Amphibians of North Carolina
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NC Records

Hyla cinerea - Green 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.

Hyla cinerea occasionally hybridizes with H. gratiosa and calling sites appear to be important in preventing breeding mistakes. The former normally calls from bushes or emergent vegetation above the water, while H. gratiosa calls from the water surface. At a site in Alabama where bushes have been removed from the edges of ponds, male H. cinerea have been forced to call from the ground and frequently intercept and mate with female H. gratiosa that are moving towards calling males in the pond (Lamb 1987, Mecham 1960a, Schlefer et al. 1986). Hybrids between these species have been documented elsewhere in the range.

Barrow et al. (2018) analyzed mtDNA variation in populations in the Southeast and found evidence of two populations in the westernmost sample area that were highly divergent from a central clade and an eastern clade. In contrast, analyses of nuclear genes resulted in poorly resolved gene trees.
Species Comments: The Green Treefrog has been used extensively as a model for integrated studies in auditory, behavioral, and neural physiology (Redmer and Brandon 2003).


Identification
Description: Hyla cinerea is a large, slender, bright green treefrog with smooth skin, conspicuous toe pads, and long, lanky legs. Most adults are bright green above, but specimens are sometimes silvery green, yellowish, grayish, olive, brown or gray depending on temperature and other factors such as the color of the background upon which they are resting (Dodd 2013). Most individuals have a prominent dorsolateral white stripe on each side that extends from the upper lip to the groin area. The stripe often has a thin dark margin and is sometimes infused with yellow. On some individuals it is missing altogether, while on others it may terminate well before reaching the groin area (Duellman and Schwartz 1958). Less prominent white stripes are often present along the lateral edges of the front and hind limbs, particularly on the lower regions of the limbs. The head and upper body surface sometimes have small, scattered, yellow spots that often have black borders. The belly is white or cream colored, and the hind toes are fully webbed (Dodd 2013). Males have a white to yellowish subgular vocal pouch and are nearly as large as the females. The adults vary from 28-66 mm SUL, with most falling in the 40-60 mm range. The average length for different populations typically varies from around 44-53 mm SUL.

The hatchlings are 4.5-5.5 mm TL and the small tadpoles are light yellowish brown. They become various shades of green with age and develop a yellow preorbital stripe that extends from the eye to the tip of the snout (Dodd 2013, Redmer and Brandon 2003). Small tadpoles develop a gold mid-body crossband of yellow iridophores that disappears with age. The dorsal tail fin originates well forward on the body, is arched, and about the same width as the ventral fin. The tail musculature and fins of older larvae are dull yellow and overlain with dark mottling or reticulations that can vary from faint to very bold. The belly is light yellow or buff, and the eyes are laterally displaced.
Vocalizations: Breeding males have an advertisement call that resembles a nasal "queenk" "queenk" "queenk" or "quonk" "quonk" "quonk" that is repeated around 60-80 times per minute in the field. If a subordinate male enters the calling territory of a dominant male, the calling male may issue a more pulsed call that is an encounter or agonistic call. Fellers (1979a) found that these are produced if an approaching male comes within about 170 cm of the territory holder. Adjoining males frequently alternate their calls so there is no overlap, and may adjust their call characteristics depending on neighboring calls (Garcia et al. 2019). Females can discriminate between calling males and use voice characteristics when selecting mates (e.g., Laird et al. 2016).

In the field, chorusing usually begins with one or a few males initiating a calling bout, then more joining in until a lake or pond reverberates in a deafening chorus. Calling then abruptly ceases within a few minutes and a new bout begins after several minutes of silence. Dodd (2013) noted that on large lakes where thousands of individuals are sometimes present the bouts resemble waves of noise as the cycle repeats itself among resident populations.
Technical Reference: Dodd (2013)
Online Photos:    Google   iNaturalist
Observation Methods: Green Treefrogs are most commonly heard and observed along the vegetation-choked margins of ponds, marshes, and lakes. They can also be found crossing roads on rainy nights and are commonly seen around homes at night where they are often attracted to insects that gather around lights.

