eggs which hatch after about three days. The tadpoles are at first a dark color but become much paler over time with a dark edge to the tail fin. They congregate in the shallows in the daytime, sometimes in dense swarms, but move into deep water at night. They feed on both animal and vegetable matter. They remain as tadpoles for a long period, overwintering once or twice, and reaching a snout-to-vent length of 97 millimetres (3.8 in) or more. After metamorphosis, the newly emerged juveniles are 30 to 52 millimetres (1.2 to 2.0 in) long and move away from the margins of the water. The large number of juveniles compared to the relatively small number of adults indicates a high mortality rate for newly emerged young. Predators that feed on tadpoles and juveniles are thought to include the banded water snake (Nerodia fasciata), other water snakes (Nerodia sp.), the largemouth bass (Micropterus salmoides) and the grackle (Quiscalus sp.). However the skin may contain some noxious substances or malodorous secretions as some snakes, including the indigo snake (Drymarchon), have been observed gagging and retching after eating a river frog. Even after the frog has been regurgitated, the snake continued to wipe its mouth on the ground.[2]
The river frog has a wide range and is quite common in much of that range. The population appears to be large and reasonably stable and the main threat the frog faces is degradation of its habitat; it has declined in portions of its range due to this, and is thought to have been extirpated from the northernmost extremity of its range in southern North Carolina by 1975.[4] However, it is present in a number of protected areas and the IUCN considers its conservation status to be of "least concern".[1]
The river frog (Lithobates heckscheri) is a species of aquatic frog in the family Ranidae. It is endemic to the southeastern United States. Its natural habitats are temperate rivers, swamps, freshwater lakes and freshwater marshes. It is threatened by habitat loss.
