Amphibians of North Carolina

Scientific Name:	Common Name:		Family (Alpha):

NC Records
Hylidae Members:
Hyla gratiosa - Barking Treefrog

Taxonomy

Class: Amphibia

Order: Anura

Family: Hylidae

Subfamily: Hylinae


Taxonomic Comments: Duellman et al. (2016) elected to split treefrogs in the genus Hyla into two genera. Hyla (sensu stricto) refers to a group of species that are found in Eurasia, while a new genus Dryophytes was resurrected to include all of the North and Central American species and three other species that are found in eastern temperate Asia. Members of these proposed genera cannot be distinguished by any known morphological features, but represent two clades. Whether members of these clades should be placed in separate genera or treated as lesser taxa such as subgenera is arbitrary and dependent on one's taxonomic philosophy. Here, we retain Hyla for North American species to be consistent with current usage by the Society for the Study of Amphibians and Reptiles.
Species Comments:

Identification

Description: Hyla gratiosa adults are large, robust treefrogs with granular skin and well-developed toe pads. The background color typically ranges from bright to olive green, but specimens are often seen that vary from grayish green to grayish brown or brown. The dorsal ground color on the head and body is usually evenly covered by darker spots that have lighter centers. These are roughly circular to oval in shape and can be inconspicuous or completely missing on some specimens -- particularly those that are very light or very dark (Beane et al. 2010, Dodd 2013). The upper surface of the legs has a series of dark bars or blotches, and the venter is unmarked and either whitish or with a yellowish wash that is concentrated near the bases of the legs and sides of the throat. There is a prominent white to yellowish-white stripe on each side that extends from the snout along the upper lip. From there it may extend along the side of the body as an irregular stripe all the way to the groin area, or become broken into a series of blotches and be much abbreviated. Smaller white stripes -- either complete or broken -- also occur on the outer margins of the forelimbs and the hind feet. The dorsum of the head, body, and legs are sometimes sprinkled with widely spaced yellowish flecks or tiny spots, but many specimens lack these. Individuals can change colors depending on temperature and the background upon which they are resting. Meshaka and Layne (2015) noted that populations in southern Florida are unusual in generally lacking the white striping that is seen on specimens elsewhere.

The males have dark throats during the breeding season, and differences in the average length of males and females appear to be slight. This is our largest treefrog, with the adults varying from around 50-70 mm SUL. The adults vary from 51-69 mm in the Carolinas and Virginia (Beane et al. 2010) and 50-70 mm in Georgia (Jensen et al. 2008).

Larvae that are less than 29 mm TL are translucent or whitish and have a very well-defined black saddle midway down the tail musculature (Dodd 2013). The saddle begins to disappear after reaching around 29 mm TL, and the larvae develop a translucent coloration with a dark lateral stripe. The older tadpoles have a wide, deep body and a wide dorsal fin that extends forward to the region of the eyes. Older larvae have a yellow preorbital stripe that extends from the eye to the tip of the snout, along with a pale postorbital stripe. The tail fin remains clear or becomes slightly speckled or blotched as the tadpoles grow larger (Dodd 2013).

Vocalizations: The males have two distinctive calls. One is the "tree call" that is issued from trees or bushes during the day and often following rains (Neill 1958, Wright 1932). It has been described by Neill (1958) as consisting of 9-10 raucous, repetitive barks ("uk-oh-oh-oh-oh-oh-oh-ohk-ohk-ohk") and is often made by males that are moving from the treetops to the breeding sites. The second call is an advertisement call that is usually given as males float in the water. It has been described as a hollow-sounding “bonk-bonk-bonk” or "moonk-moonk-moonk "and has also been compared to a dog barking. Of course, such comparisons have little value given the number of breeds and types of barks that dogs produce.

As with other treefrogs, calling is very energetically expensive and uses about 12X the energy compared to when an animal is resting (Prestwich et al. 1989). Under field conditions the advertisement call is repeated about once per second or slightly less. The repetitive calling can last for a few hours -- with occasional interruptions -- before the animals are exhausted. The hemispherical vocal sac acts to project sound effectively in all directions and the sound can be heard up to 2.5 km on a quiet night (Allen 1932, Dodd 2013). Males also have a release call that is given if a male attempts to amplex a second male.