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AmphibiaWeb Account
Distribution in North Carolina
Distribution Comments: The Green Treefrog is found primarily in the southeastern Coastal Plain from the Delmarva Peninsula southward to southern Florida, then westward through the Gulf States to eastern Texas. The range extends northward to western Tennessee, Arkansas, and southeastern Oklahoma before ending in western Kentucky, southern Illinois, southern Indiana, and southeastern Missouri. In many areas it can also be found in adjoining areas outside of the Coastal Plain. This in part reflects a substantial range expansion that has occurred during the last 50-60 years as populations have colonized natural breeding sites, as well as constructed ponds, lakes and reservoirs (e.g., Jensen et al. 2008, Lodato et al. 2014, Redmer et al. 1999). The range expansion has undoubtedly been facilitated by the release of pets, or the accidental transport of animals in or on boats, vehicles or nursery stock.

Populations in North Carolina occur throughout the Coastal Plain and have expanded their range well into the eastern and central Piedmont. They currently occur as far west as the Charlotte-Gastonia and Winston-Salem areas. As of 2022 there are four records from the western mountains in urban settings that undoubtedly reflect introduced animals. This species is now also well established in eastern Tennessee with records from Gatlinburg, Pigeon Forge, and Johnson City and surrounding areas.
Distribution Reference: Beane et al. (2010), Dodd (2013), Redmer and Brandon (2003)
County Map: Clicking on a county returns the records for the species in that county.
GBIF Global Distribution
Key Habitat Requirements
Habitat: The adults are commonly found in or around permanent or semipermanent bodies of water and spend much of the year along the margins of the breeding sites. Outside of the breeding season they frequent nearby forested areas and can be found in a variety of habitats such as upland and bottomland hardwood forests, mixed pine-hardwood forests, hardwood hammocks, and ecotones between forested and open areas. They also tolerate brackish water to some extent and have been found in mangrove forests and forested habitats that fringe coastal marshes (Dodd 2013). Individuals are commonly encountered around buildings and homes that they use as hiding and foraging sites.

The preferred breeding habitats are bodies of water with vegetation-choked margins. Emergent plants such as cattails, iris beds, broadleaf plants, shrubs, or other rank vegetation provide good resting and calling sites, and areas with duckweed or dense mats of floating or shallowly submerged vegetation offer protection for the larvae. All sorts of freshwater habitats are used. Examples include sluggish streams with vegetated shorelines, canals, swamps, sloughs, marshes, lakes, reservoirs, beaver ponds, farm ponds, sewage ponds, fish-farm ponds, flooded borrow pits, flooded sink-holes, and flooded ditches. Habitats that may be saline are also used such as coastal marshes, salt marshes, and other areas with brackish water (Dodd 2013).

In North Carolina, populations can be found in and around beaver ponds, farm ponds, lakes and reservoirs, bottomland swamps, waterfowl impoundments, Carolina Bays, flooded canals, the sluggish portions of streams, and other permanent or semipermanent bodies of water. Sites with cattails or other lush, rank shoreline vegetation are preferred. The green color of the frogs provides an excellent match to the bright green colors of the plants on which they rest during the day.

Although this is primarily a species of the Atlantic and Gulf Coastal Plains, they may once have been strongly associated with beaver ponds farther inland. The range in North Carolina is continuing to expand into the Piedmont where ponds, lakes, and urban water features are used as breeding sites. The westward spread of beavers following their reintroduction in North Carolina in the late 1940s may have also facilitated the spread westward. Others have probably been introduced by pet owners and by hitch-hiking in or on vehicles and boats. This species is also very common on barrier islands, where local populations occur in both freshwater and brackish marshes.

Environmental and Physiological Tolerances: Hyla cinerea appears to be fairly tolerant of acidic waters and has been found in Carolina bays with a pH as low as 4.3 (Dodd 2013). It also appears to be somewhat tolerant of saline conditions and has been observed in water that is saline to 8.3 parts per thousand (Brown and Walls 2013, Diener 1965, Dodd 2013). Albecker and McCoy (2017) surveyed populations on the Outer Banks in North Carolina and found local populations at sites with even greater salinities, with one at 16.8 ppt and a second at 23.4 ppt.

