Amphibians of North Carolina

Scientific Name:	Common Name:		Family (Alpha):

NC Records
Bufonidae Members:
Anaxyrus quercicus - Oak Toad

Taxonomy

Class: Amphibia

Order: Anura

Family: Bufonidae

Synonym: Bufo quercicus


Taxonomic Comments:
Species Comments:

Identification

Description: The Oak Toad is a miniature toad that is the smallest of any of the 19 species of North American Anaxyrus. The dorsal ground color is usually gray, but it can be brown or nearly black in some specimens. A conspicuous, narrow, mid-dorsal stripe extends from the snout to the urostyle that is typically white or cream-colored, but sometimes light red or orangish. There are two to five pairs of dark blotches on either side of the mid-dorsal stripe, and an irregular broader region of blackish pigmentation that extends from the eyes along the lower sides. This can be represented as either a series of blackish blotches that sometimes form an irregular and often broken band, or simply a diffuse band of dark pigmentation along the lower sides. Numerous granular tubercles that are often reddish to orangish are present on the upper surfaces of the legs and the dorsal and dorsolateral regions of the body. The reddish-orange tubercles are also present on the undersurfaces of the feet (Beane et al. 2010). The cranial crests are low, and the parotoid gland is large relative to body size (Dodd 2013). The belly is white with mottled dark pigment ventrolaterally, and the groin is sometimes tinged with yellow. The male has a dark oval vocal sac that inflates to extend well above the head.

The adult males vary from 19-32 mm SUL (snout to urostyle length; a close approximation of SVL) and the females from 21-35 mm SUL (Dodd 2013). Amplexed males that Wilbur et al. (1978) collected at three eastern North Carolina sites were the same size as the females at one site and 2.2–2.7 mm smaller than the females at two other sites. The males averaged 28 mm SUL, compared with 30.2 mm SUL for females. Adult males also averaged smaller (28.7 mm) than adult females (31.5 mm) in a series of ponds that were monitored by Greenberg and Tanner (2005) in northern Florida.

The larvae are dark with diffuse lighter blotching. Dark pigmentation covers the upper portion of the tail musculature, but the ventral portion is unpigmented. The dorsal tail fin is lightly spotted in young larvae, but becomes increasingly pigmented with age. Larvae reach a maximum length of 19–28 mm TL (Dodd 2013).

Vocalizations: The advertising call consists of a series of high-pitched continuous peeps that sounds like a baby chick peeping, with about 2-3 peeps per second.

Technical Reference: Dodd (2013)

Online Photos: Google iNaturalist

Observation Methods: The adults are diurnally active and can be found within a hundred meters or so of the breeding ponds. The easiest way to document local populations is to listen for calling males following heavy summer rains. They are occasionally seen of roads on rainy nights.

AmphibiaWeb Account

Distribution in North Carolina

Distribution Comments: The Oak Toad is associated with Coastal Plain habitats from southeastern Virginia southward through the Carolinas and Georgia to all of Florida, including the Florida Keys. The range extends westward from Florida along the lower Gulf Coast through Alabama and Mississippi to southeastern Louisiana. A disjunct is present in central Alabama in the Coosa Valley.
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: Anaxyrus quercicus has a biphasic life cycle and requires both suitable wetlands for breeding and terrestrial habitats for the juveniles and adults. The juveniles and adults typically live in dry, open uplands of the Coastal Plain. The preferred habitats have sandy, friable soils and extensive areas of low vegetation, grasses, and downed logs that provide cover and moist microhabitats (Dodd 2013). Heavily shaded ponds in hardwood settings are generally avoided. Greenberg and Tanner (2005) collected more adults in habitats that were previously invaded by hardwoods after fire suppression than in fire-maintained savanna-like sandhills with a relatively dense cover of wiregrass. The former sites were being burned at 1-4 year intervals as part of a restoration project, but wiregrass had not become well established at the sites relative to the pine savannas.

