Amphibians of North Carolina
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Ambystoma tigrinum - Eastern Tiger Salamander

Taxonomy
Class: Amphibia Order: Caudata Family: Ambystomatidae
Taxonomic Comments: The genus Ambystoma consists of 32 currently recognized species that are found in North America and Mexico. The terrestrial adults have stout bodies and legs, widely spaced eyes, and well-developed costal grooves.
Species Comments: The Tiger Salamander (Ambystoma tigrinum) was traditionally treated as a single, wide ranging species with as many as eight subspecies. These range throughout much of the United States and west-central Canada, and southward to the southern Sierra Madre Occidentalis in Mexico. It is now treated by most authorities as a species complex that contains three species. These include A. californiense, A. mavortium, and A. tigrinum (sensu stricto). The California Tiger Salamander (Ambystoma californiense) is a genetically distinct species that is geographically isolated from the other members of the complex. The Western Tiger Salamander (A. mavortium) is found in the western and central North America and northern Mexico and contains five subspecies that exhibit marked geographic variation in morphology, behavior, and life history patterns. The Eastern Tiger Salamander (Ambystoma tigrinum) is the third member and is restricted to eastern North America. Some authorities treat A. mavortium and A. tigrinum as a single, polytypic species. Here, we consider the Eastern Tiger Salamander (A. tigrinum) to be a separate species from the Western Tiger Salamander (A. mavortium).
Identification
Description: The Eastern Tiger Salamander (Ambystoma tigrinum) is a large, robust Ambystoma with a broad, flattened head and widely separated eyes. The largest adults can approach 25 cm in length. The coloration and patterning are variable, but generally consist of dull yellow or yellowish-brown crossbands and rounded blotches on a dark brown or blackish background. Rounded blotches prevail on the body, while the tail often has crossbands. The dull yellow to yellowish-brown blotches may be so extensive on some individuals that the overall appearance is that of a dull yellow animal with an overlaying reticulated meshwork of dark brown or blackish lines. The venter is yellowish with darker blotches. The adult male has a laterally compressed tail and develops a swollen cloaca during the breeding season. The female has a more rounded tail that is proportionately shorter. Gilled adults are rare in A. tigrinum and have only been found in Michigan (Petranka 1998).

The hatchlings are pale brownish to greenish brown above and are typically 10-18 mm long. The venter is pale yellow to whitish and unmarked. The hatchlings sometimes have paired blotches along the dorsum and have a dorsolateral row of light spots. The older larvae have broad heads with rounded snouts, conspicuous bushy gills, and broad dorsal fins that extend forward before terminating near the base of the gills. The toes are broad at the base and pointed at the tips. The larvae grow quickly and soon exceed the maximum size of other Ambystoma species that share breeding ponds. The older larvae are white beneath and dull-green to dusky colored above. They have varying levels of indistinct blackish and dull yellowish mottling on the tail and dorsum of the body that tends to be lost with age. Juveniles begin to acquire the adult coloration within one month after transforming.
Technical Reference: Petranka (1998)
Field Guide Descriptions: Beane et al. (2010)
Online Photos:    Google   iNaturalist
Observation Methods: The adults can be found beneath cover objects in and around breeding pools during the breeding season. Larvae have a variety of foraging strategies that include floating in the water column at night, resting motionless on the bottom substrate and lunging at prey that approach, and actively crawling through vegetation or bottom debris in search of prey. They can be observed during the day and night, but are most easily collected by dip-netting.
AmphibiaWeb Account
Distribution in North Carolina
Distribution Comments: This species is distributed across much of the eastern US, as well as southeastern Manitoba and extreme southern Ontario. In the US the range extends from New York and New Jersey southward to northern Florida, and westward to eastern Texas, southeastern Oklahoma, eastern Kansas, eastern Nebraska, and the eastern Dakotas. Populations are absent from most of the Appalachian Mountains and Piedmont, and are typically found in areas with friable soils that allow the adults to burrow. This species is patchily distributed along the East Coast, with several populations being relatively isolated from the more continuously distributed populations in the South and Midwest. In North Carolina, most populations occur in the Sandhills and vicinity, and only rarely in the extreme eastern Piedmont. Molecular studies indicate that North Carolina populations have been geographically isolated from more southern populations in South Carolina and Georgia for 0.4-1 million years (Church et al. 2003).
Distribution Reference: Petranka (1998); Beane et al. (2010).
County Map: Clicking on a county returns the records for the species in that county.
GBIF Global Distribution
Key Habitat Requirements
Habitat: The Eastern Tiger Salamander occurs locally at sites with sandy or otherwise friable soils and fish-free breeding sites. The adults typically breed in seasonal and semipermanent ponds, but will also use permanent ponds that lack predatory fish. The terrestrial juveniles and adults actively dig underground burrows that they use as shelters and feeding sites, and generally require habitats with soft substrates that allow them to burrow. They typically live in forested sites such as alluvial forests, xeric and mesic hammocks, and coastal pine forests, but also use open fields, prairies, and pastures, particularly in the Midwest. Breeding normally occurs in fish-free habitats, and commonly in seasonal wetlands. Commonly used habitats include depressional ponds, marshes, swamps, vernal ponds, sinkhole ponds, and artificial habitats such as borrow pits, retention ponds, and farm ponds (Beane et al. 2010, Krysko et al. 2019, Petranka 1998).