Technical Reference: Dodd (2013)

Online Photos: Google iNaturalist

Observation Methods: Barking Treefrogs are most easily observed after dusk when they are at the breeding sites, particularly following afternoon thunderstorms or on warm, rainy nights. They can also be found crossing roads on rainy nights.

AmphibiaWeb Account

Distribution in North Carolina

Distribution Comments: The main range extends from portions of eastern North Carolina southward throughout the Coastal Plain and portions of the Piedmont to southern Florida, then westward to southern Mississippi and southeastern Louisiana. The range extends from the Gulf Coast northward though most of Alabama and Georgia to western and southern Tennessee. Major geographic isolates occur east of the Chesapeake Bay in Delaware, in southeastern and south-central Virginia, and in western Kentucky and a small adjoining area in Tennessee. In North Carolina, populations have been found in the southern three-fourths of the Coastal Plain and adjoining areas of the eastern Piedmont. We also have a few records from barrier islands off the coast.
Distribution Reference: Beane et al. (2010), Dodd (2013)
County Map: Clicking on a county returns the records for the species in that county.


GBIF Global Distribution

Key Habitat Requirements

Habitat: Hyla gratiosa is found in a variety of Coastal Plain and inland habitats, including mixed pine-deciduous forests, pine flatwoods, longleaf pine sandhills, xeric hammock, and basin and depression marshes (Dodd 2013). The adults primarily select fish-free temporary or semipermanent ponds for breeding. They can occasionally be found in permanent habitats with fishes, but typically restrict their breeding to shallow areas that have relatively few fish (Babbitt et al. 2006, Holbrook and Dorn 2015, Jensen et al. 2008). Some of the commonly used habitats include Carolina Bays, depression marshes, cypress savannas, cypress-gum ponds, as well as roadside ditches and flooded fields on occasion (Dodd 2013, Wright 1932).

Liner et al. (2008) surveyed a series of ponds in Georgia and documented the use of a wide variety of habitats that ranged from open, sunny marshes with a dense understory of grasses, to cypress/gum swamps with closed canopies and almost no understory or mid-story vegetation. Sites that were sunny or had relatively open canopies had higher use that closed-canopy sites. In southern Florida, Babbitt et al. (2006) found that the breeding sites are usually within 20 m of forests. VanNorman and Scott (1987) mostly found populations in limestone sink ponds in flooded grain fields in western Tennessee and adjoining areas of Kentucky, while Dodd (2013) noted that there is one anecdotal note of them using brackish water in Mississippi.

In North Carolina, the adults are arboreal and spend much of their time away from the breeding sites. They are perhaps most common seen in pine flatwoods or pine-scrub oak sandhills in the Coastal Plain. However, they also occur in the eastern Piedmont and a few populations have been reported on the barrier islands. Breeding sites typically consist of shallow, isolated, fish-free ponds, including swamps, ephemerally flooded depression ponds, borrow pits, and semipermanent Carolina Bays.

Environmental and Physiological Tolerances: This species appears to be less tolerant of low pH than some anurans. Delis (2001) found that the eggs cannot withstand a pH of <5.0.

Adaptations to Natural Disturbances: Most populations of this species appear to be associated with fire-maintained habitats in the Coastal Plain. Breeding adults may survive in ponds or wetlands, but away from these sites they probably escape surface fires by climbing up into the treetops or perhaps shallowly burrowing in sandy soils.

Biotic Relationships: The tadpoles are typically found in fish-free habitats and appear to lack chemical defenses against fishes and other aquatic predators such as Ambystoma larvae and odonates (Caldwell et al. 1980, Travis et al. 1985b). In general, mortality rates decrease as the tadpoles grow larger. The tadpoles decrease activity when exposed to potential predators -- particularly odonate larvae -- and to a lesser extent fishes (Richardson 2001). This presumably reduces encounter rates and the risk of predation. The tadpoles also probably reduce encounters with odonates by being mid-water feeders and having cryptic or disruptive coloration (Caldwell et al. 1980).

The juveniles and adults rely on cryptic coloration and immobility during the daytime to minimize predation risk. The natural predators are poorly documented, but likely include an array of species that are found at or near aquatic sites such as herons and egrets, aquatic and semiaquatic snakes (e.g., Murphy 1994b), and raccoons. Neill (1952) reported two instances of adults being preyed upon by the Southern Hognose Snake.