The larval period usually last < 2 months and the adults most commonly breed in a variety of shallow, seasonal habitats that typically lack fish. Baber and Babbitt (2003) found that native fishes will eat A. quercicus tadpoles, but that predation rates were lower than the tadpoles of other seasonal pond species that were tested. Thus, they appear to have limited chemical defenses against predatory fish. Small natural seasonal ponds are commonly used, but the adults will also breed in flooded fields, borrow pits, cut-over lands with flooded depressions, and grass and sedge-filled ditches (Dodd 2013, Eason and Fauth 2001, Gunzburger et al. 2010, Krysko et al. 2019). Although densely vegetated sites with thick leaf litter are rarely used, populations sometime use cypress domes and hammocks (Punzo 1995). Although this species prefers seasonal habitats, it will occasionally use sites that hold water year-round.

In North Carolina, populations are associated primarily with pine savannas, flatwoods, and pine-scrub oak sandhills. They also occur at a few sites on the northern Outer Banks, but are much more frequent on the barrier islands of South Carolina (Beane et al. 2010). All of these habitats have a fairly open canopy of pines and xerophytic oaks, and possess an extensive herbaceous ground cover that is dominated by grasses. Fire is a key habitat factor in maintaining these communities. The ashy gray coloration of the Oak Toad, along with its prominent pale dorsal stripe, provides excellent camouflage on recently burned substrates with scattered Longleaf Pine needles.

The adults breed in seasonal or semipermanent wetlands in sunny or partially shaded habitats. Commonly used habitats include rain pools, depressional ponds, Carolina bays, borrow pits, flooded fields, roadside ditches, and freshwater depressional ponds behind dunes.

Environmental and Physiological Tolerances: The larvae are tolerant of acidic, nutrient-poor waters but appear to mature more quickly in depressions that have been recently burned, probably due to the greater alkalinity provided by the ash deposits (Noss and Rothermel 2015).

Adaptations to Natural Disturbances: The Oak Toad occurs in habitats maintained by frequent fire and is often absent or rare in habitats that have only a moderate fire frequency regime (Darracq et al. 2016). The adults probably escape fire by burrowing, but observations of burrowing with an approaching fire have not been observed.

Biotic Relationships: The breeding sites are typically ephemeral and isolated from nearby streams. They normally lack fish and also tend to have relatively few aquatic invertebrate predators such as odonates that have long larval stages. Native fishes will eat the tadpoles, but predation rates are lower than those of other seasonal pond species such as the Eastern Narrow-mouthed Toad (Baber and Babbitt 2003). Aquatic invertebrates such as diving beetles and odonates can also be effective predators on the tadpoles (Noss and Rothermel 2015). Despite having toxic skin secretions, there are several records of the adults being attacked -- and in some cases killed --by vertebrate predators, including raccoons, crows, hog-nosed snakes, garter snakes, gopher frogs, and marine toads (AmphibiaWeb, 2021).

See also Habitat Account for Longleaf Pine Woodlands with Isolated Pools

Life History and Autecology

Breeding and Courtship: The adults mostly mate and lay eggs during the warmer months of the year, typically beginning in April or May and continuing through September or October. Breeding bouts often occur after heavy rains fill or enlarge the breeding pools (Greenberg and Tanner 2005, Wright and Wright 1949). Breeding frequently occurs through late October in southern Florida. There are also records of breeding occurring as early as late February in northern Florida and as late as November in Georgia (Dodd 2013, Duellman and Schwartz 1958, Einem and Ober, 1956, Jensen et al. 2008). Peak seasonal activity normally occurs during the late-spring and summer months (June-September), but can occur at any time until cooler weather begins to arrive in the autumn (e.g., Babbitt and Tanner 2000). Greenberg et al. (2017) conducted long-term tracking of eight populations in east-central Florida and found that the adults bred from May through October, with a seasonal peak between June and August. The juveniles emerged from ponds from June through December. Breeding in North Carolina also occurs during the warmer months of the year, typically from May through August.

Heavy rains often trigger the adults to move from nearby uplands to the breeding sites. The males normally call during the day in or at the edge of shallow water in flooded fields, ditches, seasonal ponds, and other suitable breeding sites. Calling can occur from both exposed sites and beneath cover such as grass clumps. The high-pitched advertisement call is distinctive and resemble a baby chick that is peeping.

