Frogs, Toads, and Their Kin

There are more than 4,000 species of amphibians in three main groups: frogs and toads (3,500 species), salamanders and newts (350 species), and caecilians (see SIL ee uns) (160 species). Frogs and toads have short tailless bodies with long hind legs. They range in length from 1 centimeter (0.4 inch) to 35 centimeters (14 inches). Toads differ from frogs in having rougher skin and spending most of their life on land. Most frogs and toads lay their eggs in water. Tadpoles (the aquatic stage of frogs and toads) develop from these eggs and live in the water until growing legs and becoming land-based adults. Many frogs, however, continue to spend much of their time in or around water.

Salamanders and newts have long bodies with tails. They range in length from 3 centimeters (1.2 inches) to 160 centimeters (63 inches). Although most salamanders and newts have two pairs of limbs, some aquatic forms have no hind limbs and only small forelimbs. Caecilians are limbless, wormlike amphibians found throughout the tropics. They range in length from 7 centimeters (2.8 inches) to 150 centimeters (59 inches). Some species lay eggs, while others give birth to their offspring.

The scientific community first began to learn about amphibian population declines at the First World Congress of Herpetology [the study of reptiles and amphibians], held in Canterbury, England, in 1989. David Wake, director of the Museum of Vertebrate Zoology at the University of California at Berkeley, presented evidence of dwindling frog populations in central and northern California. In 1990, an international group of about 40 biologists gathered in Irvine, California, to discuss research findings. As the scientists exchanged information, it became apparent to them that amphibian disappearances were a global phenomenon. The most disturbing development was that amphibians seemed to be disappearing not only from areas known to be disturbed by human activity but also from areas thought to be pristine wilderness.

In 1991, the Species Survival Commission, a division of the World Conservation Union (an international organization made up of more than 500 environmental groups), established the Declining Amphibian Populations Task Force (DAPTF). The DAPTF, based at the Open University in Milton Keynes, England, recruited more than 1,200 scientists, including me. Our research goals were to determine: (1) if amphibian numbers are, in fact, declining; (2) if so, why; and (3) what can be done to halt these losses?