Amphibians of North Carolina

Scientific Name:	Common Name:		Family (Alpha):

NC Records
Sole representative of Microhylidae in NC
Gastrophryne carolinensis - Eastern Narrow-mouthed Toad

Taxonomy

Class: Amphibia

Order: Anura

Family: Microhylidae

Subfamily: Microhylinae


Taxonomic Comments: Eastern Narrow-mouthed Toad (Gastrophryne carolinensis) and Western Narrow-mouthed Toad (G. olivacea) were once treated as subspecies of a single species but are now treated as separate species based on molecular data and evidence of significant reproductive isolation.
Species Comments:

Identification

Description: Adults of the Eastern Narrow-mouthed Toad are small frogs with short hind legs, a rotund body, a pointed snout, and a distinctive fold of skin across the back of the head. The head is flattened and small, and the rear feet have small spades that are used for digging (Dodd 2013, Jensen et al. 2008). The skin on the back and sides has a slightly granular texture, but is smooth relative to our true toads. The dorsal ground color is variable and encompasses a range of earth colors including gray, clay-colored, brownish red, or even black. Individuals may be rather plain, or have varying levels of fine dark or light mottling. Many individuals show evidence of a broad and irregular tan, reddish or chestnut band on each side that extends from the eye towards the groin. The belly is usually heavily speckled or mottled with varying levels of light to dark gray on a lighter background. The adults vary from 19–39 mm SUL. Males have a dark throat patch and usually average 3-10% smaller in SUL than females (Dodd 2013, Meshaka and Layne 2015). Coastal Plain populations also tend to average smaller than inland populations (Nelson 1972). The mature tadpoles are brownish to black with either a light stripe, or two or three light, elongated blotches on either side of the posterior portion of the body. A light stripe extends along the middle of the tail musculature from the base towards the tip. It is often more pronounced on the anterior half of the tail or may terminate near the middle of the tail. The jaws lack both keratinized teeth and an oral disk (Dodd 2013). The tail fin is of medium width and may have varying degrees of darker mottling. The tadpoles are rather small and are typically 15-30 mm TL (maximum = 38 mm).
Vocalizations: The males emit a buzzy or bleating "waaaa" call that is one of the most nasally songs of any of our native frogs. The characteristics of the call vary with temperature, but each "waaaa" typically last around 0.5-2.5 seconds, with pauses between calls that are commonly 5-10 seconds or more. When chorusing, two or more males often call in tandem, with the first call immediately triggering one or more nearby males to call. Calling bouts occur intermittently and are usually interrupted by periods of silence (Dodd 2013). On a spectrogram, the nasal quality is characteristic of calls that consist of a stack of "partials." These are bands at different frequencies where one group is the dominant pitch band where most of the energy is concentrated. The dominant band is usually located well above the fundamental, or lowest pitched band (Pieplow 2017). In the spectrogram shown below, the dominant frequency is indicated by the brightest band, which is located in the middle of the stack. Fowler's Toad has a similar "waaaa" call but has a lower dominant pitch -- typically around 2 kHz instead of 3 kHz or higher as is typical of Gastrophryne. It also has a distinctive upward slur at the beginning of each call that is absent in Gastrophryne, although a brief peep note may precede the "waaaa" call in Gastrophryne (Conant and Collins 1991, Elliot et al. 2009).
Technical Reference: Dodd (2013)
Online Photos: Google iNaturalist
Observation Methods: The adults tend to be secretive and are most easily observed when at the breeding sites at night. They can occasionally be found on roads during rainy weather and are sometimes uncovered beneath boards, logs, and other cover objects.

Download Video: "MP4"
AmphibiaWeb Account

Distribution in North Carolina

Distribution Comments: The Eastern Narrow-mouthed Toad occupies a broad region of the southeastern US from an area roughly extending from east to west from the Delmarva Peninsula through south-central Kentucky, southern Illinois, southern Missouri, and extreme southeastern Kansas. The range extends southward along the Atlantic Seaboard to southern Florida, and farther west through eastern Oklahoma, eastern Texas, and all of the Gulf States and Georgia. The species is generally absent from the mountainous regions of western Virginia, West Virginia, eastern Kentucky, and the southern Appalachians. In North Carolina, populations occur throughout the Coastal Plain and in much of the eastern and central Piedmont. This species is rare in the western Piedmont and was only recently documented in the Blue Ridge in Madison County.
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: The juveniles and adults are generalists that can be found in a wide variety of habitats that range from wet or mesic environs to relatively dry upland forests. Individuals can quickly desiccate if exposed to very dry substrates and require moist microhabitats for resting and foraging. They generally favor habitats with dense leaf litter and surface debris that covers organic soils. However, they can survive in dry sites by either using animal burrows, crevices, and root channels that have high humidity, or by burrowing in sandy or loamy soils (Dodd 2013).

