Amphibians of North Carolina

Scientific Name:	Common Name:		Family (Alpha):

NC Records
Bufonidae Members:
Anaxyrus fowleri - Fowler's Toad

Taxonomy

Class: Amphibia

Order: Anura

Family: Bufonidae

Synonym: Bufo fowleri


Taxonomic Comments: Fowler's Toad (Anaxyrus fowleri) and Woodhouse's Toad (A. woodhousii) were previously considered to be subspecies of a single species, but Masta et al. (2002) provided evidence based on mtDNA analyses that they should be treated as separate species. Although these forms extensively hybridize in Texas, Louisiana, eastern Oklahoma, and southwestern Arkansas they are generally treated as separate species by most authorities. Fowler's Toad hybridizes with several other species of toads, including the Southern Toad and the American Toad. This typically happens when a male amplexes a female of an opposing species where the two share a breeding site (Dodd 2013). In North Carolina hybridization appears to happen on occasion with both the American Toad and Southern Toad (Beane et al. 2010, Gaul and Mitchell 2007, Wilbur et al. 1978), but needs to be verified using genetic markers.
Species Comments:

Identification

Description: Fowler's Toad is a medium-sized toad, with most adults ranging from 45-82 mm SUL (maximum length 92-95 mm). The males commonly average around 10-20% less than the females in a local population based on SUL, but in some populations sexual differences are minimal (Dodd 2013). Males commonly average around 54-57 mm in local populations versus 60-72 mm for females. The dorsal ground color is often grayish to light brown, but can be various other colors such as reddish, reddish brown, or dark brown. The dorsal patterning is also variable, but most individuals have a series of roundish or oblong dark blotches that frequently have narrow, cream-colored borders. These occur on the top of the eyes, on either side of the mid-dorsal stripe, in the dorsolateral region, and on the upper portions of the legs. The largest blotches typically have three to five small warts each, which is characteristic of this species. Individuals usually have a narrow mid-dorsal stripe that extends from between the eyes to the end of the body. The stripe is usually whitish or cream-colored and is of uniform width along its length. The belly is white and often either immaculate or with a dark spot in the middle of the chest, although individuals are sometimes more heavily spotted. The cranial crests are less conspicuous than those of A. americanus and A. terrestris and lack prominent posterior knobs. The transverse, postorbital crest directly touches the paratoid gland and is not separated by a gap or connecting spur. Like other toads, the hind feet have enlarged, cornified tubercles for digging. Sexually active males have darkened throat pouches and cornified patches on the thumbs that are used to grasp females. Fowler's Toad closely resembles both the American Toad and the Southern Toad. This species lacks enlarged warts on the hind legs, and typically has three or more warts in each of the largest dorsal blotches on the back (versus one or two in A. americanus). The transverse, postorbital crest touches the front of the parotoid gland directly, rather than being separated by a gap or connecting spur. The mid-dorsal stripe is also relatively uniform in width versus irregular in width as seen in the American Toad. The Southern Toad is best separated from Fowler's Toad by the presence of large knobs on its prominent cranial crests, and in having only one or two warts per blotch. Fowler's Toad sometimes hybridizes with both the American Toad and the Southern Toad and specimens are occasionally found that are difficult to assign to species (Beane et al. 2010, Dodd 2013). The tadpoles are small and uniformly dark brown to blackish. They have ovoid bodies and dorsally placed eyes, and frequently form large aggregations in shallow water. The tadpoles of A. fowleri may be impossible to distinguish in the field from those of A. americanus and A. terrestris.
Vocalizations: Males produce a loud explosive advertisement call that sounds like “waaaah” and lasts for about two or three seconds. These are produced in long series, with each interrupted by a pause that typically last 3-10 seconds. Anaxyrus fowleri also has a release call that is a vibrating chirp that serves to alert both conspecific and heterospecific males that the amplexed animal is not a female.
Technical Reference: Dodd (2013)
Online Photos: Google iNaturalist
Observation Methods: Fowler's Toad can be found on rainy or warm nights on roadways and is sometimes attracted to building and street lights where individuals feed on insects. Adults can be observed at the breeding ponds during the spring, and the distinctive calls offer an easy way to obtain new locality records.