In North Carolina, almost all populations are associated with Longleaf Pine dominated habitats that surround depression ponds and Carolina bays. In the eastern Piedmont, however, they occupy bottomland hardwoods and breed in isolated pools within the floodplain or in adjoining areas that are now converted to pastures.
Biotic Relationships: The larvae live in fish-free habitats and are voracious predators that quickly grow to a large size. In many respects, they fulfill the ecological niches that small predatory fishes have in more permanent habitats. In addition to consuming a wide variety of invertebrate prey, the older larvae cannibalize, and also feed on the larvae of frogs, newts, and other Ambystoma species. The hatchlings undoubtedly suffer significant mortality from invertebrate predators such as dragonflies and dytiscid beetle larvae. The Eastern Newt is an important predator on the eggs. In North Carolina, egg predation by newts can result in close to 100% mortality, and can be sufficiently high to virtually exclude A. tigrinum from otherwise suitable breeding sites (Morin 1983).
See also Habitat Account for General Forests with Isolated Pools
Life History and Autecology
Breeding and Courtship: This species breeds from November through May in different regions of the eastern US. In the northern part of the range, breeding in non-coastal regions typically occurs from late-February through April. In coastal regions in New Jersey breeding may begin as early as January (Petranka 1998). Populations in the southeastern US breed in both autumn and during the winter months. Depending on yearly rainfall patterns and pond hydrology, breeding in North Carolina can begin as early as November and continue through mid-March (Beane et al. 2010, Morin 1983).

The adults migrate to ponds at night during or immediately following rainy weather. At an Indiana site, males arrive at a breeding pond at about the same time as females and adults remain from 10-29 days. Most females at this site breed annually (Petranka 1998). At the Savannah River Site in South Carolina, the males arrive at the breeding ponds 2-8 weeks before the females (Semlitsch 1983). Peak migrations to the ponds occur in January and February, while peak migrations from the ponds occur from January through March. In South Carolina, breeding activity is positively correlated with rainfall, and few or no females migrate to ponds during years with low rainfall.

Once they reach the ponds, the adults tend to gather in widely dispersed groups of 2-3 individuals and court. When courting, the male moves along the length of the female while nudging, swinging his head, and lifting the female's venter. The male then pushes his snout against the lateral or ventral portions of the female's body and shoves her several centimeters to a meter. The male then engages in a tail-nudging walk in which he moves a short distance from the female while tapping the tail on her dorsum. The female moves forward and contacts the male's cloaca with her snout, and the male moves forward with his tail raised and deposits a spermatophore. The female follows, moves forward, and inserts the spermatophore into her cloaca. If the female remains responsive, the male may continue moving forward while monitoring the female's position with his tail and deposit additional spermatophores (Arnold 1976).

Males typically outnumber females in breeding populations and compete for females when courting. A male will often engage in sexual interference or sexual defense by shoving a female away from a second male. A male may also intrude between a female and a rival male, and, while mimicking the female's behavior, cover up the rival's spermatophores with his own (Arnold 1976, Petranka 1998). A male may deposit from 8-37 spermatophores in a single night.
Reproductive Mode: Within a day or two after courting, the females deposit their eggs in gelatinous masses on twigs, weed stems, and other support structures in the ponds. Each female may lay 400 eggs or more and deposit numerous egg masses. The freshly laid egg masses are firm, globular or oblong in shape, and average about 55 x 70 mm. By the end of the embryonic period the masses swell to a much larger size and become very loose and flimsy. The ova are 2-3 mm in diameter and are surrounded by three envelopes (Petranka 1998). An egg mass may contain as few as five to as many as 150 or more eggs, but most have between 30-50 eggs. A series of egg masses from North Carolina had 13-52 eggs per mass (Morin 1983). Length of the incubation period varies depending on weather patterns, local pond conditions, and the seasonal time of oviposition. The embryos typically begin to hatch within 20-50 days after the eggs are laid. Embryos that were monitored in North Carolina required 29-36 days to reach the hatching stages (Morin 1983).
Aquatic Life History: The larvae are gape-limited predators and feed on a wide variety of aquatic organisms. The hatchlings and young larvae take very small prey such as cladocerans, copepods, ostracods, and chironomid larvae. Large larvae continue to feed on zooplankton, but also take larger prey, including amphibian eggs and larvae, and the eggs and larvae of conspecifics (Petranka 1998). In an Indiana population, prey items included chironomid larvae, clam shrimp, cladocerans, copepods, ostracods, rotifers, insects, water mites, amphipods, oligochaetes, gastropods, leeches, and American toad tadpoles (Sever and Dineen 1978). Wood Frog tadpoles and other Ambystoma larvae were major prey items in a Michigan study (Wilbur 1972).