Some of the known forested habitats include cypress-gum swamps, bottomland hardwoods, mixed pine-hardwood forests, deciduous hardwood forests, upland pine forests, and pine-oak woodlands. They also utilize a variety of disturbed and urban habitats where there are suitable breeding sites and cover for the adults. Examples include fields and meadows, golf courses, and urban lawns and gardens (Dodd 2013). This species also appears to be mildly salt-tolerant and has been found near coastal marshes and in close proximity to beaches. Krysko et al. (2019) noted that this species can be found in virtually every terrestrial habitat that occurs in Florida.

The breeding sites are most commonly seasonal or semipermanent habitats that are fish-free, but large ponds with fish are sometimes used. Breeding sites may range from small puddles in roads to large cypress ponds. Some of the natural habitats listed by Dodd (2013) include woodland pools, marshes, sloughs, seasonally flooded forests, depression wetlands, sinkhole ponds, cypress savannas, cypress/gum ponds, and beaver ponds. A variety of other artificial habitats are used such as roadside ditches, borrow pits, farm ponds, flooded agricultural fields and large semipermanent lakes with vegetated shallows.

In North Carolina, the juveniles and adults also occupy a wide range of habitats, including barrier island grasslands, bottomland and swamp forests, Longleaf Pine savannas and flatwoods, mesic hardwoods, dry woodlands, and a variety of disturbed sites. Breeding likewise takes place in a diversity of habitats including bottomland swamps, marshes, vernal ponds, cypress/gum swamps, roadside ditches, borrow pits, rain pools in pastures, farm ponds, sloughs, and flooded agricultural fields. Fish-free waters are preferred but some use is made of beaver ponds and other pools where fish are present.

Environmental and Physiological Tolerances: Brown and Walls (2013) found that G. carolinensis is more sensitive to salinity that other species that were tested, with larvae unable to survive salinities that exceeded 5 parts per thousand.

Biotic Relationships: The tadpoles lack chemical defenses against aquatic predators. Baber and Babbitt (2003) found that three native fishes in Florida (Fundulus chrysotus, Gambusia holbrooki, Jordanella floridae) and the introduced Walking Catfish (Clarias batrachus) will readily consume the tadpoles, with the native species being more effective predators. These species often colonize seasonal ponds when flooding connects them to more permanent waters such as nearby streams (e.g., Hohausova et al. 2010). In instances like this, the larvae are severely impacted following fish invasions. Baber and Babbitt (2004) found that predation rates for Gambusia holbrooki were reduced when varying amounts of cover were manipulated in experimental pools. Survival was higher than that of H. squirella, which is a more active swimmer.

Fauth and Resetarits (1991) demonstrated that the Eastern Newt and the Lesser Siren are very effective predators on the larvae when confined together in experimental pools. The larvae are also taken by odonates and other aquatic invertebrates. Schiwitz et al. (2020) found that the larvae reduce movements when exposed to either caged odonate larvae or to caged larvae that were fed tadpoles. In the wild, this would presumably reduce their encounters rates with these sit-and-wait predators.

The juveniles and adults produce noxious and toxic skin secretions that greatly reduce predation rates from many vertebrate predators. The skin secretions are produced by granular glands located throughout the skin and first appear when individuals are metamorphosing. Garton and Mushinsky (1979) offered adults to a watersnake (Nerodia erythrogaster), a gartersnake (Thamnophis sirtalis), a turtle (Chelydra serpentina), and a wading bird (Black-crowned Night Heron) and found that all were far more likely to reject these relative to other frogs that served as controls. Most released the prey immediately after biting it and exhibited distress behavior.

Despite having chemical defenses, there are a few documented cases of predation by snakes (Thamnophis sp.; Agkistrodon contortrix) and unidentified mammals (Dodd 2013). Fogarty and Hetrick (1973) found 48 adults in the guts of Cattle Egrets in Florida. Gastrophryne carolinensis tends to be an ant specialist, and the sticky secretions on the back may help to protect against ant attacks. The fold of skin behind the eyes can also be moved forward to cover and protect the eyes from ants (Nelson 1972).