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AmphibiaWeb Account

Distribution in North Carolina

Distribution Comments: Fowler's Toad is found throughout a broad region of the eastern US and extreme southern Canada. In the US, populations occur from New Hampshire and eastern Vermont southward along portions of the Atlantic Seaboard to the Florida Panhandle. The range extends westward to Louisiana and eastern Texas in the south, and to eastern Oklahoma, extreme eastern Kansas, western Missouri, southeastern Iowa and much of Illinois. Several disjuncts are known from western Iowa, eastern Kansas, northwestern Missouri, and the eastern shore of Lake Erie. This species extensively hybridizes with A. woodhousii in Texas, Louisiana, eastern Oklahoma, and southwestern Arkansas and most specimens cannot be confidently assigned to species in these regions (Dodd 2013). Fowler's Toad is common in the Piedmont of North Carolina, but uncommon and spottily distributed at lower elevation sites in the mountains. We have records from much of the Coastal Plain counties except for the southeastern corner where this species appears to be absent or rare (Beane et al. 2010). Populations have been documented at several sites on the Outer Banks.
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 generally prefer open habitats with friable soils that allow them to dig to avoid physiologically stressful conditions. Sites with sandy or sandy-loam soils and nearby breeding sites provide optimal habitats. Examples of the terrestrial habitats that are used throughout the range of this species include well-drained woodlands, dry scrub, lake shores and terraces, oak savannas, sand and beach dunes, coastlines, and river banks and terraces (Dodd 2013). Populations are commonly found in riparian habitats and have adapted to using human-altered landscapes with fields, pastures, and other open habitats. Jones and Tupper (2015) conducted a landscape analysis of sites in Virginia and Maryland and found that populations are less likely to be present where there are deciduous forests, hay crops, development and agricultural pesticide use.

The breeding sites vary from small seasonal wetlands to large reservoirs and are most common in sunny or partially shaded locations. The larvae have chemical defenses against fishes and other aquatic predators, and commonly occur in habitats with fishes. Frequently used habitats include water-filled ruts and puddles in roads, flooded fields, seasonal pools and marshes, beaver ponds, farm and golf course ponds, retention ponds, and lakes and reservoirs. This species breeds later in the year than the American Toad and shows a general preference for semipermanent or permanent habitats. The adults will also use shallow, quiet sections of streams where there is little or no current, including quiet areas in blackwater habitats in the Coastal Plain. When using large, permanent habitats such as reservoirs the females often select shallow water for egg-laying (Dodd 2013).

In North Carolina, populations likely bred in beaver ponds, marshes, seasonal ponds, and floodplain and scour pools along rivers prior to European colonization. They now commonly use constructed sites such as farm ponds, golf course ponds, and reservoirs. Populations are found on several of North Carolina's barrier islands where the vegetation is typically sparse and the soils sandy. Breeding there takes place in freshwater depression ponds rather than the saline marshes along the sounds. This species is often found in early successional habitats, but is uncommon in mature deciduous forests where it tends to be replaced by the American Toad.

Environmental and Physiological Tolerances: Fowler's Toad is less cold-tolerant than the American Toad, reaching only as far north as New England, the Lower Peninsula of Michigan, and as a disjunct in southern Ontario. In the North Carolina this species is absent from the higher elevations in the mountains (Beane et al. 2010). Conversely, it appears to be heat-tolerant, ranging as far south as the Gulf Coast and occurring throughout most of the North Carolina Coastal Plain. Populations in the Coastal Plain of North Carolina often use blackwater habitats, which may indicate a greater degree of acid tolerance than the American Toad.

