Amphibians of North Carolina

Scientific Name:	Common Name:		Family (Alpha):

Hylidae Members:
Hyla chrysoscelis - Cope's Gray Treefrog

caption

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. Cope's Gray Treefrog (Hyla chrysoscelis) and the Gray Treefrog (H. versicolor) are two morphologically indistinguishable species that are members of a polyploid complex. Hyla chrysoscelis is a diploid species (2N = 24 chromosomes), while H. versicolor is a tetraploid (4N = 48 chromosomes). The exact origin of H. versicolor has intrigued evolutionary biologists and generated several hypotheses that are supported to varying degrees by molecular and genetic analyses. Holloway et al. (2006) proposed that H. versicolor arose via several speciation events from H. chrysoscelis-like diploid ancestors and two other now extinct lineages of tree frogs. A recent analysis that used a much more comprehensive set of molecular data suggests that H. versicolor most likely formed via a single genome duplication event that involved only H. chrysoscelis and did not involve hybridization with other species (Booker et al. 2021). Since then, there has been significant hybridization between diploids and tetraploids where they co-occur. This has led to the reformation of distinct polyploid lineages following the initial whole genome duplication event. Despite evidence of a complex evolutionary history that involves the repeated re-formation of H. versicolor lineages through time, researchers treat the diploid and tetraploid forms of this complex as only two species. Since they are morphologically identical, the two species can only be differentiated using other evidence such as the chromosome number or voice characteristics. Fortunately, these species are rarely found in sympatry in North Carolina and can usually be identified based on locality. Hyla chrysoscelis occurs statewide, but H. versicolor is only known from a northern tier of counties in the Piedmont near the Virginia border, and from one record from Rowan County in the Piedmont.
Species Comments: As noted by Dodd (2013), many of the older publications concerning gray treefrogs are compromised because of the inability to determine if the species that was studied was H. versicolor or H. chrysoscelis. This is a particular problem in areas of sympatry where both species could potentially occur at a study site.

Identification

Description: H. versicolor and H. chrysoscelis are morphologically indistinguishable and the following description of H. chrysoscelis applies equally to both species. Cope's Gray Treefrog is a small to medium-sized frog with conspicuous toe pads, granular skin, and a lichen-like dorsal pattern. The dorsal patterning of the adults often consists of a grayish ground color that is overlain by darker patches. However, the ground color can vary from ashy white to pale brown or greenish, and individuals can change body color to better match their backgrounds (Beane et al. 2010, Dodd 2013). The juveniles generally tend to be greener than the adults and often have rather poorly developed dark patches. There is a conspicuous whitish patch underneath the eye that is often lined on the sides with a thin black line. The upper surface of the legs have dark bands and the rear toes are partially webbed. The concealed surfaces of the back legs are mottled with bright orange and blackish pigmentation near the margins, and washed with bright orange elsewhere. The belly, throat, and undersides of the front legs are whitish and unmarked, except for males which have dark vocal sacs during the breeding season. The males typically average about 8-12% smaller than females based on SUL (Dodd 2013). The respective average sizes of males and females from Virginia were 42 and 48 mm SUL (Mitchell 1986), while specimens from Tennessee were 46 mm SUL (range = 39–53) and 52 mm SUL (range = 45–62 mm; Ritke et al. 1990). Most adults in Georgia vary from 28-44 mm SUL, with a maximum length of 52 mm. Beane et al. (2010) reported a range of 32-62 mm for adult specimens in the Carolinas and Virginia. The hatchlings vary from 4-7 mm TL and are brownish with black mottling on the tail. There is a pair of preorbital stripes, but they are not distinctly outlined and only become apparent after two weeks (Dodd 2013). As the tadpole grows, the venter becomes more cream colored with a heavy intrusion of gold flecks on the posterior end. The mature tadpole can reach 64–65 mm TL, but are typically much smaller (Dodd 2013, Jensen et al. 2008). This species has inducible defenses against predators. Tadpoles in ponds with predatory dragonfly larvae respond by developing relatively large, brightly colored tail fins with dark spots along the margins (McCollum and Van Buskirk 1996). So, expect significant variation depending on local site conditions. H. versicolor and H. chrysoscelis can only be distinguished in the field by the trill rates of calling males (pulses per second). Recordings of calling males are recommended for later analysis at sites where both species could be present. Mitchell and Pague (2011) conducted an extensive survey of populations in Virginia and found that there is no overlap in the trill rates of the two species when recorded in the field (prior to adjusting for temperature differences). The mean and standard deviation for trill rates for H. chrysoscelis was 45.8 (4.89) versus 24.54 (3.42) for H. versicolor. In essence, any field recording that shows a trill rate of < 30 pulses/sec can be assigned to H. versicolor with very high confidence.
Vocalizations: The advertisement call is a loud fast trill. The trill of this species is higher pitched and occurs at a faster pulse rate (34–69 notes per second) than that of H. versicolor (17–35 notes/sec). The pulse rate varies depending on the ambient temperature and location, but averages between 44 and 59 pulses/sec at 24°C (Dodd 2013). Each trill last less than a second, and sequential trills are spaced 2-6 seconds apart. In addition to the advertisement call, other vocalizations are made that include a “rain call” that is often heard from high in the trees when a storm is approaching or conditions suddenly become cloudy. These frequently occur outside of the breeding season and their function is unknown. Males also have a release call that is issued if a male is amplexed or comes into contact with another male. It consists of a series of high-pitched "erps" or "yips". An aggressive call that sounds like the alarm call of a hen turkey is often issued if two individuals come into close contact.
Technical Reference: Dodd (2013)
Online Photos: Google iNaturalist
Observation Methods: Individuals are most easily observed around the breeding sites on nights following afternoon thunderstorms or other rain events. They are also commonly seen on roads on rainy nights, and around homes where they frequently feed around outdoor lights at night.

