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1.  What you can do
2.  Water
3.  Ecology
4.  Amphibians
5.  Environmental Issues
6.  Keystone species
7.  Get Wet!-
     Field Study Ideas

8.  The Zoo Experience
9.  Frogs & Friends
10. Case Studies
11. Resources
12. Glossary

Wetland Curriculum Resource
Unit 4. Amphibians - Background for Educators

Ontario is inhabited by a great diversity of wild life species. Amphibians are among the least known of the vertebrate animals. This lack of understanding may be the leading cause for the decline of our amphibian populations in Ontario.


It is believed that amphibians evolved from the Class Osteichthyes (the fishes) some 300 million years ago. Amphibians were the first vertebrates to spend part of their lives out of water. The word amphibian means "double life". This refers to the two stages in their life cycle. During the first stage they live in water as gilled, larval forms, and during the second stage, they live on land as lung-breathing adults. But this generalization is not true for all amphibians. Some, like the mudpuppy, never leave the water. It remains, and breeds in a larval state without undergoing metamorphosis. While still others, like our Eastern Red-back Salamander, do not breed or lay eggs in water. Eggs are laid in rotting logs and fully formed (but tiny!) salamanders emerge from the egg.

As evolution occurred, lack of competition from other species enabled amphibians to populate and expand their distribution. However, amphibians remained dependent on water to reproduce. Millions of years later, an Order of amphibians known as Anthracosauria gave rise to one the most successful groups of animals on the earth today: the reptiles.


Amphibians are classified into three distinct Orders, based on physical structure. All tailed amphibians belong to the Order Caudata, which includes the salamanders and newts . All tailless amphibians belong to the Order Salientia (formerly Anura) which includes the frogs and toads. All legless, worm-shaped amphibians are called caecilians, and belong to the Order Apoda. In Ontario, 23 species of amphibians exist, 10 tailed amphibians, and 13 toads and frogs. If you wish to pursue activities related to classification see Exercise 4.8, Classing Creatures and in Unit 8, The Zoo Experience, Tour 3: Who's Who - Classifying Animals.

Physical Structure

The following are characteristics which are common to all amphibians:

  • possess thin, moist, glandular skin (no scales)
  • eggs possess a soft outer membrane, are laid in water or moist environments, and are protected by a gelatinous coating
  • aquatic larvae breathe through gills
  • larvae undergo metamorphosis to adult form
  • possess a three-chambered heart with inefficient mixing of oxygenated and unoxygenated blood in a single ventricle

All amphibians are ectothermic, or cold-blooded. This means that their body temperature is determined by the surroundings. Hence, amphibians are able to control their body temperature by basking in the sun, or cooling it in the shade. Unlike warm-blooded animals, they do not rely on food energy to maintain body temperature but depend on heat (from the sun) for physical activity. As a result, amphibians do not have to eat as much food as similar-sized birds or mammals. While hibernating over the winter, they do not eat at all.

The amphibian's thin, moist skin is important for respiration and protection. The skin possesses two types of glands: mucous glands which keep the skin soft and moist, and granular glands which produce secretions used to ward off predators. The toxicity of the secretions varies between species, and some may be quite repulsive or even deadly to predators.

Amphibians do not drink water but, since their skin is very permeable, they can obtain water by osmosis. This is one reason why amphibians require a moist habitat. Frogs bask along the shorelines of lakes or marshes to replenish the water that is lost by the sun's heat. The skin of an amphibian is vital to its existence, and therefore must be kept in good condition. As a result, it is shed weekly. The skin splits down the back, and some species use the front legs to draw it into the mouth and it is eaten.

Because amphibians lack effective teeth and claws, they are generally defenceless. They rely on secretive behaviour to escape detection, and often cryptic colouration which enables them to blend in with their habitat. Some species have poisonous skin secretions. Salamanders can actually lose parts of their bodies to predators (better to lose a tail than a life). They can regenerate lost tails, toes or limbs. Frogs and toads are unable to do this.


Amphibians possess a diverse respiratory system. Gas exchange between the environment and the blood occurs three ways: through the skin (cutaneous respiration), through the lining of the mouth and pharynx (buccopharyngeal respiration), and through the lungs (pulmonary respiration). The amount of gas exchanged through these different surfaces varies between species; oxygen levels; activity; habitat use; and temperature. All respiratory membranes share three common characteristics: they have to be kept moist, they have to be thin (one cell thick), and they have to be well supplied with blood vessels.


