Frogs, toads, and some salamanders go through an aquatic (water-dwelling) “larval” stage with gills, and then metamorphose (transform) into an adult form that lives on land and breathes air. You have probably seen the transformation of tadpoles into frogs. Aquatic-breeding amphibians lay their eggs in spring amongst vegetation in shallow areas of wetlands, lakes, ponds, and slow-moving streams. A few of our native species, such as the tailed frogs and Coastal Giant Salamander, breed in fast-flowing mountain streams. For most of these species, their young develop and change into a terrestrial form within the same year, often in late summer. The majority of B.C.’s native aquatic-breeding amphibian adults and newly transformed young spend most of their life on land in areas around wetlands and streams, or in upland forest areas. We know little about how far amphibians travel from breeding sites, but some studies suggest that they move hundreds of metres, and sometimes even a few kilometres into upland areas.
Not all salamanders leave the water. Some aquatic-breeding salamanders reach sexual maturity (become adults) in their larval form, retaining their gills and spending their entire lives in the water. To make the story even more interesting, some salamanders like the Western Redback Salamander, never enter a pond at any stage in their lives. These salamanders, called terrestrial salamanders, lay their eggs on land under logs and rocks. Their young hatch looking like miniature versions of their parents (i.e., they do not transform). Unlike their aquatic-breeding counterparts, individuals of these terrestrial salamander species may move relatively little, potentially spending their entire life in one large log on the forest floor.
Most amphibians have smooth, moist skin that is very permeable to liquids and gases. Adult frogs absorb part of the oxygen and most of the water they need through their skin. Some salamanders, like the Western Redback Salamander, get all their oxygen this way since they have no lungs. In addition to permeable skin, amphibians are also ectotherms (i.e., ‘cold-blooded’). This means that amphibians cannot generate their own body heat like we can and they move to micro-habitats in their environment daily and annually to maintain a suitable body temperature for digestion and growth. All amphibians in temperate environments become dormant during winter. The majority of our amphibians seek cover underground or underwater away from freezing temperatures. A few species, like the Wood Frog, have a unique physiology which can withstand freezing solid in winter.
Due to the permeable nature of their skin, amphibians must live in moist environments or avoid being active during periods of extreme climatic conditions. An exception to this are the grassland amphibians of the southern interior, such as the Great Basin Spadefoot, which have evolved specialized behaviours to help them cope with periods of extremely dry and hot conditions. While the permeable nature of their skin helps amphibians in some ways, it also makes them vulnerable to pollutants and conditions that cause them to dry out or heat up (e.g., loss of forest cover). Their dependency on two habitats (uplands and in water), the need to move between these areas to meet all of their life history requirements, and the permeable nature of their skin, exposes amphibians to a wide array of environmental issues.