When grown experimentally with salt concentrations between 2-8 parts per thousand (ppt), increasing salinity tends to slow growth and reduce size at metamorphosis (Schriever 2007). Brown and Walls (2013) found that exposure of tadpoles to 12 ppt or higher results in 100% mortality within 72 hours. The embryos are more sensitive, with mean LC50 values for early stage embryos around 5.2 ppt (Schriever 2007). Albecker and McCoy (2017) obtained similar results for both inland and coastal populations in North Carolina, although coastal populations tolerated salt stress better than inland populations.

Wilder and Welch (2014) found that females lay fewer eggs in experimental pools that were slightly brackish (4 ppt) relative to controls with freshwater. Albecker and McCoy (2017) found a similar pattern of avoidance for inland adults, but not for adults from coastal areas.

Biotic Relationships: Green Treefrog tadpoles are mostly found in permanent bodies of water, but occasionally occur in seasonal ponds. As such, they are exposed to a wide variety of predators, with odonates dominating the seasonal ponds and fishes the permanent ponds. Gunzburger and Travis (2004, 2005a) conducted studies with an array of potential predators that occur in Florida and found that larvae were vulnerable to predation from all of the test species. Bass, newts, and odonate larvae were the most effective predators, but giant water bugs, dytiscid larvae, crayfish, mosquitofish, the Flier Sunfish, and musk and mud turtles also fed on the larvae. Small larvae (8 mm TL) were most vulnerable, while the largest larvae (27 mm TL) suffered almost no losses. Garton and Brandon (1975) noted that fishes (Umbra, Fundulus, Aphredoderus) and water bugs (Belostoma) also readily ate the tadpoles from a southern Illinois site.

Gunzburger and Travis (2005a) found that intraguild predation commonly occurs when multiple predators are used in experiments. Nonetheless, H. cinerea tadpoles had very low survival regardless of the combination of predators that were used in the experiments. Although fishes and odonates are major predators, the tadpoles have either chemical or behavioral defenses that make them less vulnerable than other species such as H. gratiosa (Blouin 1990, Gunzburger 2005). The tadpoles tend to decrease activity when exposed to potential predators such as odonate larvae, fishes, and newts (Richardson 2001). Local populations are also typically found at sites with extensive regions of floating or subsurface aquatic plants which likely provide cover and refugia for the young tadpoles (Garton and Brandon 1975).

The juveniles and adults are taken by a wide variety of vertebrates. Some of the known predators include the Killdeer, the Western Ratsnake (Pantherophis obsoletus), the North American Racer (Coluber constrictor), the Eastern Ribbon Snake (Thamnophis saurita), the Common Watersnake (Nerodia sipedon), the Snapping Turtle (Chelydra serpentina), as well as wading birds, raccoons, foxes, and spiders (Dodd 2013, Redmer and Brandon, AmphibiaWeb). They appear to rely heavily on camouflage and immobility to avoid detection, and also perch well above the waterline during the day to reduce predation risk from aquatic predators. Garton and Brandon (1975) noted that calling males tend to move away from the edges of ponds at night to possibly avoid raccoon predation. They also frequently call above the waterline at night to avoid fish and snake predation. When approached by snakes, individuals may inflate their bodies or use their limbs to try to prevent ingestion (Dodd 2013).
See also Habitat Account for General Shoreline Forblands
Life History and Autecology
Breeding and Courtship: Males normally do not begin calling in earnest until April or later, but limited calling may begin as early as February or March in southern populations. Calling typically continues until August-October depending on the locality (Dodd 2013). Calling in Illinois begins in May and extends to August (Garton and Brandon 1975, Redmer et al. 1999), while in the Carolinas and Virginia it occurs from April through September (Beane et al. 2010). Gaul and Mitchell (2007) heard calling in North Carolina from May through August. Breeding and egg laying begins shortly after the males begin their seasonal chorusing. It can begin as early as March in Alabama and Florida, but most breeding occurs between April and August in most areas of the range (Dodd 2013). Gravid females in Virginia were only present from the end of April through early July, with a May–June peak (Meshaka et al. 2020).

