Amphibians

The word "amphibian" is derived from the Greek words "amphi" and "bios" which means two lives and refers to the aquatic tadpole and the terrestrial adult stages of all salamanders, newts, frogs, and toads. In a process called metamorphosis, which usually occurs over the course of a few weeks, the larval tadpole transforms into its adult frog and toad like form with which we are familiar.

Amphibian life cycle.	Amphibians absorb water through their skin.

In southern Ontario the first frogs begin to call the last week of March. In central Ontario frogs call the first week of April and in northern Ontario frog calls can be expected in late April. Calls and breeding periods may last several weeks for some species or just a few days for others. Consult "Familiar Amphibians and Reptiles of Ontario" for further information.

Amphibians hatch from eggs laid in the water and pass through a distinctive tadpole/larval stage (a month for toads and up to three years for bullfrogs). The larvae of most species are aquatic and possess gills and prominent fins. Frog and toad tadpoles graze on algae and small organisms in the water; larval salamanders and newts are carnivorous and feed on aquatic insects. During metamorphosis, they acquire legs and lungs. Significant changes in the digestive system coincide with

changes in feeding behaviour. Adult amphibians may live on land, but must return to water to breed and, in some cases, to hibernate. One species of salamander in Ontario differs from this typical pattern. The redback salamander lays its eggs out of the water. The female seeks a moist, rotting log within which to lay her eggs. Fully formed little salamanders hatch from the eggs!

During the cool winter months Ontario amphibians: 1 ­avoid frost by burrowing below the frost line (common toad), 2­avoid frost by hibernating underwater in rivers, lakes, and ponds (leopard frog). 3­hibernate in forest leaf-litter where frost is resisted by developing a sugary antifreeze and tolerating ice in their body (wood frog). Mammals and birds use energy in food to keep their bodies warm while amphibians and reptiles absorb heat directly from their environment. As a result, amphibians do not have to eat as often or as much as birds and mammals, and they do not eat at all during the six months of winter hibernation.

The male toad calls to attract females to the breeding pond.

Amphibians do not drink. They absorb water and much of the oxygen they need through the skin, although they use their lungs as well. Some species are active at night and avoid the drying effects of the sun. Others shelter in moist habitats under logs, rocks, leaves or mosses and ferns. Amphibians shed their skin about once a week. Most frogs and toads eat their skin which splits down the back and which they then pull into the mouth with their front legs. We must not look at these animals as if they were less advanced. Amphibians are superbly adapted to their environments.

The biomass of woodland salamanders may be greater than that of birds and small mammals.