See also Habitat Account for Longleaf Pine Woodlands with Isolated Pools

Life History and Autecology

Breeding and Courtship: The breeding season based on calling males varies depending on geographic location. Populations in Florida breed from February-September. Breeding may extend into October in southern Florida and Louisiana (Babbitt and Tanner 2000, Dodd 2013, Krysko et al. 2019). Local and regional populations have more abbreviated calling seasons. Duellman and Schwartz (1958), for example, reported breeding from June-September in southern Florida, while Meshaka and Layne (2015) reported males calling from March-August at the Archbald Biological Station in south-central Florida. (Mount 1975) noted that most breeding in Alabama occurs from April-July, while VanNorman and Scott (1987) found that calling did not begin until May or June in western Tennessee and Kentucky depending on the year. Actually mating and egg laying is presumed to occur over a shorter period, with most occurring from mid-spring through mid-summer. In North Carolina, Travis (1983) observed calling males from 25 May–18 June in one population. Nearly all eggs were laid on a few nights, but the seasonal time of breeding varied among years. Brandt (1936) noted egg laying as late as 7 August in North Carolina.

Breeding in most populations tends to be erratic seasonally. In general, breeding tends to be most intense earlier in the season and on warm nights following moderate to heavy rains (Murphy 2003). The adults live in trees or woodland habitats that are close to the breeding sites and move to the ponds at night when the weather is favorable. After engaging in a breeding bout, the females presumably leave and move back to their home territories. The males stay longer at the ponds and either move back to woody vegetation in the immediate vicinity of the ponds after a night of calling, or seek cover in hiding spots such as damp sand under logs or the bases of grass tussocks near the pond margin (Neill 1958). They can sometimes be seen resting during the day on vegetation (Dodd 2013). Movement to and from the ponds occurs at night (Todd and Winne 2006), and calling usually begins with nightfall. The males typically call either while floating in the water, or less commonly while sitting on vegetation mats, logs or other substrates very close to the water surface (Murphy 1994a, Oldham and Gerhardt 1975, Wright 1932).

Calling is very energetically expensive and males loose weight during a calling bout. Murphy (1994a, b) conducted detailed studies of four populations in Florida and found that individual males only call for 1-4 hours each night. Most called for < 10 nights during the breeding season (median = 2-3 nights and 75% for < 8 nights) and the mating success of individuals was positively correlated with how many nights a male called. Males with relatively long chorus stays arrived in better condition, lost weight less rapidly, and ended their calling bout in poorer condition than males that stayed a shorter time. Calling is risky and as many as 20% of calling males succumbed to predation from snakes. About 16% of the males moved from one pond to another, and those that did added another 2.5 nights to the seasonal calling duration.

Murphy (1994a, b) found that the calling males are not territorial. The males rarely exhibit satellite behavior and do not try to dislodge nearby amplexed males. Females arrive at night after the males have been calling for a while. A choice experiment and field observations by Murphy and Gerhardt (2002) suggest that females that are moving to a breeding site first move to locations where they are able to detect the calls of several males simultaneously, then choose a mate among these at some distance from the males. Once a female picks a mate, she moves directly to him and initiates amplexus by nudging the male. The pairs stay amplexed for at least five hours before egg laying and fertilization occurs. Both sexes usually leave the pond and move back to woody cover immediately after mating.

Reproductive Mode: Dodd (2013) and Krysko et al. (2019) noted that the females lay their eggs in a continuous large monolayer or sheet on the water surface. However, Wright (1932) observed the eggs being deposited singly on the substrate or in small clumps that sink, so more observations are needed on egg deposition. Wright (1932) reported that the freshly laid eggs are light brown above and pale below and vary from 1-1-1.8 mm in diameter (mean = 1.4 mm). Each has a vitelline membrane and an outer envelope that varies from 2.3-5.0 mm in diameter (mean = 4.1 mm). The embryos typically develop to the hatching stages in 3-4 days and the hatchlings are 5.9–6.2 mm TL (Travis 1983).