The males most commonly call from an elevated position that is usually < 1 m above the water line (Garton and Brandon 1975, Mitchell and Miller 1991). Calling sites can be on small trees like willows, on wetland shrubs like buttonbush and swamp rose, or on cattails, water hyacinths, pickerelweed, water lotus, irises, and many other types of rank vegetation. Garton and Brandon (1975) observed that males sometimes called from at or near the water surface on floating logs and mats of floating vegetation, particularly during the peak breeding season. Individuals will sometimes call during the day during rainy or overcast weather, but chorusing typically begins with the onset of darkness. Calling is very energetically expensive (Prestwich et al. 1989) and usually only lasts for 3-4 hours after dark (Mohr and Dorcas 1999). Although recent rainfall tends to stimulate calling, it is not essential, and choruses can be heard almost every night during the peak of the breeding season (Garton and Brandon 1975).

The calling males stake out small territories and produce both an advertising call to attract females and an encounter call to warn intruders of their trespass. Nearest neighbors often engage in vocal dueling bouts where they alternate their advertisement calls to avoid overlap with their neighbor. Fellers (1979a) observed that encounter calls are issued whenever an intruder gets closer than 1.7 m of the territory holder. One or more non-calling satellite males are often present in the immediate vicinity of calling males that are occasionally successful in intercepting females that are approaching a calling male (Perrill et al. 1978). If satellite males cannot be driven away using encounter calls, then aggressive struggles may ensue that involve wrestling, head-butting, or chasing the intruder away (Dodd 2013). Satellite males general remain as non-calling subordinates, but will quickly assume the role of the dominant male if it leaves with an amplexed female or is removed experimentally (Perrill et al. 1982).

Females are often surrounded by several calling males in close proximity and use call characteristics to pick a mate (Gerhardt 1978, Gerhardt and Klump 1988, Neelon and Höbel 2017). Each female approaches a calling male of her choosing and initiates axillary amplexus by touching the male or crawling over his back. This triggers the male to amplex her. The pair typically remains amplexed for 4-5 hours as ovulation proceeds before making their way to the water to lay and fertilize the eggs. When laying the female depresses her back and extends her limbs downward, which positions her cloaca near the male's cloaca for fertilization (Garton and Brandon 1975).
Reproductive Mode: Each female typically lays 10-15 or more small groups of 10–50 eggs each. They tend to sink, but are usually attached to aquatic vegetation at or near the water's surface where the water is well oxygenated. The freshly laid eggs are black or brown above and white to cream underneath and vary from 0.8–1.6 mm in diameter. They are surrounded by an inner envelope that is 2–3.4 mm in diameter and a rather poorly defined outer envelope that is 3.2–5.0 mm in diameter (Dodd 2013, Livezey and Wright 1947). The embryos hatch within 2-4 days and vary from 4.5-5.5 mm TL (Garton and Brandon 1975).