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AmphibiaWeb Account

Distribution in North Carolina

Distribution Comments: Hyla chrysoscelis is found in the eastern US where it ranges from southern New Jersey southward to southern Florida and westward to central Texas. The range extends northward through eastern Oklahoma and eastern Kansas as a broad arm to northern Minnesota and Wisconsin. Farther east it extends from the Gulf States to as far north as West Virginia, southern Ohio, southern Indiana and southern Illinois. Disjuncts are known from several sites in the Great Lakes region and South Dakota. This species is found statewide in North Carolina and is common in all three physiological provinces. Populations in the Blue Ridge are mostly found in the lower valleys, but are occasionally encountered at higher elevations where local breeding sites are present.
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: This highly arboreal species is most commonly associated with deciduous hardwood forests where it blends in well with tree limbs in the forest canopy. Populations in the upper Midwest at the western edge of the Eastern Deciduous Forest are sometimes found in prairies and oak savanna habitats, and southern populations can be found in cypress stands. Populations use a variety of forest habitats so long as suitable breeding sites are nearby. Examples include oak-hickory forests, northern hardwood forests, mixed pine-hardwood forests, bottomland and slope forests, hardwood swamps, cypress savannas, cypress/gum ponds, and inland hydric hammocks (Dodd 2013).

The adults generally prefer fish-free seasonal or semi-permanent wetlands for breeding, but will use permanent ponds with fish --particularly where vegetated shallows are present that provide a degree of spatial segregation from fish. Commonly used habitats include vernal ponds in forests, marshes, flooded fields and floodplain overflow pools, beaver ponds, roadside ditches, puddles and flooded tire ruts, small farm ponds, and the shallow sections of lakes. Individuals have readily taken to using water features in urban and suburban settings and are commonly seen around homesites and in ornamental gardens. Felix et al. (2010) experimentally manipulated forest canopy cover and found that the adults prefer sunny or partially shaded sites over closed canopy forests. Similar studies using experimental pools in Virginia yielded similar results (Binckley and Resetarits 2007).

