An ancient group of vertebrates, many of which are now extinct, amphibians first arose 360 million years ago from fishlike ancestors. Amphibians live on land or in freshwater, but not in brackish or salt water. In the United States, amphibians are most abundant in the Southeast; Alabama's temperate climate and its great variety of terrestrial and aquatic habitats accommodate a rich, diverse variety of native amphibian species. They are an integral and important component of Alabama's ecological web.
The word amphibian is derived from Greek roots meaning "double-life," because most amphibians live as aquatic animals during the larval stage and terrestrial animals during the adult stage; some salamanders, however, remain permanently aquatic. Amphibians typically breed once yearly. Similar to fishes, most amphibians deposit gelatinous egg masses in water or in very moist environments, such as rotting logs. After the eggs hatch, aquatic amphibian larvae typically do not closely resemble the adults' body form. Salamanders (Order Urodela or Caudata) are carnivorous both as larvae and adults. Frog and toad (Order Anura) larvae are generally herbivorous, but they will scavenge animal debris if acceptable plant matter is not available. After metamorphosis (or transformation), the adults of all amphibians become exclusively carnivorous. Unlike reptiles, amphibians do not possess scales, claws, horns, or rattles, and their eggs do not have shells. Like reptiles and fishes, however, the temperatures of amphibians' bodies are determined by the temperatures of their surrounding environments, so they are active primarily during the warmer seasons, and like reptiles they generally become dormant during the cold winter months. Because Alabama's climate is so moderate, however, some amphibians may remain active during much of the year; one may hear some frogs singing even in January and February. Most amphibians that occur in Alabama are also native to other southeastern states.
Amphibian skins contain mucous glands that make them moist, cool, and usually slippery to the touch. Because they are small and generally docile creatures, amphibians are considered harmless to humans, but many species (such as toads and newts) have prominent poison glands, typically described as "warts," in their skins that make them unpalatable to many potential predators. However, some animals, such as the hognose snake (which feeds almost exclusively on toads), appear to be unaffected by the skin toxin. A dog or cat that bites a toad may experience discomfort, nausea, and foaming at the mouth.
Alabama is home to approximately 70 species of amphibians: 40 species of salamanders and 30 species of frogs and toads. Alabama amphibians are divided into the tailed Order Urodela (or Caudata), which includes the salamanders, and the tail-less Order Anura, which includes the frogs and toads. A third group of amphibians (Order Gymnophiona) consists of tropical, limbless, wormlike, burrowing amphibians known as caecilians. However, none of these species occurs within Alabama.
Types of Alabama Amphibians
Salamanders (Order Urodela or Caudata). Alabama has 40 species of aquatic or terrestrial salamanders and one species of newt, the Eastern Newt (Notophthalmus viridescens). Newts are members of the family Salamandridae that are aquatic during most of their adult lives and, unlike most salamanders which have smooth skins, have a grainy skin that produces toxins. There is only one species of newt which occurs throughout Alabama. Both the larvae and adults of salamanders are carnivorous and possess tails and generally the two forelimbs. Some aquatic salamanders have tiny or vestigial hind limbs or none at all. Unlike frogs and toads, among which males fertilize eggs as the females lay them, male salamanders deposit sperm in gelatinous packets called "spermatophores." These packets are picked up by the female's cloaca to fertilize her eggs internally. Aquatic salamanders lay their eggs in water, where the larvae develop and live for a period of weeks or months. The opportunistic larvae eat animals that are small enough to swallow, including worms, crayfishes, and insect larvae. Some terrestrial salamanders lay their eggs in humid environments such as rotting logs, where the larvae complete their development within the egg before hatching.
The Plethodontidae is the largest family of salamanders, and it includes lungless species that breathe exclusively through the skin. Although many species have aquatic larvae and are terrestrial as adults, some species are completely terrestrial and others are permanently aquatic. The major categories of salamanders include the slender woodland salamanders, burrowing "mole" salamanders, robust and aquatic hellbenders, newts, and aquatic, eel-like sirens and amphiumas. Because of their small sizes and docile natures, most salamanders are considered quite harmless to humans. They do have small teeth, however, and larger aquatic species, such as the amphiuma, can inflict a painful bite.
Permanently aquatic species, such as amphiumas and sirens, exhibit "neoteny," whereby individuals retain larval features such as gills throughout their lives, and a few even reproduce in the larval form. Alabama has salamanders that live in ponds, streams, seeps, woodlands, and caves. Depending on size and where they live, they may consume a variety of insects, worms, crayfishes, and fishes. Some species, including hellbenders, green salamanders, mudpuppies, and cave salamanders, occur only in the northern regions of the state. Flatwoods salamanders, dwarf salamanders, amphiumas, and some sirens live only in the southern parts of Alabama.