The larvae grow rapidly and can reach 10 cm TL within 2-4 months. In the Midwest and northeastern United States, the larval period typically lasts 2.5-5 months, with most larvae metamorphose between June and August when 40-75 mm SVL (Petranka 1998). Premature pond drying in drought years can trigger early metamorphosis. The larval period in southern populations may be relatively long in situations where the adults breed during the autumn and the larvae overwinter. Larvae in a fall-breeding population in Louisiana grew to 56-90 mm TL by December and reached 60-125 mm TL by April (Dundee 1974).

In some instances, a small percentage of larvae that are in permanent ponds may overwinter and transform the following year at exceptionally large sizes. Larvae transform in June in the majority of populations in southern Illinois, but larvae in some ponds may overwinter and reach 17-21 cm TL by the following April (Brandon and Bremer 1967). Despite their large size, overwintering larvae at these sites were sexually immature. Although gilled adults are common in the closely related Western Tiger Salamander, they have only been found in a few Michigan populations of the Eastern Tiger Salamander (Petranka 1998). In North Carolina, the larvae grow rapidly and normally metamorphose in May through July when 70-120 mm TL (Beane et al. 2010). Premetamorphic survivorship is generally < 10% or lower, and catastrophic mortality from intense egg predation and premature pond drying occurs periodically. Researchers in New Jersey found that premetamorphic survivorship varied from 0-8.7%, with roughly 60% of the premetamorphic mortality occurring prior to hatching (Anderson et al. 1971).
Terrestrial Life History: The juveniles and adults live in forests or more open habitats that surround the breeding ponds. Very little information is available on adult habitat requirements or the distances that individuals disperse from the breeding ponds. The juveniles and adults can dig their own burrows and presumably spend much of their time in underground burrows that provide relief from the hot and often dry conditions that prevail in many areas of the range, as well as freezing winter conditions. Populations are generally restricted to sites with friable soils that allow individuals to burrow. Steen et al. (2006) tracked four adults in South Carolina and found that the adults move as far as 255 m from the breeding site.

The juveniles and adults feed on earthworms, insects, and other invertebrates, and the adults have even been found to eat young field mice in New York (Bishop 1941). The terrestrial juveniles grow rapidly and some become sexually mature in as little as two years in South Carolina, where the smallest adults at the Savannah River Site are 81-85 mm SVL (Semlitsch 1983). The annual production of metamorphs at this site ranged from 0-24 juveniles per female. Only 6 of 1041 juveniles that left one site returned to breed 2 years later, although 52 were observed during the third year.
General Ecology
Population Ecology: Factors that regulate the sizes of adult populations are poorly documented. Morin (1983) found that the Eastern Newt is an important predator on the eggs. Egg predation is so severe in some ponds in North Carolina that is appears to greatly reduce the size of the adult populations (Morin 1983). Long-term studies at the Savannah River Site in South Carolina indicate that the production of A. tigrinum juveniles is episodic (Pechmann et al. 1991, Semlitsch et al. 1996). At this site the larvae often suffered complete mortality from pond drying in years with low rainfall. The number of metamorphs produced per female was not significantly affected by the initial larval densities in the pond, and there was only weak evidence of negative interactions of A. tigrinum larvae with other salamander larvae that shared the pond. Thus, density-dependent regulation during the larval stage may not be as important in this species relative to other Ambystoma species where crowding sets a limit on the number of juveniles that exit the ponds.
Community Ecology: The larvae are important predators in fish-free ponds that are used as breeding sites. Because they grow faster and reach a larger size than other Ambystoma species, they can easily consume large insects, as well as the larvae of frogs, newts, and other Ambystoma species. Wilbur (1972) conducted experiments to determine the effect of A. tigrinum larvae on three other Ambystoma species that share ponds (A. laterale; A. tremblayi; A. texanum). He found that all three species have lower survival in the presence of A. tigrinum. Adding wood frog tadpoles decreased the survival of all three species, presumably because A. tigrinum grew sufficiently large after feeding on tadpoles to prey on congeneric Ambystoma larvae.