Biotic Relationships: Like our other native toads, both the larvae and adults produce toxic or noxious skin secretions that help to ward off predators. The chemical defenses of the larvae to aquatic predators are not as well studied as those of closely related forms such as A. americanus. The larvae are largely unpalatable to the Largemouth Bass (Micropterus salmoides) and other centrarchid fishes (Kruse and Stone 1984, Lawler 1989), but are regularly eaten by the Eastern Newt. Larvae often respond to newts and fish by reducing their movements (Lawler 1989). Aquatic insect predators with piercing-sucking mouthparts are largely immune to the toxins.

The juveniles and adults have poison glands on the skin that are concentrated on the warts and parotoid glands. These help to repel attacks from both aquatic and terrestrial predators. When approached, individuals will often remain motionless, but may also flee if provoked. If attacked they often will inflate the body, lower the head and raise their hindquarters, or tilt the body in the direction of the attacker. This helps to direct the warts and parotoid glands towards the predator (Dodd 2013). Some snakes like hog-nosed snakes (Heterodon spp.) are immune to the poisons. Some predators also learn to attack toads through their ventral surfaces, which lack poison glands. As much as 75% of the diet of Heterodon may be comprised of this and other species of toads. Other predators include snapping turtles (Chelydra), aquatic and semiaquatic snakes (Nerodia; Thamnophis), the North American Racer (Coluber constrictor), several species of birds, and raccoons and skunks (Dodd 2013).

See also Habitat Account for General River Bars and Sparsely Vegetated Shorelines

Life History and Autecology

Breeding and Courtship: Males move to the breeding sites from the surrounding uplands during the spring warm-up and begin chorusing with the arrival of warm days and nights. Males typically will not call if ambient temperatures are below 10–14°C (Breden 1988, Green 1989) and most females tend to enter the ponds and mate when chorusing is at its seasonal peak (Dodd 2013). Males that chorus after the peak are often unsuccessful in finding mates. Breeding typically begins in March in southern populations in Alabama, Mississippi and Louisiana (Brown 1956, Dundee and Rossman 1989, Ferguson and Landreth 1966) and progressively later as one moves north. Virginia populations normally breed from early May to July (Mitchell 1986), while breeding in North Carolina is usually well underway by April.

The males call from shallow water, often among scattered vegetation along the shoreline. Males that call continuously often expend a lot of energy inflating the lungs and vocal sacs, and most spend only a few days at the breeding site (Dodd 2013). In New Jersey, for example, Given (2002) found that chorusing males spent an average of only 3 days at the breeding site (range of 1-15 days). Females are attracted to calling males and tend to choose relatively large males as mates. Call characteristics such as the dominant frequency are used to distinguished males by size (Sullivan et al. 1996). At some sites relatively large males will select cooler calling sites than smaller males. This alters their voice since call characteristics are temperature-dependent (Zweifel 1968), and makes them sound larger than they actually are to females (Dodd 2013, Fairchild 1981).

The males usually greatly outnumber females at the breeding sites on any given night, often by 10:1 or more (Breden 1988, Ferguson and Landreth 1966, Green 2013). Females that enter breeding sites and are moving towards calling males are often intercepted and amplexed by non-calling satellite males or other males along the way. Amplexus is axillary or supra-axillary, depending on the size of the female. Once amplexed, the females select shallow, warm sites to lay their eggs.

Reproductive Mode: Each female deposits her eggs in one or two continuous, gelatinous strings and the amplexed male fertilizes them externally as they are laid. Each string has a singular tubular membrane with no intercellular partition between adjacent eggs. The ova are black above, tan to yellowish below, and about 1–1.5 mm in diameter. Each ova is surrounded by a single jelly envelope, and there are around 17 to 25 eggs per 25 cm of string length (Dodd 2013). Females typically deposit the egg strings in tangled masses around vegetation and debris in shallow water. The embryos develop rapidly and hatch within 2-7 days depending on the prevailing weather and water temperatures.

Clutch size is positively correlated with female body size (Green 2015) and can range from a few thousand to 16,000 eggs or so (Dodd 2013, Wright and Wright 1949). Clutches of Arkansas specimens that were examined by Trauth et al. (1990) varied from 3,067-15,618 eggs and averaged 8,175, while specimens from Virginia ranged from 2,662–7,742 and averaged 4,578 eggs (Mitchell and Pague 2014). Green (2015) reported that females at a study site in southern Canada laid from 1,998-7,200 eggs, with an average of 4,443.