See also Habitat Account for General Mixed Habitats

Life History and Autecology

Breeding and Courtship: Calling and breeding in most areas of the range begins in spring with the arrival of warm weather and may continue though September or October. This is a warm-weather species and males generally will not call until the air temperatures exceed 19.5°C (Dodd 2013). The breeding season varies regionally and with latitude. Some examples of regional variation in Florida include year-round breeding in the Florida Keys, breeding from June-September at the Archbold Biological Station in south-central Florida, and breeding from May-through October at the nearby Buck Island Ranch (Meshaka and Layne 2015). Calling occurs from June to September in eastern Tennessee (Dodd 2004), from April to August in Arkansas (Trauth et al. 2004), and during July and August in Virginia (Mitchell 1986). Beane et al. (2010) reported April-October breeding for the Carolinas and Virginia, as did Jensen et al. (2008) for Georgia.

Heavy rains such as those associated with passing fronts or afternoon thunderstorms often trigger strong chorusing. Dodd (2013) noted a general seasonal tendency for calling to occur mostly at night early in the breeding season, then become progressively more likely to occur both during the day and night as the season progresses. Recent rains also appear to be less important in triggering chorusing as the breeding season progresses.

The adults live in terrestrial habitats that may be substantial distances from the nearest breeding site. Dodd (1996), for example, captured individuals in north-central Florida that were from 42–914 m (mean = 420 m) from the nearest breeding site. Movements to and from the breeding sites typically occur after dark and are usually triggered by rainfall (e.g., Dodd 1995, Meshaka and Woolfenden 1999). Dodd and Cade (1998) found that directional movements into and out of a breeding site in Florida changed annually. There was no evidence that the adults used movement corridors between nearby terrestrial refugia and aquatic breeding sites.

Once they arrive at the breeding sites, the males and females make short daily treks to and from the breeding sites from nearby terrestrial retreats. The males arrive shortly before the females and immediately set up calling positions in shallow water, and typically where they are partially concealed by vegetation, fallen branches, or other cover (Dodd 2013). When calling, the males raise the front of their bodies while often propping on a support structure so that the vocal sac projects well above the waterline. Sex ratios appear to be only slightly male-biased at breeding ponds, and the males show no evidence of being aggressive or territorial. They often call in close proximity to one another (Anderson 1954, Dodd 2013, Trauth et al. 1999).

A female will usually approach a calling male by swimming with her body floating and her rear legs widely extended. The male then approaches the female from behind and slowly works his way up the female’s back. A male often has a difficult time amplexing a female because of his short limbs and her rotund body. In addition to using his arms to clasp, the male produces a sticky dermal secretion that functions to attach himself to the female (Conaway and Metter 1967, Dodd 2013). Oviposition normally occurs 1.5–2 hrs after the initiation of amplexus.

Reproductive Mode: An amplexed pair may swim around for two or more hours before oviposition begins. Shortly before oviposition, the female moves the rear part of her body toward the water’s surface so that the cloaca is above the water surface. The male then slides forward to position his cloaca into close proximity with that of the female’s. The eggs are fertilized as they stream from the female in groups of 10–150 eggs that form a rounded or squarish monolayer on the water surface (Anderson 1954, Dodd 2013). Repeated bouts of fertilization occur until the female finishes laying, at which point the male may remain clasped for a short time before detaching from the female. It is uncertain to what extent females deposit their full clutch of eggs or only part of their clutch when mating.

The freshly laid eggs are dark brown or blackish above and usually whitish or yellowish white below. They vary from 0.7–1.3 mm in diameter and are surrounded by a jelly envelope that is 2.8 to 4.0 mm in diameter (Dodd 2013, Livezey and Wright 1947, Wright 1932, Trauth et al. 1999). The surface film of eggs consists of separate eggs that will float apart if disturbed. The surface monolayers can vary considerable in size depending on the number of eggs in each raft (Wright 1932), but raft diameters of 5-15 cm are common. The embryos develop quickly and hatching occurs within a few days after oviposition (Wright 1932).