Brophy (1980) found very similar diets between A. tigrinum and Notophthalmus viridescens larvae that coexist in a pond in southern Illinois, which suggests that these species compete for food. Morin (1983a) used experimental communities established in cattle tanks to study community interactions of Ambystoma tigrinum larvae with anuran larvae that use seasonal wetlands in the Sandhills of North Carolina. Tiger salamander larvae were capable of completely eliminate assemblages of tadpoles in the tanks. it is uncertain to what extent this occurs in more complex, natural settings where microhabitats such as vegetated shallows may provide a degree of protection from this and other predators.
Adverse Environmental Impacts
Habitat Loss: Since European colonization, this and many other amphibians have experienced significant long-term declines associated with deforestation, urbanization, agricultural and silvicultural activities, industrialization, and the filling and draining of wetlands. Although A. tigrinum uses prairies and other open habitats in the Midwest, local populations on the Atlantic Seaboard appear to require both fish-free breeding sites and forested buffers around breeding ponds to support the juveniles and adults. Longleaf Pine forests with depression ponds and Carolina bays offer ideal habitats. Unfortunately, much of the Longleaf Pine forests in the Southeast have been destroyed since European colonization and replaced with tree farms or agricultural fields.

The loss of wetlands has also been substantial. From the 1950s–1970s wetland losses in the Southeast were greater than in any other region of the country, with a net annual loss of 386,000 ac/yr (Hefner and Brown 1985). In North Carolina approximately 51% of all wetland acreage on the Coastal Plain has been lost. Countless thousands of Carolina bays, pocosins and other depressional wetlands that served as primary breeding sites for the Eastern Tiger Salamander and other seasonal-pond breeders have been drained, filled, and converted to agricultural fields or commercial pine plantations (e.g., Bennett and Nelson 1991, Lundine and Trembanis 2021, Richardson 2003, Sharitz and Gibbons 1982). Although poorly documented, numerous A. tigrinum populations have undoubtedly been lost in North Carolina since European colonization. This species is now listed as threatened in the state.
Habitat Fragmentation: Much of the original forested landscape that blanketed the eastern US prior to European colonization has been converted into a patchwork of agricultural fields, residential homes, businesses, roadways, and isolated forested parcels. In the Coastal Plain, Longleaf Pine forests and their associated wetlands covered vast regions of the Southeast. Most of what was once the largest forest ecosystem in North America was subsequently destroyed, and many of the associated wetlands were filled in the process of making way for agricultural fields, tree farms, and urban development.

The extent to which the Eastern Tiger Salamander has been impacted by habitat fragmentation is not fully known. Local populations often survive in unforested habitats such as pastures or prairies in certain areas of the range, which suggests that this species can tolerate a significant degree of habitat disturbance. Ambystoma populations in general exhibit varying levels of metapopulation organization where a regional group of local pond populations are connected by the occasional movement of individuals between populations. Connectivity between local populations allows for the recolonization of ponds following local extinctions, and reduces the chance of a local population going extinct when a population is in decline. Many regional populations of the Eastern Tiger Salamander in the Southeast were undoubtedly organized as metapopulations prior to European colonization. Habitat fragmentation and the widespread destruction of wetlands has resulted in many local populations losing their connectivity with neighboring populations. The isolated populations that remain are vulnerable to local extinction and may ultimately be lost with time.
Status in North Carolina
NHP State Rank: S2
Global Rank: G5
Status in North Carolina: T
Environmental Threats: The continued loss of depressional wetlands and surrounding forests are the greatest threats to this species. Many remaining populations are also geographically isolated from nearest neighbors, lack genetic connectivity, and are at risk of future local extinctions.
Status Comments: Populations that have been documented in North Carolina are largely restricted to Carolina Bays and depressional wetlands in Longleaf Pine communities. Most are geographically isolated, with little or no dispersal occurring between neighboring pond populations. Small, isolated populations are vulnerable to local extinctions in the long run, and there is concern that many of North Carolina's remaining populations may be extirpated at some point in the future. This species is currently listed as Threatened in the state.
Stewardship: Populations are best maintained by having a series of local seasonal wetlands of varying hydroperiods within a matrix of forested habitat.

Photo Gallery for Ambystoma tigrinum - Eastern Tiger Salamander

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Recorded by: Jeffrey Neil McMillan
Cumberland Co.		Recorded by: Jeffrey Neil McMillan
Cumberland Co.
Recorded by: Kevin Metcalf
Scotland Co.		Recorded by: Jim Petranka
Scotland Co.