Alabama's smallest salamander, at only 2.9 inches in length, is the four-toed salamander (Hemidactylium scutatum), which ranges throughout the eastern United States and lives in moist woodlands and floodplains. The largest salamander species in North America is the eastern hellbender (Cryptobranchus alleganiensis), which extends throughout the Apalachian mountains. It may attain a maximum length of nearly 30 inches and lives in mountain streams of northern Alabama. The federally threatened Red Hills salamander (Phaeognathus hubrichti) is the only amphibian that is endemic to Alabama, meaning that it occurs here and nowhere else. Found only in ravines of hardwood forests in the Red Hills district of south-central Alabama, it is the official state amphibian.
Frogs and Toads (Order Anura). Alabama is home to 30 species of frogs and toads, all of which produce tailed, herbivorous larvae that become tailless, carnivorous adults. Adult anurans exhibit elongated hindlimbs that evolved for jumping or hopping. Anurans include the true frogs, tree frogs, and the more terrestrial toads. Anurans are the most diverse, successful, and widespread of all amphibians; none in Alabama have permanently aquatic adults. Except for the completely terrestrial, introduced greenhouse frog (Eleutherodactylus planirostris), all other anurans in Alabama have free-living, aquatic tadpoles. The greenhouse frog has a scattered distribution along the Gulf Coast from Florida to Louisiana; in Alabama it is usually found only in southern Mobile and Baldwin counties, although it appears to be expanding its range. This frog is unusual in that its young pass through the larval stage within the egg and hatch into 1/4-inch-long froglets with a small vestigial tail. Anurans are the only amphibians to produce vocalizations or possess external ears by which to hear them. The distinctive calls, which are produced only by males, can be readily identified by attentive listeners.
Except for the bullfrog (Rana catesbeiana), adult female anurans are typically larger than males of the same species. All anurans in Alabama engage in external fertilization, whereby the male fertilizes eggs in the aquatic environment. During the breeding season, males migrate to breeding sites (often ditches, ponds, or lakes) to establish "breeding choruses." These groups of males produce distinctive calls unique to the species that attract females to the breeding sites. Males clasp the females from behind in a process known as amplexus and fertilize the eggs as the female releases them. Some anurans attach their eggs to vegetation, and others deposit them singularly, in strings of large or small clusters. Egg clutches range from a few to a few thousand. Unlike salamanders, eggs of most frogs hatch into aquatic, tailed, herbivorous larvae known as tadpoles. (Salamander larvae, which look more similar to the adults, are regarded simply as larvae.) Anuran larvae may remain in their aquatic habitat for weeks, months, or even a few years, depending upon the species.
Commonly encountered near water, true frogs (family Ranidae) are familiar anurans that generally have smooth, moist skin and long hind legs that are well-adapted for jumping great distances. Unlike tree frogs and toads, true frogs are not specifically adapted for climbing or living on land. True frogs also have some distinctive skeletal adaptations. The two most common species of true frogs in Alabama are the southern leopard frog (Rana utricularia), which generally lives in marshes and the bronze frog (Rana clamitans), which usually inhabits aquatic, wooded habitats. Native to eastern and central Alabama and other northeastern and central states, the smallest true frog in Alabama is the wood frog (Rana sylvatica), having a body length of 2 inches. The state's largest frog is the bullfrog, which can reach a body length of 7.9 inches, not including the hind limbs. It has a call that may be described as a loud, low-pitched, conspicuous drone and is the species whose legs are commonly served in restaurants as "frog legs," although the legs of all true frogs are edible if skinned. Leopard frogs, bronze frogs, and bullfrogs occur throughout Alabama and are found in other states of the eastern and central United States.
The tree frogs (family Hylidae) have adhesive pads on the tips of their toes that they use to climb and cling to vegetation (trees or buildings). Although anurans are primarily insectivorous, the arboreal treefrogs eat more flying insects than do the true frogs or toads. The smallest member of the treefrog family, the little grass frog (Pseudacris ocularis), is found only in Alabama's southeastern corner. It has a maximum length of less than 3/4 inch, and the male produces a faint, high-pitched, tinkling call. The northern cricket frog (Acris crepitans) and the spring peeper (Pseudacris crucifer) are two small (typically less than 2 inches in body length), ubiquitous members of the treefrog family that are commonly found in wetlands throughout Alabama and most of the southeastern United States. The gray treefrog (Hyla chrysoscelis) and barking treefrog (Hyla gratiosa) are common treefrogs that occur throughout our state. Having a maximum body length of slightly less than 3 inches, the barking treefrog is Alabama's largest tree frog; the male has a call that sounds somewhat like a barking dog.