A female is capable of laying over 4,000 eggs, but clutch sizes are more commonly about one-half this size. Reported clutch sizes include 557–4,034 eggs (mean = 1,990) in Florida specimens (Delis 2001), a mean of 1,991 eggs in additional Florida specimens (McCoy et al. 2021), and a mean of 2,728 eggs for Virginia specimens (Mitchell and Pague 2014). Perrill and Daniel (1983) documented once instance of a female laying two clutches 14 days apart.

Aquatic Life History: As with many other anurans that use seasonal ponds, the hatchlings grow rapidly. Their diet is poorly documented, but they tend to prefer midwater habitats during the day where they presumably filter-feed and escape predators below. As in many other anurans, growth rates, length of the larval period, and size at metamorphosis are dependent on environmental factors such as ambient temperatures (Blouin 1992a), food quality and quantity, larval crowding, and the types and densities of predators (Morin 1983). All else being equal, crowding generally tends to slow growth, lower survival, lengthen the larval period, and reduce the size at metamorphosis (Blouin 1992, Travis 1984, Wilbur 1982). Higher growth rates lead to shorter larval periods, which can allow larvae to metamorphose before ponds dry prematurely during dry years (Travis 1980, 1983). Although many seasonal pond amphibians respond to progressive pond drying by metamorphosing early, Leips et al. (2000) found that the experimental shortening of the hydroperiod had no effect on the length of the larval period of tadpoles in artificial communities.

The larvae can reach 50-71 mm TL when fully grown (Krysko et al. 2019, Jensen et al. 2008), however size at metamorphosis is highly plastic depending on site conditions. Estimating the length of the larval period in nature is difficult because egg laying is staggered seasonally and age cohorts are difficult to recognize. Wright (1932) estimated the larval stage to last around 41–65 days in Georgia, while tadpoles that Gunzburger (2007) placed in enclosures in natural ponds metamorphosed after 25-50 days on average depending on site and experimental conditions. Leips et al. (2000) had average larval periods of around 60 days for tadpoles grown in outdoor tanks. The average larval period in other experimental outdoor pools used by Pintar and Resetarits (2018) varied from around 59-81 days.

Wright (1932) found newly transformed individuals in Georgia that were 18–23 mm SUL, while Jensen et al. (2008) reported that metamorphs vary from 14-20 mm SUL. Individuals in experimental outdoor pools used by Pintar and Resetarits (2018) averaged from 16-18.5 SUL depending on the experimental conditions.

Terrestrial Life History: We know very little about the ecology of the metamorphs and young juveniles. The young juveniles presumably remain in vegetation and around pond margins for a few weeks after metamorphosing before moving away from their natal ponds. They disperse away from the breeding sites at night into nearby woodlands (Todd and Winne 2006). Studies of tagged adults suggest that the juveniles in some populations may move 200 meters or more from the breeding sites. Information on growth rates, survival, and age at sexual maturity is unknown. Based on information for other native hylids, the juveniles probably require 1-2 years to reach sexual maturity.

Delis et al. (2020) studied the movement of adults after they had finished breeding for the season. The adults made relatively short daily movements when dispersing away from a pond, with the mean daily movements varying from 0.4-17.2 m for different individuals. Individuals were relocated on the ground surface or in depressions for about 50% of the observations, while the remainder were on vegetation. The greatest total distance moved from the point of release was < 500 m (median = 221 m, range = 14–474 m), and most individuals moved up into the trees at the final locations and restricted further horizontal movement. In a similar study, Delis (2001) tracked adults in Florida and found that females moved an average of 122 m from the breeding sites (range = 9–289 m) versus 207 m (range = 38–330 m) for males. These observations and others made at the breeding sites suggest that males migrate moderately long distances to the breeding ponds at the start of the breeding season. They then remain in woods or brush adjoining the ponds and shuttle back and forth between the breeding site and adjoining trees to call nightly. Females presumably leave the sites after ovipositing and immediately return to their arboreal retreats. Todd and Winne (2006) found that almost all movements to and from the ponds occur at night.