Aquatic Life History: Growth rates are temperature-dependent and the hatchlings and larvae often concentrate in shallow water near shorelines on sunny days to feed in warm water. They retreat to deeper waters at night where temperatures are generally warmer than in the shallows. The diet is poorly documented, but the tadpoles presumably filter-feed on detritus, algae, and other food that is suspended in the water column, and eat filamentous algae, blue-green algae, periphyton, diatoms and the soft tissues of decaying plants. They tend to be benthic feeders and when concentrated along shorelines can work as a group to stir up food material. Breden et al. (1982) found that tadpoles in Indiana populations showed a weak tendency to aggregate and orient by size, although tadpoles of different sizes commonly mingled with each other.

Growth and developmental rates depend on prevailing conditions such as water temperatures, food quality and quantity, and the densities of competitors. The larval period can last anywhere from 21-60 days and the larvae reach a maximum length of around 21 mm TL (Dodd 2013). Most metamorphs vary from 7-15 mm SUL. Some of the reported average values for metamorphs include 7.2 mm SUL in Mississippi (Ferguson 1960), 9.0 mm in Indiana Dune populations, and 10.7 mm SUL for other Indiana specimens (Labanick and Schlueter 1976). Metamorphosis typically occurs between mid-June and mid-August but varies depending on the location and when the eggs are deposited seasonally. It typically occurs over a period of only a few weeks at any given site (e.g., Breden 1988). Most hatchlings do not survive to metamorphosis, presumably due to losses from competitors, predators, diseases and parasites. Survivorship from hatching to metamorphosis was approximately 12% based on numbers provided by Breden (1988).

Terrestrial Life History: The toadlets often remain close to shorelines for a week or more after metamorphosing before dispersing away from the breeding sites (e.g., Clarke 1974a). Ferguson (1960) found that most dispersal in a Mississippi population was by juveniles, with the adults living sedentary lives. Similarly, Breden (1988) studied a series of dune ponds along the Lake Michigan shoreline and found that most dispersal away from the natal ponds occurred during the first year of life. Subadults and sexually mature individuals dispersed far less. Data for toads that were marked at metamorphosis and recaptured as adults indicate that only around 50-70% of the metamorphs returned to their home ponds as adults. The remainder moved to other sites to breed, in one case up to 2 kilometers from the home pond. Mortality rates were highest during the first year of life, and Breden (1988) estimated that the probability of a hatchling surviving to become an adult was only 0.1%. Despite the high larval and juvenile mortality, survival to sexual maturity was sufficient to maintain a robust adult population due to the large clutch sizes of the females.

Growth in length is rapid during the first year, then slows thereafter. Toads in Breden's (1988) populations metamorphosed in July when they averaged 9.0 mm and grew to 47 mm by September. They reached an average of 60 mm at the end of their second fall, when most were sexually mature. Breeding occurred for the first time the following year. Most individuals in a population in Ontario also required two years to reach sexual maturity, with some requiring only one and others three years (Green 1997, Kellner and Green 1995). At least some males and females studied by Clarke (1974b) in Connecticut became sexually mature the second autumn after metamorphosis and bred for the first time the following year.

Middleton and Green (2015) found in their long-term studies of a population in Canada that individuals live no longer than 5 years. Annual mortality is high at all life stages, and the mean age over the course of a 17-year study averaged only 2.31 years for males and 2.44 for females. Only a small percentage survived for > 3 years, which indicates that most individuals breed only once during their lifetime. Hulse et al. (2001) found that males in Pennsylvania become sexual maturity at 48–50 mm SUL versus 57–60 mm SUL for females.