Ontario is home to eight species of salamanders, and one newt. The following table lists the representative families and their species:






Red-spotted Newt

Ambystomidae (mole salamanders)

Spotted Salamander
Blue-spotted Salamander
Jefferson Salamander
Smallmouth Salamander

Plethodontidae (lungless salamanders)

Northern Dusky Salamander
Eastern Red-back Salamander
Four-toed Salamander
Northern Two-lined Salamander

General Characteristics of Salamanders and Newts

In general, salamanders are secretive, nocturnal animals. In locating them, one would have to search along small streams or moist woodlands. You would have greater success in seeing them on a spring night, especially after rain. This is when they are most active. However, during daylight hours, they find shelter under stones or damp, rotting logs. Unless you can return a log or stone to its original placement, it should not be moved when trying to locate them. Disrupting a salamander's habitat causes temperature increases, moisture loss, and loss of cover. It is not worth the risk of adding stress to the salamander's life.

During periods of excessive heat, salamanders enter a state of dormancy called aestivation. During this period, they move deep underground and select a cool site with a high level of humidity to avoid moisture loss in their bodies. As winter approaches, salamanders move underground through root systems and tunnels, or migrate to the bottom sediments of ponds or marshes. They enter a state of dormancy called brumation. Because salamanders cannot tolerate a frozen environment, they must tunnel below the frost line, or the water temperatures below the ice must remain above freezing.

Salamanders are extremely important in a forest ecosystem. They occupy a niche that would not otherwise be used. They feed extensively on insects, crickets, spiders, ants, grubs, and worms, and they accumulate stored energy to be passed on to other animals in the food chain. In some eastern forests, Red-back Salamander biomass exceeds that of small mammals or birds.


All North American salamanders lay eggs, as few as six and as many as 150. Breeding season usually occurs in late March or early April in marshes, weedy ponds, and temporary or permanent woodland pools. One species, the Eastern Red-back, lays eggs on land in wet logs, and fully formed salamanders are hatched. The Four-toed Salamander lays eggs in a moss nest along the edges of ponds. Male and female salamanders look alike except during the breeding season when the male has a swollen gland around the vent (behind the back legs). During breeding, salamanders display an elaborate tactile courtship. The male then deposits a package of sperm known as a spermatophore. A receptive female picks up the spermatophore which she stores in her cloaca. Fertilization is internal, and the fertilized eggs are deposited on submerged sticks, plants, or leaves. The eggs hatch into larvae with external gills which they maintain throughout their aquatic life. Unlike frog tadpoles, salamander larvae develop front limbs before their hind limbs. Salamander tadpoles have broad mouths with tiny teeth adapted for a carnivorous diet. They remain as larvae until metamorphosis occurs, after which they transform into a terrestrial adult.


The Mudpuppy is the largest tailed amphibian found in Ontario. It is totally aquatic and often caught by anglers, who are scared to death of their catch! They are the only Ontario amphibian that maintain gills throughout their whole life cycle.


The Red-spotted Newt is Ontario's only newt. A unique aspect of this amphibian's life cycle is that it occurs in three stages. It begins as an aquatic larvae, transforms to a poisonous terrestrial Red Eft stage, and then returns several years later to the water as a mature newt. Sometimes the terrestrial stage is omitted and the larvae transform directly into adults.


Mole salamanders are so named because they spend a lot of time underground or under leaf litter. Lungless salamanders do not have lungs but rely on cutaneous and buccopharyngeal respiration. There are two groups of lungless salamanders. These include a single species of dusky salamander and three species of woodland salamanders.

Salamanders are secretive and, unlike frogs and toads, they do not make their presence known through loud calls and songs.

On many occasions, lizards have been confused with salamanders. Although they are similar in appearance, lizards are reptiles that have scales on their body and claws on their toes. The only lizard in Ontario is the Five-lined Skink which has a limited distribution (found at Point Pelee and south of a line joining Parry Sound and Kingston), and is more commonly found in hot, drier habitats.


Ontario is home to 11 species of frogs and 2 toads. The following table lists the representative families their species:




American Toad
Fowler's Toad


Blanchard's Cricket Frog
Spring Peeper
Gray Treefrog
Boreal Chorus Frog
Midland Chorus Frog

Ranidae (true frogs)

Green Frog
Mink Frog
Wood Frog
Northern Leopard Frog
Pickerel Frog

General Characteristics of Frogs and Toads

In general, frogs and toads are look similar but they have a few differences:



smooth, moist skin

warty, dry skin

long legs

short legs



small waists

wide waists

no enlarged poison glands

enlarged poison glands (parotids) on neck

Frogs and toads can be found in a variety of moist habitats. Some species are totally aquatic, while others tend to be more terrestrial, spending their time on land. Either way, they still need wet or damp conditions to reduce or replenish body moisture loss. Frogs and toads consume large numbers of terrestrial and aquatic insects. They also provide a food source for a wide variety of woodland and aquatic predators. Most species of frogs and toads share the adaptation of cryptic colouration which allows them to blend in with their natural habitat. Toads possess glands which secrete toxins that are irritating to predators. Treefrogs (Blanchard's cricket frog excepted) possess adhesive discs on their toes which help them to climb and cling to branches, twigs, and bark (a lesser extent in chorus frogs). True frogs have long legs with webbed feet and are excellent leapers and swimmers.