In North Carolina, this highly arboreal species is associated with hardwood forests over most of the state. The adults are often heard calling from high up in the canopy. In some areas -- particularly the Coastal Plain -- mixed stands of hardwoods and conifers (pines, cypresses, and white cedars) may be used, but the coloration of the adults seems to serve primarily as camouflage against the lichen-covered, rough gray bark of hardwoods. A wide range of pools and ponds are used for breeding within the state, including vernal ponds, freshwater marshes, flooded fields, puddles and other rain-filled depressions, beaver ponds, and farm ponds. Rivers and streams do not appear to be used, but oxbows, sloughs and other still-water habitats in floodplains may be used. Many of the breeding sites are isolated enough to lack fish, but at least some of the larger impoundments used by this species support fish populations. This species also frequently uses garden and ornamental ponds in residential areas.

Environmental and Physiological Tolerances: Breeding sites include both acidic waters in the Coastal Plain and waters with higher pH in the Piedmont and Blue Ridge. This species ranges as far south as southern Florida and is presumably more heat-tolerant than the Gray Treefrog. Schurbon and Fauth (2003) found that populations may be eliminated or depressed at sites with frequent prescribed burns, probably due to the strong suppression of hardwood trees around breeding sites.

Biotic Relationships: The adults generally prefer fish-free habitats for breeding, and both the eggs and larvae are palatable to fish and a variety of other aquatic predators such as insect larvae, Ambystoma larvae and newts. Grubb (1972) found that the Western Mosquitofish (Gambusia affinis) will eat the eggs in captivity, and Ambystoma larvae will also (Ritke and Mumme 1993). The larvae appear to lack chemical defenses against fish (Kats et al. 1988, Semlitsch and Gibbons 1988), and Ambystoma larvae will decimate larval populations when confined together in experimental enclosures (Cortwright and Nelson 1990).

The tadpoles are frequently killed and eaten by aquatic invertebrates such as dytiscid beetles and odonate larvae and have evolved inducible defenses that reduce attack success. When confined with dragonfly larvae, the developing tadpoles develop relatively large, brightly colored tail fins with orangish or reddish coloration and blackish spots or mottling along the margins. These entice predators to strike the tail region rather than the more vulnerable head and body (McCollum and Van Buskirk 1996). More details studies by Richardson (2006) showed that tadpoles will develop these defenses when exposed to either alarms cues from an injured tadpole, or metabolites that are released when an odonate digests its prey. In addition, H. chrysoscelis tadpoles will develop defenses when dragonflies are fed tadpoles of a closely related species (Pseudacris crucifer) that shares breeding ponds. When exposed to chemical cues from invertebrate predators, they will also reduce movements, which presumably lowers their encounter rates with predators (Haislip et al. 2012).

Breeding adults can reduce the adverse impacts of predators and competitors on their offspring by selecting oviposition sites that are favorable. Resetarits and Wilbur (1989) set up an array of experimental pools with different species and found that females laid fewer eggs in pools that held Spotted Salamander larvae, Blackbanded Sunfish (Enneacanthus chaetodon) or conspecific tadpoles that were potential competitors. Females did not avoid pools with the Eastern Newt, American Bullfrog tadpoles, or larval dragonflies (Tramea carolina). A similar study in Mississippi (Resetarits et al. 2018) further demonstrated avoidance of fish, and showed that females also prefer relatively large ponds for ovipositing. In another study, Pintar and Resetarits (2017) found that females selected habitats with both lower predation risk from Ambystoma larvae -- particularly A. talpoideum -- and lower desiccation risk (deeper versus shallower experimental ponds).

Petranka et al. (2007) examined the colonization and use of an array of constructed ponds in western North Carolina and found that pond use was curtailed after fish colonized certain ponds. It is uncertain if this was due to adults shifting to nearby fish-free sites, or fish eliminating the tadpoles, but the former seems more likely. Sexton and Phillips (1986) made similar observations following fish invasions in two Missouri ponds. Collectively, these studies indicate that adult choice of oviposition sites is an important adaptation to minimize predation on offspring.

The juveniles and adults are presumably taken by a variety of predators such as aquatic snakes, birds, and raccoons, but there are few documented records. The lichen-like patterning of the adults provides remarkable camouflage when resting on the bark of hardwood trees, and young juveniles that are often green blend in well with foliage. The bright orangish coloration on the back legs is revealed when a frog jumps and the sudden display of bright coloration may startle a would-be predator long enough for the frog to escape (Dodd 2013). The adults have noxious skin secretions that can irritate the eyes and mucous membranes of human handlers.