Breeding tends to be somewhat synchronized following heavy rains and males often gather in small choruses. When a gravid female approaches a male, he amplexes her dorsally just behind the front legs. Egg laying ensues shortly thereafter. Wilbur et al. (1978) found that larger males are more successful in amplexing a female, but it is uncertain if this reflects females choosing larger males, or larger males outcompeting smaller males for mates. Greenberg and Tanner (2005) found sex ratios in drift fence captures to be 2.3:1 in a group of ephemeral ponds in northern Florida, which suggests that males may compete for a limited number of females.

Reproductive Mode: Females deposit their eggs in small bead-like strands or bars that have 2-8 eggs each. These are sometimes laid in small clusters, and are either deposited on the bottom substrate or attached to support structures such as branches and grass blades that are in shallow water (Dodd 2013, Volpe and Dobie 1959, Wright 1932). The freshly laid ova are black or brown above and white to yellow below and vary from 0.8 to 1.1 mm in diameter. Each egg is surrounded by a single jelly envelope that is 1.2-1.4 mm in diameter and the adjoining eggs are connected by a surrounding thin jelly membrane to produce a short strand (Dodd 2013, Volpe and Dobie 1959, Wright 1932). During a reproductive bout the male draws his legs up and fertilizes several short strands as they are extruded. He then relaxes his legs for one to two minutes before repeating the process. The amplexed pair then moves to another site close by and deposits more short strands of eggs (Dodd 2013). Clutch sizes based on counts of ovarian eggs vary from around 500 to >700 eggs, which is far fewer than our other native toads. Wilbur et al. (1978) reported that both the clutch size the average egg diameter were independent of female body size in North Carolina populations. The embryos develop rapidly and typically hatch within 24–80 hours after the eggs are laid.

Aquatic Life History: Very little is known about the larval life history. The larvae filter-feed on detritus, algae and their associated microorganisms (Dalrymple 1990). Fully grown larvae reach a maximum length of around 18–19 mm. The larval period is brief and last 4–8 weeks, with the newly metamorphosed froglets varying from 7–8.9 mm SUL (Dodd 2013, Volpe and Dobie 1959, Wright 1932). The larvae are preyed upon by fishes and aquatic invertebrates, although most seasonal breeding sites lack the former unless they are connected to permanent sites during heavy flood events. Noss and Rothermel (2015) found that survival of larvae in experimental enclosures that were colonized by predaceous beetles and odonates was reduced by > 90% relative to enclosures that were not colonized.

Terrestrial Life History: The juveniles disperse away from the breeding sites after metamorphosing and generally appear to be more active during the late summer and early autumn (Dodd 1994). Movements away from the natal ponds often occur during bouts of rainy weather (Greenberg and Tanner 2005). Hamilton (1955) noted that juveniles in southern Florida that he collected were often engorged with food and grew rapidly, except during the coldest winter months when they were inactive. Individuals grew 2-4 mm per month during the spring months, and males were estimated to become sexually mature one year after they metamorphosed. Females were believed to require an additional year before they bred for the first time. The adults appear to be short-lived. Dodd (1994) marked over 400 adults at a Florida site over a 5-year period and never recaptured individuals more than two years after they were marked. Based on mark-recapture data, Greenberg and Tanner (2005) concluded that most adults only live two years, with a very small percentage surviving for up to four years.

Both the juveniles and adults subsist on small invertebrates. Ants are particularly important prey (Hamilton, 1955; Duellman and Schwartz, 1958; Punzo, 1995), but many other invertebrates are consumed. Hamilton (1955) found that 94% of 200 specimens that they examined from Florida and Georgia contained ants of several species. Beetles were the second most important group based on frequency of occurrence (67% of specimens), followed by spiders, mites, hemipterans, aphids, lepidopteran larvae, molluscs, dipterans, orthopterans, millipedes, centipedes, collembolans, and pseudoscorpions. Punzo (1995) examined specimens from the Florida Panhandle and found that ants were the most important prey based on frequency of occurrence, followed by spiders, carabid beetles, and termites. Mites and collembolans were not eaten by adults, but were important prey of the juveniles. This suggests that the adults are size-selective feeders and ignore very small prey. The juveniles also fed extensively on spiders, ants, and termites.