The juveniles commonly disperse hundreds of meters from their natal ponds and the adults often undertake long migrations to and from the breeding sites. In Michigan, Stille (1952) estimated that some adults migrate around a mile (1,609 m) to and from the nearest breeding site. Once they reach their summer feeding grounds, the adults are relatively sedentary and tend to remain within small home ranges. They typically remain in hiding during the day and forage at night. During the day they either burrow (Boenke 2011) or find shelter in mammal burrows, old tree root channels, under logs, leaf litter and other surface debris, or in grass clumps and other vegetation (Dodd 2013). Although the adults in many populations are relatively sedentary, Stille (1952) found that individuals made periodic movements from their diurnal retreats on sand dunes to the shores of Lake Michigan at night where they fed. These involved moving 60-215 m between the resting and foraging sites. Boenke (2011) found that they also show high site fidelity to daytime retreats after moving to the lake shoreline at night.

Ferguson (1960) marked adults in Mississippi that fed beneath a series of street lights and found that almost all of 100 marked individuals remained at the same light over a 5-month summer activity period. Clarke (1974a) found that the adults in a Connecticut population were strictly nocturnal and tended to be most active for the first few hours after dark, particularly on cloudless nights when temperatures dropped quickly after sunset. The average distances between captures varied from 22-32 m during a three-year study. These and other observations suggest that adults in most populations have relatively small home ranges. Ferguson (1963) experimentally displaced toads and found that they will readily return to either breeding ponds or their home ranges, particularly when displacement distance are less than a few hundred meters. This implies that breeding adults are capable of returning to their home ranges after leaving the breeding ponds.

The juveniles and adults are active throughout the warmer months of the year. Individuals in the southernmost populations may be actively nearly year-round, while those in northern populations may be active for only 5-6 months of the year. They overwinter on land by burrowing underground below the frost line using their hind limbs to dig. Individuals have often been found 10-50 cm below the ground surface (Dodd 2013).

The juveniles and adults tend to be sit-and-wait predators, but often make short movements in search of prey as they hop about at night. Numerous dietary studies have been conducted that are summarized by Dodd (2013). This species is a generalist, gape-limited predator that feeds on a wide variety of prey, particularly insects. Klimstra and Myers (1965), for example, found members of 11 insect orders and 67 families in their examination of 497 specimens from Illinois, with beetles, ants, lepidopterans and spiders particularly common in the diet. In addition to insects, the adults take a variety of other taxa such as centipedes, harvestmen, sowbugs, molluscs, and annelids. The juveniles also are generalists, but take smaller prey such as ants, mites, flies, collembolans and aphids that reflect gape limitations. Toads are visually oriented predators that are attracted to moving objects, which likely reflects the underrepresentation of certain groups such as snails in the diet.

General Ecology

Population Ecology: Local populations can vary in size from a few individuals to several thousand adults (Breden 1988, Ferguson 1960, Ferguson and Landreth 1966, Green 1997). Population size often varies substantially across years which likely reflects the short life expectancy of metamorphs and the production of large numbers of juveniles in favorable years. A population that was studied by Green (1997) varied from a low of only 12 breeding males in one year to between 229 and 294 males in three other years. Greenberg and Green's (2013) long-term tracking of a population in Canada show that fluctuations occur across years in a density-dependent manner. The adults are not territorial so density-dependent regulation likely occurs during the larval stage.

Many populations use clusters of local breeding ponds (e.g., Breden 1988), and appear to have such high rates of movements between ponds that there is little metapopulation organization at the local scale (Dodd 2013, Smith and Green 2005). Ferguson (1963), for example, noted that 14 of 135 marked animals in Mississippi shifted to another breeding site that was 389 m away. Most of the population studies of Fowler's Toad have been conducted from the northern portion of the range and detailed life history studies of southern populations are needed, including in North Carolina.

Community Ecology: Fowler's Toad larvae co-occur with a variety of predators and potential competitors, but studies of how competition and predation organize these communities are scant. Lawler and Morin (1993) examined interactions between the Spring Peeper and Fowler's Toad in artificial ponds and found that the order of arrival of species to ponds can affect competitive outcomes. Toad tadpoles had the greatest adverse impact when they were experimentally added to ponds before Spring Peepers were added.

