© 2002 Brad Moon (1 of 38)
Can you confirm these amateur observations of Hyla gratiosa?
Hyla gratiosa LeConte, 1857
Joseph C. Mitchell1
1. Historical versus Current Distribution. The historical distribution of barking treefrogs (Hyla gratiosa) was probably more widespread than is currently known. Disjunct populations in Kentucky and Tennessee, and in Maryland, Delaware, and southern New Jersey in the Atlantic Coastal Plain (Black and Gosner, 1958; Monroe and Giannini, 1977; Anderson and Dowling, 1982; Caldwell, 1982b; Arndt and White, 1988; Redmond and Scott, 1996) suggest that this species was once more widespread than it is today. Barking treefrogs currently occur in the Coastal Plain of the southeastern United States from southern New Jersey and Delaware, through southeastern Virginia, south through most of the Florida Peninsula, and westward to southeastern Louisiana (Caldwell, 1982b). Populations occur in the Piedmont of Alabama and parts of Georgia and South Carolina. Barking treefrogs are absent from most of the Atlantic Coastal Barrier Islands (Caldwell, 1982b).
2. Historical versus Current Abundance. Historical abundance is unknown. Estimates of current abundance range from common in North Carolina, Florida, and Louisiana, to uncommon to rare in Kentucky, Tennessee, Virginia, and northern states. Barking treefrogs are not often encountered except after hard rains (Neill, 1958b). VanNorman and Scott (1987) reported an average of 3.3 calling males/site in Kentucky and Tennessee, but numbers of 130 males or more have been observed at breeding sites in other parts of the range of this species (Goin, 1938; personal observations). Murphy et al. (1993) reported a census population size of 1,082 adults for a site in Florida.
3. Life History Features. Aspects of the life history and biology of these treefrogs have been summarized by Wright (1932), Wright and Wright (1949), Murphy et al. (1993), and Murphy (1994a,b).
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Adults migrate from arboreal and terrestrial retreats to breeding sites. Mass migrations have not been reported. Neill (1958b) and Murphy (1994a) reported males entering ponds along the ground and by jumping into the water from tree branches overhanging the water.
ii. Breeding habitat. Barking treefrogs breed in a wide variety of shallow wetlands, including ephemeral pools, semi-permanent ponds, and permanent ponds. Observed habitats include corn fields, cypress ponds, acid bogs, flooded ditches, swamps, flooded sand pits, woodland ponds, sinkhole ponds, Carolina bays, live oak hammock wetlands, human impoundments surrounded by fields, and backwaters of streams (see summaries in Wright and Wright, 1949; Mount, 1975; VanNorman and Scott, 1987). Most populations occur in wetlands with aquatic vegetation. Wetlands with fish are seldom used for breeding.
The breeding period occurs from mid June to late July in Kentucky (VanNorman and Scott, 1987); late April to July in Alabama and North Carolina (Mount, 1975; personal observations); mid March to mid August in Louisiana (Dundee and Rossman, 1989); and March–August in Florida (Murphy, 1994a). Initial dates of calling vary due to temperature and dry versus wet conditions; calling dates were 25 May–18 June in one North Carolina population (Travis, 1983b). Males call from perches on vegetation in and out of the water, but primarily while floating on the water's surface. Neill (1958b) described the barking call given from arboreal perches during the day and the breeding call produced when calling from water. Carr (1940a) noted that the barking call was heard in Florida from 1 March–23 October. In Florida, breeding is sporadic until mid April after which it is nearly continuous with females mating on 72–95% of the nights during this period (Murphy, 1994a). Most males are present for ≤ 8 nights at a breeding site, but some are present for as many as 26–46 nights (Murphy, 1994b). However, Travis (1983b) stated that nearly all eggs are laid on two nights in North Carolina. Brandt (1936a) noted egg laying as late as 7 August in North Carolina. Females select males in vegetation and in water, and ovulation occurs only after amplexus is initiated (Fortman and Altig, 1973). Amplexus lasts from 5 hr to all night and females move around the pond while depositing eggs (Travis, 1983b; Murphy, 1994b). Both sexes move to the surrounding vegetation after mating. Females are not known to produce > 1 clutch/yr. Amplexus, or a cue associated with amplexus, triggers oviposition (Scarlata and Murphy, 2003).
i. Egg deposition sites. Females deposit eggs singly on the substrate of the breeding pond (Livezey and Wright, 1947; Travis, 1983b).
ii. Clutch size. Females lay about 1,500–4,000 eggs (Livezey and Wright, 1947; Travis, 1983b). Number of eggs laid is positively correlated with time spent in amplexus (Scarlata and Murphy, 2003).
C. Larvae/Metamorphosis. The large and uniquely shaped tadpoles develop in 41–160 d (Wright, 1932; Travis, 1984; Dundee and Rossman, 1989) and metamorphose in June–August, depending on latitude, pond hydrology, and temperature. Tadpole densities reach 4–8/m2 in some ponds (Caldwell et al., 1980). Survivorship in field enclosures was 0.1–0.22 and varied due to invertebrate densities (Travis, 1983a). Size at metamorphosis is 18–28 mm SVL and is affected by food availability, genetic relationships, and temperature (Travis, 1980a,b; Dundee and Rossman, 1989; Leips and Travis, 1994).