Dodd (2013) noted that the range in reported clutch sizes varies considerably and may in part be due to females laying only partial clutches, although this has yet to be clearly demonstrated. Anderson (1954) counted from 152–1,089 ovarian eggs in Missouri females (mean = 510), with the mean number increasing from 378 eggs for 2-year olds to 681 eggs for 4 -yr olds. Trauth et al. (1999) found from 186–1,459 ovarian eggs per female (mean = 673) for Arkansas specimens, but there was no relationship between female length and clutch size. Mitchell and Pague (2015) reported a mean of 821 eggs (range = 208-1,614) for females that oviposited in captivity, while Meshaka et al. (2015) reported clutches of 278-1618 eggs (mean = 825) for 14 museum specimens from Virginia. Clutch size was not significantly related to female snout-vent length in either of these studies.

Aquatic Life History: The eggs are often laid in warm, shallow sites and the larvae grow quickly. The tadpoles lack cornified, rasping mouthparts and are strict filter-feeders on zooplankton and phytoplankton. They are less mobile and active than many seasonal pond breeders, and are generally less vulnerable to sight-oriented predators than fast swimmers. The eggs are frequently laid in ephemeral sites and the larvae often succumb to pond drying. Although seasonal sites can be risky in this regard, their ephemeral nature periodically eliminates fishes and other predators that can greatly reduce the output of juveniles (Semlitsch et al. 1996). The length of the larval period in natural sites is poorly documented. Wright (1932) estimated the larval period to be 23–67 days in southeastern Georgia. The young metamorphs typically average around 10-11 mm SUL, with a range of 7–13 mm SUL (Anderson 1954, Dodd 1995, Wright 1932).

Terrestrial Life History: The juveniles presumably leave the breeding sites within several weeks after metamorphosing and make their way to terrestrial feeding sites. They are very likely vulnerable to desiccation and other risks when moving into unknown territory. Dodd and Cade (1998) found that the metamorphs in Florida commonly used temporary wetlands as stopping points as they dispersed from their natal sites.

The juveniles and adults are secretive and live a mostly semifossorial or fossorial existence. They can quickly desiccate if subjected to dry conditions and seek out moist microhabitats as daytime retreats. They are commonly found in forested habitats with thick leaf litter and organic soils. They also take shelter beneath logs, piles of bark, debris piles, and a variety of other natural and artificial cover, including boards, flower pots, sheets of tin, and debris in trash piles. They sometimes use the burrows of other animals such as crayfishes and mammals, and are capable to digging their own burrows with their hind limbs (Dodd 2013).

Individuals will often sit in their burrows or beneath surface cover with only the top portion of the head visible at the surface. From there they ambush ants and other passing prey. They most commonly become surface active during and following rains or when conditions are otherwise moist (Dodd 1995), and are most active from dusk though the first few hours after dark. Tinkle (1959) marked individuals that were under scattered boards and found that most were rather sedentary, with the maximum distance moved between captures being around 3 meters. Individuals may be active year-round in Florida, but are only active during the warmer months of the year in the northern part of the range where the winters are cold (Dodd 1995, 2013).

Gastrophryne carolinensis is an ant specialist, although it takes other small invertebrates such as mites, spiders, isopods, snails, collembolans, beetles, true bugs, flies, and termites (Brown 1974, Dodd 2013). Deyrup et al. (2013) conducted a detailed study of ant predation in Florida. They recovered 4,859 ants from 146 stomachs. Forty-three species of ants were consumed and they comprised about 95% of all food items, mostly species of Pheidole or Nylanderia. Most were small species (4 mm or less in length) that are nocturnally active. The authors noted that many of the species produce venoms, chemical repellents, or other organic substances in exocrine glands and raised the possibility that these chemicals may be stored in the skin or tissues of the frogs. The juveniles and adults very likely set-up burrows and retreats close to ant mounds where they can efficiently forage on abundant food resources.

Studies that were conducted in Arkansas and Missouri indicate that many juveniles reach sexual maturity and breed the first spring after metamorphosing, although some females may not lay their first set of eggs for another year (Anderson 1954, Trauth et al. 1999). It is uncertain if an additional year of growth is required for females in southern locales such as southern Florida. The adults probably rarely live for more than 4-5 years in the wild (Dodd 1995).