See also Habitat Account for General Hardwood Forests

Life History and Autecology

Breeding and Courtship: The adults have a prolonged breeding season that lasts from mid-spring through the summer months in most areas. The males typically begin calling following the spring warm-up and leaf-out in April and continue through August. Calling may begin as early as February in Florida (Carr 1940a) and March in other southern locales such as Louisiana, Alabama, Georgia, and Tennessee (Dodd 2013). Calling in North Carolina generally begins in April. Egg laying rarely begins before mid-March in southern populations and can continue through August or September.

Although reproduction can occur over several months, Godwin and Roble (1983) found that individual males in a Kansas population usually called for only a few nights during the breeding season (mean = 4.2 nights). Calling is energetically expensive and individuals appeared to take feeding breaks in the canopy before returning to the pond to call again. Males that called for a relatively large number of nights (> 4) generally had a better chance of mating at least once during the breeding season. Other studies also indicate that individual males often spend only one or two nights calling during the breeding season (Morris 1989, Ritke and Semlitsch 1991).

The males often call from high in the trees during the day, then descend to nearby breeding sites with the onset of darkness and begin calling around the ponds. Chorusing and breeding occurs during rainy nights or when rains have occurred earlier in the day. The males usually call while perched on branches or small limbs 0.5-2.5 m above the waterline (Dodd 2013, Ritke et al. 1990), but will also call from the pond proper on floating algae mats, dense grasses, clumps of vegetation, and bare soil (Godwin and Roble 1983). Males that gather around the breeding sites either establish territories or act as satellite males. The dominant males will aggressively defend their calling sites by kicking, shoving, head-butting, or jumping on an intruder (Dodd 2013). Only a small percentage of individuals in a population are satellite males (Roble 1985b). These subordinates normally remain silent, but may quickly take over a perch site and begin calling once an amplexed pair departs for the breeding site (Dodd 2013, Fellers 1975, Ritke and Semlitsch 1991).

The females begin appearing at the breeding sites about an hour after the males begin chorusing at dusk. The females actively choose their mates, and appear to select a male based on both his call characteristics and perch site (Bee 2008a, Bee and Schwartz 2009, Dodd 2013, Littlejohn 1958). At least at some sites, females tend to select larger males as mates (Morris 1989). After a female moves to a calling male, she initiates amplexus by prodding the male or crawling on his back. Once amplexed, the pair may remain near the perch site for several hours before moving to the pond to oviposit and fertilize the eggs. They often do not descend to the breeding site until after midnight.

Reproductive Mode: When ready to oviposit, the female arches her back and thrusts her legs rearward, which positions her cloaca above the water surface and close to the male. Egg packets are released and fertilized, after which the female’s cloaca is submerged and the eggs float away on the water's surface (Dodd 2013). The female may swim a short distance away, then deposit another packet of eggs. This is repeated until the entire compliment is laid. The eggs are deposited in small floating monolayers that contain from <20 to as many as 100 eggs. The freshly laid ova are around 1.2–1.4 mm in diameter and are surrounded by an egg capsule that is 3.5-6.6 mm in diameter (Dodd 2013). Development is rapid and the embryos hatch with a few days after the eggs are laid.

The mean clutch size varies among populations and increases with female body length (Dodd 2013). Reported clutch sizes include 1,500 in North Carolina (Resetarits and Wilbur 1991), 2,060 (range = 628-4,208) in Tennessee (Ritke et al. 1990), 2,600 in Virginia (Mitchell 1986), and 3,401 (range 1,086 to 4,797) in Arkansas (Trauth et al. 1990).

Aquatic Life History: The tadpoles are active mid-water feeders. They also consume algae and detritus that is rasped from plant material and the substrate, along with the associated bacteria, fungi, and small metazoans that live on this material (Dodd 2013). Akers et al. (2008) found that larvae grow faster in turbid water with nutrient-rich colloidal clay suspensions relative to when in clear water.

