The following account is modified from Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo (©2005 by the Regents of the University of California), used with permission of University of California Press. The book is available from UC Press.

Rana heckscheri Wright, 1924
River Frog

Brian P. Butterfield¹
Michael J. Lannoo²

1. Historical versus Current Distribution. River frogs (Rana heckscheri) were described by Wright (1924) and are found along the Atlantic and Gulf Coastal Plains from North Carolina south to the Oklawaha River, Florida, and west to the Mississippi River (Wright, 1932; Simmons and Hardy, 1959; Lodato, 1974; Martof et al., 1980; Conant and Collins, 1991; Bartlett and Bartlett, 1999a). Mount (1975) notes that river frogs are locally distributed. Hansen (1957) describes river frogs as "the least known ranid of the southeast." Beane (1998) failed to find any evidence of the existence of river frogs in North Carolina and stated that river frogs were last documented from the state in 1975. Additional range expansions or contractions have not been described.

2. Historical versus Current Abundance. Unknown. Both tadpoles and adults can be abundant. Wright and Wright (1949), quote Allen (1938): "Rana heckscheri is very common in the vicinity of Silver Springs, Florida, in the streams and rivers and in the lakes connected by streams which flow into the Oklawaha River." Can be common in appropriate habitats (Bartlett and Bartlett, 1999a). "In Alachua County, Florida, [tadpoles] transform consistently in April and May. H.K. Wallace and I found them emerging in tremendous numbers in a backwater of the Santa Fe River 1 May 1933; we probably could have collected a thousand with little difficulty. This disparity in relative abundance between the adults and the young of this species indicates an extremely low survival potential." (A.F. Carr, in Wright and Wright, 1949).

3. Life History Features.

A. Breeding. Reproduction is aquatic.

i. Breeding migrations. Adults breed in ponds with emergent vegetation (Martof et al., 1980; Bartlett and Bartlett, 1999a). Breeding begins in April and will continue when conditions are favorable, into August (Wright and Wright, 1949; Mount, 1975; Behler and King, 1998; see also Wright, 1932). In Florida, Carr (1940a) notes that river frogs begin breeding in April and will breed sporadically throughout the summer. Males can be heard calling from April–July (Ashton and Ashton, 1988). Separate tadpole size classes suggest multiple breeding events in particular wetlands (Wright and Wright, 1949).

ii. Breeding habitat. In habitats ranging from river edges to adjacent, upland ponds.

B. Eggs.

i. Egg deposition sites. Eggs are laid in a surface film in ponds near rivers and streams (Wright and Wright, 1949; Martof et al., 1980; Bartlett and Bartlett, 1999a).

ii. Clutch size. Three amplectic pairs laid an estimated 5,000 eggs (Allen, 1938). Based on counts of ova, Wright (1932) estimates clutch sizes between 6,000 and 8,000. Egg diameter 1.5–2.0 mm (vitellus; Wright, 1932). Ashton and Ashton (1988) report eggs hatch about 3 d after being laid, while Allen (1938) reports eggs hatching in 10–15 d.

C. Larvae/Metamorphosis.

i. Length of larval stage. Tadpoles will overwinter for 1 yr, perhaps 2 yr (Allen, 1938; Wright and Wright, 1949; Mount, 1975; Ashton and Ashton, 1988). Tadpoles reach a length (SVL) of 97 mm (Wright, 1932; Wright and Wright, 1949; Martof et al., 1980), 160 mm TL (Wright and Wright, 1949; Mount, 1975).

ii. Larval requirements.

a. Food. Wright and Wright (1949) note that tadpoles not only fed on meat thrown into a lake to feed the alligators, but also on plant material. Feeding activity of schooling tadpoles can be stimulated by a single tadpole, even in the absence of olfactory stimuli (Altig and Christensen, 1981; see also Punzo, 1991b).

b. Cover. Tadpoles tend to aggregate in shallows during the day but return to deeper water at night (Wright and Wright, 1949). Tadpoles school in masses ("as no other big tadpoles do;" Wright and Wright, 1949) that can contain thousands of individuals (Altig and Christiansen, 1981; Ashton and Ashton, 1988). Wright (1932) notes "seething masses" of river frog tadpoles. Archie Carr, in Wright and Wright (1949), notes: "The number of tadpoles produced in a given breeding site is astounding." Schooling is unusual among ranids (Altig and Christiansen, 1981). It remains unclear whether schooling serves as an anti-predator device or serves some other, as yet unknown, function (Altig and Christiansen, 1981).

iii. Larval polymorphisms. Larvae change color from small, dark tadpoles to large, light tadpoles with a dark-edged tailfin (Allen, 1938; Wright and Wright, 1949; Bartlett and Bartlett, 1999a). Wright (1932) notes: "No other tadpole is so distinctive in the eastern United States."

iv. Features of metamorphosis. Newly metamorphosed animals are 30–52 mm long (Simmons and Hardy, 1959; Martof et al., 1980). In Alachua County, Florida, they transform consistently in April–May. River frogs will sometimes transform en masse, with metamorphosis at a single site lasting 2–3 wk. But Ashton and Ashton (1988) note that due to prolonged breeding and the requirement for a 1-yr developmental period, newly metamorphosed frogs can be observed throughout much of the year. Allen (1938) notes a 20% mortality at metamorphosis.

v. Post-metamorphic migrations. Long migrations are unlikely. Allen (1938) reports a juvenile found about 100 m from its water body, 1–2 mo after metamorphosing.