Outside of the breeding season the adults tend to be strongly arboreal and shelter in dense vegetation. They can often be heard issuing tree calls from high in the canopy. During the day they commonly rest on vegetation with the limbs tucked into the body and the eyes closed (Dodd 2013), and are occasionally found resting around human dwellings. They use their limbs to coat themselves with a layer of mucous and lipids that retards water loss (Barbeau and Lillywhite 2005, Wygoda 1984). During cold winter weather or droughts individuals find shelter by burrowing a short distance into sandy soil (Neill 1952), or moving under downed logs, surface debris, tree holes, mammal burrows and other refuges (Dodd 2013, Franz 2005, Krysko et al. 2019). As with most frogs, this species is a gape-limited, opportunistic generalist that consumes a wide diversity of both arboreal and terrestrial prey. Insects comprising most of the diet, and beetles are particularly important (AmphibiaWeb 2022).

General Ecology

Population Ecology: We know very little about the population ecology of this species. Attempts to determine the sizes of local populations have been hampered by the fact that the adults regularly trespass over drift fences, and individual males tend to call for only a few days at a breeding site. As such, the number of calling males heard on a given night is presumably a gross underestimate of the population size. Many populations in the northernmost portions of the range appear to be small (e.g., VanNorman and Scott 1987), while many southern populations probably consist of hundreds of individuals. Adults are known to move between local breeding ponds, but it is uncertain to what extent populations show metapopulation organization or genetic connectivity at different spatial scales.

Community Ecology: Seasonal ponds in the Coastal Plain usually harbor diverse assemblages of both adult and larval amphibians and ecological interactions among community members are undoubtedly complex. Hyla gratiosa shares ponds with a wide array of species and its interactions with potential competitors and predators are poorly resolved. Morin (1983) manipulated the density of two predators (Notophthalmus viridescens; Ambystoma tigrinum) in artificial communities that had five species of anuran larvae (Scaphiopus holbrookii, Lithobates sphenocephalus, Anaxyrus terrestris, H. chrysoscelis, and H. gratiosa). Tiger Salamander larvae were highly effective predators that eliminated nearly all tadpoles from cattle tanks. In tanks without predators, H. gratiosa performed poorly and very few survived to metamorphosis, presumably due to competition with other community members. Hyla gratiosa performed best when there were moderate densities of newts in the tanks that removed many competitors.

Studies examining competitive interactions between H. gratiosa and H. femoralis in laboratory aquaria (Travis 1980, Wilbur 1982) or outdoor tanks (Warner et al. 1993) suggest that these species may compete in nature. Warner et al. (1993) found that competitive interactions between these two are complex and are mediated by both the acidity of the water and the density of competitors.

Adverse Environmental Impacts

Habitat Loss: The Barking Treefrog has undoubtedly suffered major declines since European colonization due to the widespread loss of both seasonal wetlands and terrestrial habitats. In modern times urbanization (e.g., Delis et al. 1996, Pieterson et al. 2006), road construction, wetland drainage and filling, and deforestation associated with agricultural and intense silviculture (tree farms) have destroyed or degraded habitats throughout the range. Limited data suggests that this species can do well in managed forests that are on long rotation cycles so long as breeding sites are retained nearby (Hanlin et al. 2000).

Status in North Carolina

NHP State Rank: S4

Global Rank: G5

Environmental Threats: Urbanization and the continued loss of seasonal wetlands and forested habitats for the adults is the greatest concern for existing populations in North Carolina.

Status Comments: Populations in North Carolina appear to be stable in most areas. We have several historical records for counties in the central Coastal Plain near the northern limit of the range in North Carolina, but almost none in recent times (see iNaturalist). This suggests that populations may be in decline in this region. Populations in coastal forests, in the Sandhills, and along the Fall Line and adjoining areas of the eastern Piedmont appear to be stable.

Stewardship: Local populations are best maintained by having a cluster of seasonal or semipermanent ponds that periodically dry to exclude fishes, along with a forest buffer of perhaps 100-200 m that surrounds the breeding sites.

Photo Gallery for Hyla gratiosa - Barking Treefrog		7 photos are shown.
	Recorded by: H. Talcott, P. Halpin Moore Co.	Recorded by: H. Talcott, P. Halpin Moore Co.
	Recorded by: David George Chatham Co.	Recorded by: Tom Howard Wake Co.
	Recorded by: Tom Howard Wake Co.	Recorded by: Mark Shields Carteret Co.
	Recorded by: J. Shimel New Hanover Co.

Hyla gratiosa - Barking Treefrog

Photo Gallery for Hyla gratiosa - Barking Treefrog

7 photos are shown.