Oak toads are active on the ground surface during the warmer months of the year. They generally remain underground in burrows or beneath surface cover such as logs or slab of pine bark during cold weather (Hamilton 1955, Wright and Wright 1949). Dodd (1994) noted that the juveniles are more active in late summer and early autumn, while the adults are most active during the summer months.

General Ecology

Population Ecology: Factors that regulate local population sizes are poorly resolved. Oak toads often exploit small wetlands and local breeding populations commonly consist of fewer than 100-150 individuals (e.g., Greenberg and Tanner 2005). It is uncertain to what extent local populations are organized as metapopulations, but it is likely that dispersal between populations is high where clusters of local ponds exist in close proximity (Dodd 1994).

Greenberg and Tanner (2005) monitored a group of eight ponds in northern Florida over 10 years and found that -- despite significant fluctuations in adult catches annually -- all eight populations remained stable across the study period. This happened even though juvenile recruitment was very low during most years and comprised only 7.8% of the entire catch of 4,076 toads. Most marked adults were recaptured in their home ponds, but a small percentage moved between ponds. One individual moved an estimated 469 meters to another pond. The authors were unable to mark the tiny metamorphs, so it was uncertain to what extent the juveniles moved between ponds. Overall, they found little support for metapopulation organization due to the very low recruitment of juveniles across most ponds in most years. Their enigmatic results where there were stable adult populations across years despite little juvenile recruitment has yet to be fully explained, particularly given that most individuals do not live for more than two years.

Adverse Environmental Impacts

Habitat Loss: Oak Toads appear to be in decline in many areas of the range. Carr (1940) described this species as being so common in central Florida that one could drive through the area during the breeding season and never find a place to stop where the males were not calling. Florida's population was around 2 million in 1940 versus 22 million today, and the widespread increase in development and large-scale agricultural activities have resulted in the drainage and degradation of countless breeding sites (e.g., Guzy et al. 2012). Similar situations have occurred throughout the Southeast in association with rapid growth and development in the Sun Belt. Because the breeding sites are typically small and seasonally ephemeral, they received little or no legal protection and are vulnerable to habitat destruction and fragmentation. The juveniles and adults depend on fire-maintained communities, and many terrestrial habitats have been degraded or lost due to the lack of prescribed burns. Populations of this species are still very common in Florida, but those farther north appear to have suffered significant declines except in areas where fire-dependent communities such as Long-leaf Pine savannas are being maintained.

Status in North Carolina

NHP State Rank: S2

Global Rank: G5

Status in North Carolina: SR

Environmental Threats: Populations in North Carolina and elsewhere have undergone significant declines in recent decades (Beane et al. 2010), in part due to habitat loss or degradation. Other factors such as disease may have played a role, but evidence for this is lacking. The Red Imported Fire Ant (Solenopsis invicta) may have adversely affected this species since the ants can both deplete the invertebrate prey base and attack the juvenile and adults. Oak toads do best in fire-maintained systems and is most common today in North Carolina in the Sandhills and coastal regions where prescribed burns occur at frequent intervals. We have many historical county records in the Coastal Plain where populations have not been rediscovered in recent years.

Photo Gallery for Anaxyrus quercicus - Oak Toad		9 photos are shown.
	Recorded by: Mark Shields, Hunter Phillips Onslow Co.	Recorded by: Morgan Freese New Hanover Co.
	Recorded by: Bockhahn and Kittelberger Washington Co.	Recorded by: C. Edwards New Hanover Co.
	Recorded by: Morgan Freese Dare Co.	Recorded by: Mark Shields Carteret Co.
	Recorded by: M. Gosselin Dare Co.	Recorded by: M.Windsor Dare Co.
	Recorded by: M.Windsor Dare Co.

Anaxyrus quercicus - Oak Toad

Photo Gallery for Anaxyrus quercicus - Oak Toad

9 photos are shown.