D. Juvenile Habitat. Juveniles remain in low vegetation following metamorphosis, sometimes dispersing widely from natal ponds.
E. Adult Habitat. Adult barking treefrogs remain in trees and shrubs or burrow into damp sand under logs or grass tussocks around the pond border when they are not engaged in calling or reproduction in water (Neill, 1952, 1958b). Neill (1952) found them no more than 1.5 m above ground on vegetation, but I have seen them about 2.5 above ground on tree limbs. Murphy (1994a) reported movements of 100 m between breeding ponds by several males in Florida.
F. Home Range Size. Home range size is unknown.
G. Territories. Barking treefrogs do not maintain or defend territories.
H. Aestivation/Avoiding Dessication. Aestivation occurs during dry periods in summer. Neill (1952) noted that barking treefrogs aestivate in sandy soil beneath grass tussocks.
I. Seasonal Migrations. Barking treefrogs do not migrate seasonally, but remain in the vicinity of breeding sites.
J. Torpor (Hibernation). Barking treefrogs burrow into sandy substrates in Georgia and Florida and use gopher tortoise (Gopherus polyphemus) burrows and other burrows for overwintering, although Neill (1952) suggested that they may dig backwards similar to toads to create their own subterranean retreats. Carr (1940a) found adults 1.2 m below the surface. Lee (1968b) found adults in Florida gopher mouse (Peromyscus floridanus) burrows.
K. Interspecific Associations/Exclusions. This species occurs with other frogs that use shallow wetlands for breeding, including northern cricket frogs (Acris crepitans), southern cricket frogs (Acris gryllus), Fowler's toads (Bufo fowleri), southern toads (Bufo terrestris), narrow-mouthed toads (Gastrophryne carolinensis), Cope's gray treefrogs (Hyla chrysoscelis), eastern gray treefrogs (Hyla versicolor), green treefrogs (Hyla cinerea), pine woods treefrogs (Hyla femoralis), squirrel treefrogs (Hyla squirella), Brimley's chorus frogs (Pseudacris brimleyi), spring peepers (Pseudacris crucifer), upland chorus frogs (Pseudacris feriarum), American bullfrogs (Rana catesbeiana), green frogs (Rana clamitans), and southern leopard frogs (Rana sphenocephala; de Rageot, 1969; VanNorman and Scott, 1987; personal observations). Syntopic salamanders include Mabee's salamanders (Ambystoma mabeei), mole salamanders (Ambystoma talpoideum), tiger salamanders (Ambystoma tigrinum), and eastern newts (Notophthalmus viridescens).
Mecham (1960b), Gerhardt et al. (1980), and Lamb and Avise (1986, 1987) evaluated hybridization between barking treefrogs and green treefrogs in Alabama and Georgia.
L. Age/Size at Reproductive Maturity. Age at sexual maturity is unknown for barking treefrogs. VanNorman and Scott (1987) reported that the smallest adult male was 45 mm SVL; the smallest adult female 57 mm.
M. Longevity. Maximum known longevity for a captive adult was 10 yr, 3 mo (Snider and Bowler, 1992).
N. Feeding Behavior. These gape-limited predators eat anything that they can swallow. Murphy et al. (1993) found that prey in 30 adult males represented nine orders from three classes of arthropods, with the majority being insects and beetles (Coleoptera) being the most common insect taxa. Barking treefrogs are opportunistic foragers, consuming arboreal and terrestrial prey.
O. Predators. Known predators of barking treefrogs are dragonfly naiads, mole salamanders (Ambystoma talpoideum), banded water snakes (Nerodia fasciata), cottonmouths (Agkistrodon piscivorus), and southern hog-nosed snakes (Heterodon simus; Neill, 1952; E.E. Brown, 1979; Caldwell et al., 1980).
P. Anti-Predator Mechanisms. Adults inflate with air when disturbed but are not known to be toxic. Small tadpoles have a black saddle in the middle of the tail musculature (Altig, 1972b) that may direct predators away from the body. Caldwell et al. (1980) found that tadpoles showed an average immobile response time of > 4 min when predation was simulated. When frightened or prodded, tadpoles initially dart off, then sink slowly a short distance as they become immobile (Caldwell et al., 1980).
Q. Diseases. None reported, although Mitchell and Green (2003) recently documented an intestinal hernia representing a developmental malformation.
R. Parasites. None reported.
4. Conservation. Barking treefrogs are locally common throughout much of their range from North Carolina southward. However, this species is listed as state Endangered in Delaware, Threatened in Virginia, and legally Protected in Maryland and Tennessee (Levell, 1997). Disjunct populations in Kentucky are not protected. Habitat loss and the small number of occurrences contribute to their protected status in the northern portions of their range.
Murphy et al. (1993) made three management recommendations for a location in central Florida: (1) decisions on this species should be based on estimates of effective population size and not short-term census results; (2) multiple ponds in the landscape should be protected because barking treefrogs migrate among breeding sites; and (3) habitats between breeding ponds should be protected to allow dispersal. Similar recommendations would be appropriate for other areas where barking treefrogs breed in complexes of ponds.
1Joseph C. Mitchell
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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