Most frogs and toads are best observed at night with the aid of a flashlight, or by listening for calls. Frogs and toads were the first vertebrate animals to possess vocal chords. Although both sexes have vocal chords, they are better developed in males. Only the males have vocal sacs. When filled with air they resonate loud calls during the breeding season. Each species has its own distinctive call and time for breeding. Breeding season is by far the best time of the year to observe them.

The eardrum of frogs and toads is called a tympanum. It is a thin membrane found on both sides of the head, just behind and below the eye, and functions to receive airborne sound waves.

As winter approaches, frogs and toads seek out either terrestrial or aquatic sites to hibernate. Toads, wood frogs, spring peepers, chorus frogs, gray treefrogs, and rarely green frogs hibernate on land in the leaf litter or below the frost line. The pickerel, northern leopard, mink, green, and bullfrogs usually spend the winter under water, on or in the bottom sediments.


All North American frogs and toads lay eggs, as few as 19 and as many as 30,000. Breeding season for some species begins in late March or early April, and extends to June for other species, taking place in rivers, marshes, and temporary or permanent ponds. Males emit a distinctive call during the breeding season (females do not call), to proclaim their territories or attract females. When the female approaches a male that she chooses to breed with, they assume a position known as amplexus, where the male grasps the female from behind with his front legs and holds on tightly. The female releases the eggs into the water, sperm is released by the male, and external fertilization occurs. The eggs hatch into tadpoles two to 10 days later depending on the species and water temperature. As the larvae develops, in the egg the gelatinous layers surrounding it begin to disintegrate by secretions from the tadpole's snout. The tadpoles hatch with external gills which are lost within a few days. Unlike salamanders, frog and toad tadpoles possess small, round mouths and rasping teeth which are specialized for a herbivorous diet. The time required for total metamorphosis from larvae to adult varies in species, from 21 days for toads to 3 years for bullfrogs. The following changes occur in the metamorphosis process:

  • growth of a wide mouth and loss of horny jaws
  • loss of gills, closure of gill slits, and development of lungs
  • emergence of forelegs
  • reduction in length of the intestine (from herbivore to carnivore)
  • reabsorption of tail
  • emergence of back legs

Frog and Toad Calls

Detailed descriptions of the life history and habitats of Ontario's frogs and toads, as well as recordings of their calls, can be found in our Guide to the Reptiles and Amphibians of Ontario.


The issue of declining amphibian populations was considered at the first World Congress of Herpetology in 1989. Since then, there have been many documented accounts of decline or disappearance of amphibian species all over the world. Scientists have reported such declines in the United States, Australia, Costa Rica, and Canada. It has become such a concern in some countries, that tunnels have been built under roads to ensure toads and salamanders can cross safely to their breeding habitats.

The loss of amphibians from pristine habitats such as Costa Rica indicates that there may be other factors affecting populations. Global issues that have concerned scientists are global warming, the increase in ultraviolet light striking the earth, and acid deposition. Water is vital in the life cycle of an amphibian. Toxins in the water easily pass through the amphibian's sensitive skin, causing serious and painful injury or death. Some species are less resilient and quickly succumb to the effects of the toxins. Any contaminant that changes the air, water, or plant and animal food has a direct effect on amphibians. Because amphibians are so sensitive to these changes, their disappearance could be a warning to us. With this advanced notice, we can all act to restore or improve the quality of the environment around us.

A Local Issue - A Need For Concern

Southern Ontario has lost nearly 70% of the wetlands that amphibians rely on for breeding. This loss of habitat has an immediate impact on amphibian populations. Another related impact is the effects of drought. During years of drought, wetland areas become dry, leaving no place to breed, or they dry up before the tadpoles have had sufficient time to develop. Droughts occur in cycles, and under normal circumstances, we can expect to have good and bad years. However, with the loss of so many wetlands, amphibians have lost the linkages that allow them to move from wetland to wetland. Isolated populations disappear and often cannot be re-populated.

NOTE: These issues of global and local amphibian decline are discussed in the four case studies contained in Unit 10: Case Studies.

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