Perrill and Daniel (1983) marked amplexed females in Georgia and found that around 15% returned either once or twice to lay additional clutches, with a mean of 19 days between clutch deposition dates. This percentage is probably an underestimate since many marked females that returned to breed may not have been observed. Clutches for a single breeding bout ranged from 275 to 1,160 eggs (mean = 790). Other estimates of clutch sizes vary, in part due to the fact that some are based on the number of eggs deposited, while other are based on ovarian egg counts. Estimates based on the number of eggs deposited are 359 to 2,658 eggs (mean = 1,214) in Florida (Gunzburger 2006), 478–1,061 (mean = 700) in Illinois (Garton and Brandon 1975), 275–1,160 (mean = 814) in Georgia (Perrill and Daniel 1983) and 689–2,228 (mean = 1,272) in Virginia (Mitchell and Prague 2014). Estimates based on ovarian egg counts include 550-4,034 (mean = 1990 ova) in Florida (Delis 2001), 1,348–3,946 (mean = 2,152) in Arkansas (Trauth et al. 1990), and 442–1473 (mean = 884 ova) in Virginia (Meshaka et al. 2020). Most studies have found that clutch size increases with female SUL.
Aquatic Life History: The eggs are normally laid in shallow areas with dense submergent or floating vegetation that the larvae use as foraging sites and as a partial refuge from fishes and other predators. The larval period lasts from about 5-9 weeks, and is influenced by environmental factors such as water temperatures, food quality and quantity, and the density and types of competitors and predators (Gunzburger 2007). Blouin (1992) manipulated food level and temperature and found that larvae grew faster and were smaller at metamorphosis when raised at a relatively high temperature (30C versus 25C). Higher food rations had the usual effect of increasing growth rates and size at metamorphosis, and shortening the larval period.

Garton and Brandon (1975) estimated a larval period of 4-6 weeks, with the larvae transforming when 20-23 mm SUL. The first metamorphs were found in late June and July about 28-44 days after the first large choruses were heard. Wright (1932) estimated the larval period to last 55-63 days in Georgia, with metamorphs varying from 11.5-17 mm SUL. The largest tadpoles observed by Wright (1932) were 40 mm TL, versus 60 mm TL by Garton and Brandon (1975). Hatchlings that were grown by Gunzburger (2007) in enclosures that were place in natural ponds metamorphosed after 25-50 days on average depending on site conditions.
Terrestrial Life History: Garton and Brandon (1975) and Redmer et al. (1999) found numerous young metamorphs on emergent vegetation at study sites in Illinois where they rested and remained immobile during the day like the adults. They actively moved about after dark and fed, and remained through September after the adults had already moved onto land in early August. The juveniles dispersed away from the breeding site in September and October where they were found as far 60 m from the water. They grew rapidly and by early September were 25-41 mm SUL. By the following June many appeared to be sexually mature based on the smallest calling males being 47 mm SUL. Subadults that were not mature often remained in close proximity to calling males until they became sexually mature.

The juveniles and adults mostly feed around dusk and at night, but are sometimes active during the day on rainy or overcast days (Dodd 2013). Individuals appear to be gape-limited generalists that take a wide range of palatable prey. Several dietary studies have been conducted that show that a broad diversity of insects and other taxa are eaten (Brown 1974, Dodd 2013, Freed 1982, Haber 1926, Kilby 1945, Thigpen et al. 2016). Common insectivorous prey include coleopterans, dipterans, lepidopterans, orthopterans, odonates, hymenopterans and hemipterans. Many other taxa of insects are taken, as well as snails, spiders, mites, collembolans, millipedes, and phalangids. Freed (1980) conducted laboratory trials and found that the frogs were more likely to consume active prey (flies) versus stationary prey (mosquitoes). In another study, Freed (1982) found representatives of 35 families of invertebrates specimens from Florida. Samples of invertebrates in the field -- along with feeding trials (Freed 1980)-- suggest that the size and the rate of movement of prey are two important features that can affect the likelihood of a prey item being eaten.