Very little data are available on growth rates, survival, and length of the larval period in natural ponds, primarily because of staggered breeding and the difficulty of recognizing different age cohorts. The hatchlings grow rapidly and typically transform after 1-2 months of growth (Dodd 2013), but growth rates, survival, and length of the larval period vary depending on factors such as ambient temperatures, the quality and quantity of food, pond hydroperiods, the extent of both intra- and interspecific competition, and the types and densities of predators that can play an important role in mediating competition. Some of the reported sizes of froglets at metamorphosis that were summarized by Dodd (2013) are 12.3–15.0 mm SUL in Florida (Hellman 1953), 15–16 mm in Arkansas (Trauth et al. 1990), 15.8 mm SUL (range 12 to 19 mm SUL) in Tennessee (Ritke et al. 1990), 13–20 mm SUL in the Great Smokies (Dodd 2004), and as small as 13 mm in southeastern Georgia (Wright 1932). The full-grown larvae often exceed 30-40 mm TL or more. The tadpoles are preyed upon by numerous aquatic predators such as odonates and other insects, mole salamander larvae, newts, and fishes.

Terrestrial Life History: We have much to learn about the terrestrial ecology of this species. Very little is known about the ecology of the juveniles. Limited evidence suggests that they may stay close to the breeding sites after metamorphosing and may overwinter there during their first winter (Fitch 1958). However, studies of the closely related H. versicolor show that the young disperse away from the breeding ponds shortly after metamorphosing (Roble 1979). Rasche et al. (2020) surmised that the young metamorphs might use the sound of calling adults to orient while moving away from the natal ponds or towards adjoining ponds, but found no evidence to support this.

During the warmer months of the year the adults live in the forest canopy where they rest on bark or conceal themselves in crevices, tree holes, woodpecker holes, and other types of cavities (Dodd 2013). Like some other frogs, they use their legs to wipe themselves with a waterproofing material composed of mucous and lipids (Barbeau and Lillywhite 2005). During the winter, they appear to move out of the tree canopy into more insulated sites such as under logs, in loose soil beneath leaf litter, and inside hollow trees (Johnson 2005, Trauth et al. 2006). They can overwinter safely in loose soil beneath leaf litter by using glucose as a cryoprotectant that protects against freezing (Costanzo et al. 1992, Burkholder 1998).

Godwin and Roble (1983) found that the adults stay in arboreal feeding sites close to the breeding sites, and move down to call and mate following rain events. Pittman et al. (2008) used a grid of PVC pipes to study seasonal use at a pond in the Piedmont of North Carolina. The frogs mostly used wooded areas in the immediate vicinity of the pond and showed strong site fidelity based on recaptures in the pipes. Individuals were active on the surface except during the colder months (November-February).

Ritke et al. (1991) found that 29% of marked adults in Tennessee returned the following year to breed, while Roble (1985) estimated that only 5% of males and 2.5% of females did so at a study site in Kansas.

General Ecology

Population Ecology: Most local populations appear to consist of no more than a few hundred adults, and often times far fewer. Ritke et al. (1991) marked adult frogs that breed a cluster of ponds in western Tennessee and found that individuals exhibited strong site fidelity. Most returned to their home ponds to breed in subsequent years, but a few moved between ponds that were separated by as much as 0.48-0.63 km. This suggests that this species has elements of metapopulation structure. Population regulation could potentially occur in both the larval stage due to density-dependent competition for food resources, or possibly during the adult stage in association with the territorial behavior of calling males.

Community Ecology: Hyla chrysoscelis has been used in several studies of experimental pond communities and laboratory trials where various combinations of competitors and predators have been added to examine community interactions. The larvae are quickly eaten by fish, but large tadpoles can sometimes minimize predation from small, gape-limited fish. The tadpoles may also reduce predation risk by hiding in cover, reducing their activity levels, and developing morphological defenses such as broad tail fins with bold markings when exposed to predatory odonates (e.g., McCollum and Van Buskirk 1996, McCollum and Leimberger 1997, Semlitsch and Gibbons 1988).