Adverse Environmental Impacts

Habitat Fragmentation: Fowler's Toad appears to be tolerant of habitat fragmentation and is common in many areas of the Piedmont where landscapes are highly fragmented.

Effects of Introduced Species/Induced Increases of Native Species: Populations of Fowler's Toad have been impacted by the spread of invasive plants and the expansion of the range of native species in association with habitat disturbance. Greenberg and Green (2013) documented a sustained downward trend of a population at their study site in Ontario that was associated with the spread of the invasive Common Reed (Phragmites australis) in marshes that are breeding sites for the toads. Although this species is native to North America, a rank, invasive form has been introduced (Phragmites a. australis) that can form monocultures in marshes and convert the shallow, open water used by toads for calling and egg laying into dense thickets of poor quality.

Human disturbance of the landscape in association with population growth in Texas, Louisiana, and Mississippi are adversely affecting Fowler's Toad. The Gulf Coast Toad (Incilius nebulifer) is a native species that thrives in highly disturbed and urbanized settings. It appears to have expanded its range northward in recent decades, and Fowler’s Toad has undergone concommitant declines where the Gulf Coast Toad has proliferated. This likely reflects both hybridization with this species, which can produce partially inviable offspring, and the fact that A. fowleri larvae are inferior competitors (Dodd 2013, Vogel 2007, Vogel and Pechmann 2010).

Status in North Carolina

NHP State Rank: S5

Global Rank: G5

Environmental Threats: Populations in North Carolina appear to be tolerant of significant landscape disturbance and are often found in fragmented, suburban environments in the Piedmont (Gooch et al. 2006). Jones and Tupper (2015) noted that populations in Maryland and Virginia are in decline, and that landscapes that are most favorable for this species contain only moderate amounts of deciduous forest (< 50%), few hay crops (<35%), relatively little urban development (< 25%), and low pesticide application rates. This species does poorly in highly urbanized areas, but tolerates suburban development reasonably well. Countless thousands of Fowler's Toads are killed on roads each year (e.g., Timm and McGarigal 2014) and the ever increasing traffic volume on North Carolina's roads will continue to adversely affect this and many other native amphibians. This species has undoubtedly benefitted from the thousands of farm ponds that have been constructed in North Carolina.

Status Comments: Fowler's Toad is common in the Piedmont of North Carolina (e.g., Gooch et al. 2006), but is uncommon and spottily distributed at lower elevations in the mountains. Populations appear to have declined in recent decades in the central and northern mountains where there are numerous historical records but almost no recent records. Populations in the Coastal Plain may also be in decline based on the paucity of recent records of this species in many areas (e.g., iNaturalist). Jones and Tupper (2015) reported a 53% decline in Maryland and Virginia populations from 1999 to 2012. These may in part be due to changes in forest successional stages.

Photo Gallery for Anaxyrus fowleri - Fowler's Toad		19 photos are shown.
	Recorded by: Erin Dailey Durham Co.	Recorded by: Simpson Eason Granville Co.
	Recorded by: Steve Hall, Pat Coin, David George, and Mark Basinger Chatham Co.	Recorded by: Salman Abdulali Pitt Co.
	Recorded by: David George Chatham Co.	Recorded by: Abaigh Robinson Orange Co.
	Recorded by: James kelley Wayne Co.	Recorded by: James kelley Wayne Co.
	Recorded by: James kelley Wayne Co.	Recorded by: Savannah Hall, Dee Stuckey, and Steve Hall Orange Co.
	Recorded by: J. Mickey Stokes Co.	Recorded by: S. Dagenhart Dare Co.
	Recorded by: John Petranka Orange Co.	Recorded by: John Petranka Orange Co.
	Recorded by: Steve Hall and Dee Stuckey Orange Co.	Recorded by: Owen McConnell Durham Co.
	Recorded by: Steve Hall Orange Co.	Recorded by: Steve Hall Orange Co.
	Recorded by: Steve Hall Orange Co.

Anaxyrus fowleri - Fowler's Toad

Photo Gallery for Anaxyrus fowleri - Fowler's Toad

19 photos are shown.