General Ecology

Population Ecology: Local populations are centered around the breeding sites, which may contain one or more local ponds. Successful reproduction in this species tends to be episodic, with premature pond drying often resulting in 100% mortality prior to metamorphosis, and females sometimes skipping breeding in dry years (Daszak et al. 2005, Dodd 1995, Semlitsch et al. 1996, Wright 1932). Local breeding population sizes fluctuate accordingly. It is not uncommon for multi-year studies to document several thousand adults across years (e.g., Dodd 1992, Greenberg and Tanner 2005a), which suggests that local populations that use clusters of ponds may commonly number in the thousands. Dodd (2013) noted that this species can be ubiquitous within landscapes that have numerous wetlands, and that the adults can be very common in terrestrial forests as well (e.g., Bennett et al. 1980, Dodd et al. 2007).

Makowsky et al. (2009) conducted a phylogeographic analysis of populations across the range of G. carolinensis using both mtDNA and nuclear (AFLP) markers and did not find any significant phylogeographic structure. This was surprising given that individuals show evidence of fidelity to breeding sites or clusters of local breeding sites, and have low vagility compared to most other terrestrial vertebrates. They surmised that G. carolinensis may have experienced a population bottleneck in the past that was followed by a rapidly expanded of its geographic range.

Community Ecology: The Eastern Narrow-mouthed Toad often shares breeding ponds with a variety of predators and potential competitors, particularly when using sites with relatively long hydroperiods. Fauth and Resetarits (1991) examined interactions between two predators (Eastern Newt; Lesser Siren) and five species of anuran larvae in experimental tanks. Newts were very effective predators on Gastrophryne and other anurans. In their absence, Gastrophryne performed well when competing with other species that shared the tanks.

Adverse Environmental Impacts

Habitat Loss: Gastrophryne carolinensis is fairly tolerant of human disturbance, but populations have undoubtedly been lost due to urbanization and large-scale agricultural operations. They appear to tolerate silviculture reasonably well so long as breeding sites and suitable moist microhabitats and retreats are present for the adults (Dodd 2013). Populations also tolerate prescribed burns well and are frequently found in fire-maintained habitats.

Status in North Carolina

NHP State Rank: S5

Global Rank: G5

Environmental Threats: Loss of habitat from urbanization and agricultural operations are the most important threats for North Carolina populations. Losses (road kill) from vehicular traffic is an ever increasing problem for this and other amphibians that cross roads while migrating to and from breeding sites.

Status Comments: Gastrophryne carolinensis is widespread and relatively abundant in North Carolina and there is no evidence of ongoing widespread population declines.

Stewardship: Local populations are best maintained by having a cluster of seasonal breeding sites that are within or near forested habitats.

Recording Gallery for Gastrophryne carolinensis - Eastern Narrow-mouthed Toad
	2022-05-25. Beaufort Co. Jim Petranka and Becky Elkin - calling from a vegetated ditch with dozens of Hyla squirella.

Photo Gallery for Gastrophryne carolinensis - Eastern Narrow-mouthed Toad		37 photos are available. Only the most recent 30 are shown.
	Recorded by: Mark Shields Onslow Co.	Recorded by: Mark Shields Onslow Co.
	Recorded by: Mark Shields Onslow Co.	Recorded by: Andrew W. Jones, Atley Elliott Polk Co.
	Recorded by: Andrew W. Jones, Atley Elliott Polk Co.	Recorded by: Andrew W. Jones Polk Co.
	Recorded by: Andrew W. Jones Polk Co. Comment: Eggs that were deposited in shallow water.	Recorded by: R. Newman Carteret Co.
	Recorded by: A. Ledford Wake Co.	Recorded by: Steve Hall and Savannah Hall Orange Co.
	Recorded by: Morgan Freese New Hanover Co.	Recorded by: Hunter Phillips Onslow Co.
	Recorded by: Morgan Freese Dare Co.	Recorded by: Morgan Freese Dare Co.
	Recorded by: j.wyche Gates Co.	Recorded by: j.wyche Gates Co.
	Recorded by: j.wyche Gates Co.	Recorded by: Morgan Freese Durham Co.
	Recorded by: G. Schneider, J. Murvine Stanly Co.	Recorded by: G. Schneider, J. Murvine Stanly Co.
	Recorded by: F. Williams, S. Williams Gates Co.	Recorded by: j.wyche Gates Co.
	Recorded by: j.wyche Gates Co.	Recorded by: J. Wyche5 Gates Co.
	Recorded by: J. Wyche5 Gates Co.	Recorded by: W. Stanley Cumberland Co.
	Recorded by: W. Stanley Cumberland Co.	Recorded by: J. Wyche Gates Co.
	Recorded by: Jane Wyche Gates Co.	Recorded by: Jane Wyche Gates Co.