Crowding with both conspecifics and heterospecifics generally tends to reduce larval growth rates and survivorship, lengthen the larval period, and decrease the average size at metamorphosis (Alford 1989a, Wilbur 1987). These responses, in turn, can potentially act as density-dependent mechanisms to limit the sizes of local populations. The Eastern Newt is an effective predator of this and other anuran larvae in cattle tanks and can release the surviving tadpoles from competition by reducing the densities on both conspecifics and heterospecifics (Morin 1983). The relative time of arrival at a breeding site can also affect competitive outcomes between species. In general, arriving late is costly for H. chrysoscelis and other community members (Wilbur and Alford 1985). In North Carolina, individuals will readily colonize newly constructed ponds that have relatively few predators and competitors (Petranka et al. 2007).

Researcher have largely relied on experimental communities to examine interactions between community members due to the ease of controlling experimental conditions. We still have much to learn about the extent to which competition, predation, and priority effects structure natural communities.

Adverse Environmental Impacts

Status in North Carolina

NHP State Rank: S5

Global Rank: G5

Environmental Threats: Populations show no evidence of catastrophic declines throughout the range despite extensive historical losses of both the aquatic and terrestrial habitats from urbanization, agriculture, the filling of wetlands, deforestation, and the replacement of hardwood forests with pine monocultures (Dodd 2013). Roadkill is always an issue for amphibians that migrate to and from breeding sites, and pesticides and other toxic substances are harmful to both the tadpoles and adults (e.g., Anderson and Arruda 2006, Westerman et al. 2003). Populations in fragmented landscapes can often be maintained by having deciduous forest buffers along riparian corridors. Although thousands of farm ponds have been created in North Carolina, most are not suitable habitats either because they have fish or are too far from surrounding forests that provide critical habitat for the adults.

Status Comments: Populations of (H. chrysoscelis) show no evidence of marked declines in North Carolina and appear to tolerate habitat fragmentation and urbanization reasonably well so long as tracts of deciduous forests and breeding sites are retained on the landscape.

Stewardship: Local populations are best maintained by having deciduous hardwoods next to fish-free breeding sites. A cluster of breeding ponds that are within a few hundred meters of each other provide elements of metapopulation structure and allow adults the opportunity to shift to alternate breeding sites as needed.

Recording Gallery for Hyla chrysoscelis - Cope's Gray Treefrog
	2022-05-23. Beaufort Co. Jim Petranka and Becky Elkin -

Photo Gallery for Hyla chrysoscelis - Cope's Gray Treefrog		37 photos are available. Only the most recent 30 are shown.
	Recorded by: B. Bockhahn Sampson Co.	Recorded by: Steve Hall, Carol Tingley, Tom Howard, David George, Pat Coin, Jeff Niznik, Chatham Co.
	Recorded by: Stephen Hall Durham Co.	Recorded by: K. Bischof Transylvania Co.
	Recorded by: Andrew W. Jones Yadkin Co.	Recorded by: Andrew W. Jones Yadkin Co.
	Recorded by: David George Chatham Co.	Recorded by: Caleb Garner Wake Co.
	Recorded by: Caleb Garner Wake Co.	Recorded by: David George Orange Co.
	Recorded by: David George Chatham Co.	Recorded by: David George Chatham Co.
	Recorded by: Travis McLain Cabarrus Co.	Recorded by: K. Williams Surry Co.
	Recorded by: Chuck Smith Davidson Co.	Recorded by: Chuck Smith Davidson Co.
	Recorded by: John Petranka Orange Co.	Recorded by: Jim Petranka and Becky Elkin Beaufort Co. Comment: Spectrogram of a single male calling from a roadside ditch.
	Recorded by: Steve Hall Durham Co.	Recorded by: Steve Hall and Dee Stuckey Orange Co.
	Recorded by: Dee Stuckey and Steve Hall Orange Co.	Recorded by: Mark Basinger Wilson Co.
	Recorded by: Mark Basinger Wilson Co.	Recorded by: Rob Van Epps Mecklenburg Co.
	Recorded by: Hunter Phillips Onslow Co.	Recorded by: Salman Abdulali Pitt Co.
	Recorded by: Salman Abdulali Pitt Co.	Recorded by: N. Bowman Surry Co.
	Recorded by: Mark Shields Onslow Co.	Recorded by: Jim Petranka Madison Co.