Ranging in body lengths from 1 to 3 inches, toads are the most terrestrial group of anurans; they have little or no webbing in the hind toes. Compared to true frogs and tree frogs, toads have stouter bodies, shorter legs, less webbing in the toes, and drier skins covered with prominent poison glands. The adults deposit their eggs in strings in water where the tadpoles complete their embryonic development. Unlike most true frogs and tree frogs, after the toad tadpoles metamorphose into toadlets, they leave the water for drier habitats in woodlands, countryside, or gardens. Toads cannot climb and do not frequent water, so they feed upon terrestrial animals such as insects, spiders, and worms. The largest toad in Alabama is the American toad (Bufo americanus), which is found in the northern part of the state; it reaches a length of 3 inches, and its call is a high-pitched trill. Ranging throughout the southern half of Alabama and having a body length of about 1 inch, the oak toad (Bufo quercicus) is Alabama's smallest toad; it has a call reminiscent of a baby chick. Ranging throughout Alabama and most eastern states, toads are the anuran group that people see most frequently and most often appear in gardens. Although not generally harmful to humans, the poison glands of toads make them distasteful to most predators. Alabama's most common and widespread species, Fowler's toad (Bufo fowleri), ranges throughout the state.
All plants and animals, including humans, and their environments are interdependent. Scientists do not yet understand the complex interrelationships of most amphibians, or indeed most other animals. However, we do know that amphibians play very important roles in the complex food webs of nature. Amphibians consume large numbers of invertebrates, including insects, and in the process remove and recycle vast amounts of nutrients, energy, and biomass. Some frogs lay thousands of eggs each year that provide food for animals in many aquatic ecosystems. Amphibian larvae and adults are consumed by fishes, reptiles, mammals, birds, and other amphibians. Because most amphibians are shy, secretive animals, however, most people do not have much appreciation for them. It is critical, however, that amphibians and the fragile habitats in which they live are protected.
Amphibians constitute valuable bio-indicators of environmental integrity. Most do not survive well in greatly disturbed habitats. Amphibian populations are on the decline all over the world, especially in the tropics, and also in Alabama. Some factors responsible for the decline of amphibians in Alabama and elsewhere include habitat destruction, environmental contamination from pesticides and pollution, invasive exotic species, diseases such as fungal chytridiomycosis, and overcollection for food or the pet trade. Although a number of Alabama amphibians are protected by state laws, the only federally endangered amphibians are the dusky gopher frog and the flatwoods salamander. Both of these animals have suffered from severe habitat destruction. Alabama's official state amphibian, the federally threatened Red Hills salamander, is being studied extensively. Some of its habitats are being carefully managed and protected. Long-term studies will require many years to determine whether or not the population is stable.
Some people choose to keep amphibians as pets. But they are shy animals with specialized habitat and dietary requirements and thus generally do not make good pets. Few people are willing to learn how to care for them properly. It is best to observe and enjoy amphibians (and all wildlife) in their natural habitats and leave them where they are likely to survive. Animals collected and kept in artificial, inappropriate settings usually die. Each year, many tadpoles die unnecessarily when people collect and keep them in conditions where they cannot survive. Exotic species available in pet stores should never be released into the wild under any circumstances. Diseases from captives may spread and devastate native populations that have no natural defenses against introduced diseases. Specimens are inadvertently introduced within potted plants that are imported from warmer climates.
Alabama enjoys one of the greatest amphibian biodiversities within the United States. However, Alabamians need to become better
stewards of their natural resources and take steps to ensure that they and their habitats are treated with care and respect.
Amphibians should be viewed as valuable members of the state's unique and diverse natural environment.
Dorcas, Mike, and Whit Gibbons. Frogs and Toads of the Southeast. Athens, Ga.: University of Georgia Press, 2008.
Mirarchi, R. E., M. A. Bailey, T. M. Haggerty, and T. L. Best. Alabama Wildlife. Volume 3: Imperiled Amphibians, Reptiles, Birds, and Mammals. Tuscaloosa: University of Alabama Press, 2004.
Mount, Robert H. Reptiles and Amphibians of Alabama. Tuscaloosa: University of Alabama Press, 1975.
Petranka, James W. Salamanders of the United States and Canada. Washington, D.C.: Smithsonian Institution Press, 1998.
David H. Nelson
University of South Alabama
Published August 10, 2010
Last updated June 27, 2013