D. Juvenile Habitat. Appears to be more variable than adult habitats. Hansen (1957) notes that juveniles move greater distances than adults, in large part because adults confine their movements to a home range. Allen (1938) found that for several months after metamorphosis, no juveniles were found around the margins of their water body.

E. Adult Habitat. "Swampy edges of rivers and streams, a truly fluvatile species" (Wright, 1932). Nocturnal, terrestrial, associated with emergent vegetation (Wright, 1932; Wright and Wright, 1949; Behler and King, 1998). Can be found at night in shrubbery and the bases of trees along banks (Wright and Wright, 1949); Hansen (1957) notes an association with Sphagnum sp. In Alabama, Mount (1975) notes that river frogs also occur along the edges of shallow impoundments, such as beaver ponds, associated with vegetation such as titi, bay, and cypress. Nocturnal. Inhabit river swamps and swampy shores of ponds. Bottom land forests (Martof, 1980). Hansen (1957) notes that river frogs actively seek temperatures around 25 °C. Adults are not wary (Conant and Collins, 1991).

F. Home Range Size. Hansen (1957) calculated home range sizes for nine animals, a mean of 16 m2, and notes that this estimate is similar to that calculated for green frogs (Rana clamitans; 18.6 m2) by Martof (1953).

G. Territories. Defended territories have not been reported.

H. Aestivation/Avoiding Dessication. Hansen (1957) notes that river frogs are usually found around water bodies and noted that the fact that animals are "consistently found seated upon moist or wet substrates suggests that this type of substrate is actively sought to prevent desiccation."

I. Seasonal Migrations. Undocumented.

J. Torpor (Hibernation). When temperatures fall below 17 ˚C, Hansen (1957) found that river frogs are never observed and suggested, by comparison with green frogs, that river frogs avoid cold by moving into bodies of water.

K. Interspecific Associations/Exclusions. Hansen (1957) notes the following species at his study ponds: green frogs (R. c. clamitans), southern leopard frogs (R. sphenocephala), green treefrogs (H. cinerea), and Florida cricket frogs (Acris gryllus dorsalis). Will breed in same wetlands as pig frogs (Rana grylio; Wright, 1932).

L. Age/Size at Reproductive Maturity. Males 82–131 mm; females 102–155 mm (Wright, 1932; Wright and Wright, 1949; Conant and Collins, 1991).

M. Longevity. Unknown.

N. Feeding Behavior. River frogs feed largely on invertebrates, especially insects. They will also take small vertebrates, including other ranid frogs (Hill, 2000).

O. Predators. Southern water snakes (Nerodea fasciata) feed on tadpoles (Wright, 1932; Allen, 1938; Wright and Wright, 1949). Hansen (1957) also noted an association between river frogs and water snakes (Nerodia sp.). Wright (1932) suggests largemouth bass (Micropterus salmoides) prey on tadpoles, and grackles (Quiscalus sp.) feed on newly transformed animals.

P. Anti-Predator Mechanisms. Passive, not easily alarmed nor evasive; clumsy in their escape (Wright, 1932; Carr, 1940a; Wright and Wright, 1949; Hansen, 1957; Conant and Collins, 1991). Can be caught by humans using just their bare hands. Behler and King (1998) note that adults may have toxic skin secretions because water snakes and indigo snakes (Drymarchon sp.) become violently ill after ingesting river frogs; after regurgitating the animal they continue to wipe their mouths on the ground. Schooling in tadpoles is associated with predator avoidance and location of food (Wassersug et al., 1981; see also Punzo, 1991b; Bartlett and Bartlett, 1999a). Large tadpoles and adults will produce noxious and odorous skin secretions (Bartlett and Bartlett, 1999a). Large size at metamorphosis and in adults must deter gape-limited predators.

Q. Diseases. Largely unknown. Punzo (1993) has, however, observed the effects sublethal concentration of mercuric chloride have on the ovaries of river frog females.

R. Parasites. Not well documented. A parasitic copepod (Argulus americanus) was found on a river frog tadpole (Goin and Ogren, 1956).

4. Conservation. River frogs are locally distributed and perhaps the least known ranid of the southeast. River frogs were last documented in North Carolina in 1975 (Beane, 1998), where they are considered a Species of Special Concern (Levell, 1997). Additional range expansions or contractions have not been described. According to Archie Carr (in Wright and Wright, 1949), the disparity in relative abundance between the adults and the young of this species indicates an extremely low survival potential.

¹Brian P. Butterfield
Department of Biology
Freed–Hardeman University
Henderson, Tennessee 38340-2399
bbutterfield@FHU.edu

²Michael J. Lannoo
Muncie Center for Medical Education
Indiana University School of Medicine
MT 201
Ball State University
Muncie, Indiana 47306
mlannoo@bsu.edu

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 19 Apr 2024.

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