Individuals in southern populations may be active nearly year-round, while those in the northern part of the range overwinter in refugia. Dodd (2013) noted that during cold or dry weather individuals find shelter beneath coarse woody debris or boards, under bark, in sawdust piles, treehole crevices and in other protective refugia. In northern Florida, there appears to be a peak in movement to winter retreats in November (Zacharow et al. 2003), and the juveniles and adults may spend the autumn through late winter months substantial distances away from the breeding sites. Dodd (1996) found individuals from 457 to 914 m (mean = 545 m) from the nearest breeding site in northern Florida. In extreme south Florida, seasonal movements between habitats are more closely tied to the wet and dry seasons (Waddle 2006).
General Ecology
Population Ecology: Very little is known about the population biology of this species. Local populations can vary from a dozen or so to thousands of adults. Carr (1940), for example, noted that choruses may continue unbroken for 10 to 12 km of river front. Large lakes with vegetated shallows can also support thousands of individuals (Dodd 2013). We have little data on the genetic structure of clusters of local and regional populations.
Community Ecology: Green Treefrogs breed during the spring and summer months in waters that typically have fishes and other aquatic predators. Fish will readily consume the larvae, and their primary defenses appear to be behavioral. The larvae spend most of their time in vegetated shallows that are less frequently used by fishes. They also will reduce their activity levels in the presence of predatory fish. Invertebrate predators such as odonate larvae can reach high densities in semipermanent habitats, but not as much so in permanent habitats where fishes prey upon them. It is possible that the larvae are mostly found in permanent habitats due to high mortality rates from odonates in fish-free habitats (Gunzburger and Travis 2004, 2005). The larvae could potentially compete with many other community members for food, but this has been poorly researched.
Adverse Environmental Impacts
Status in North Carolina
NHP State Rank: S5
Global Rank: G5
Environmental Threats: Local populations are exposed to the usual threats associated with human population growth, including the loss of natural wetlands, urbanization, deforestation, and the use of pesticides and other toxic compounds. Countless thousands are killed on roads every year as they move to and from wetlands (e.g., Smith and Dodd 2003). Despite human impacts, this species has adapted reasonably well to anthropogenic disturbances.
Status Comments: Hyla cinerea is a widespread and abundant species, and the range is expanding in several areas (Dodd 2013). This species seem to tolerate disturbed and habitat fragmentation reasonably well and appears to be increasing in numbers in North Carolina where the range has expanded into many areas of the Piedmont.
Stewardship: Local populations do best where there are permanent habitats with well-vegetated shallows and nearby hardwood or pine-hardwood forests.

Recording Gallery for Hyla cinerea - Green Treefrog

2021-05-05. Orange Co. Steve Hall - Large chorus heard at dusk; singing from a large, forb-covered slough

2022-05-23. Beaufort Co. Jim Petranka and Becky Elkin - A pair with alternating calls.

Photo Gallery for Hyla cinerea - Green Treefrog

44 photos are available. Only the most recent 30 are shown.

Recorded by: B. Bockhahn
Sampson Co.		Recorded by: Louis Skrabec
Guilford Co.
Recorded by: R. Newman
Carteret Co.		Recorded by: Guy McGrane
Watauga Co.
Recorded by: Paul Hart, Tom Worden
Harnett Co.		Recorded by: Steve Hall, Pat Coin, David George, and Mark Basinger
Chatham Co.
Recorded by: David George, Jeff Niznik
Chatham Co.		Recorded by: Judith West
Randolph Co.
Recorded by: David George
Orange Co.		Recorded by: David George
Orange Co.
Recorded by: David George
Orange Co.		Recorded by: Jack V.
Beaufort Co.
Recorded by: R. Newman
Carteret Co.		Recorded by: Chuck Smith
Davidson Co.
Recorded by: Mark Basinger
Brunswick Co.		Recorded by: David George
Durham Co.
Recorded by: Travis McLain
Anson Co.		Recorded by: Travis McLain
Cabarrus Co.
Recorded by: Travis McLain
Cabarrus Co.		Recorded by: Mark Basinger
Wilson Co.
Recorded by: Rob Van Epps
Mecklenburg Co.		Recorded by: R. Newman
Carteret Co.
Recorded by: Mark Shields
Duplin Co.		Recorded by: Carrie DeJaco
Stanly Co.
Recorded by: Steve Hall and Jim Petranka
Richmond Co.		Recorded by: Steve Hall
Durham Co.
Recorded by: Mark Shields
Dare Co.		Recorded by: Jim Petranka and Becky Elkin
Beaufort Co.
Comment: Spectrogram of a pair with alternating calls.
Recorded by: Steve Hall
Durham Co.		Recorded by: R. Newman
Carteret Co.