California Red-legged Frog
California red-legged frogs were nearly wiped out due to demand for their legs—a specialty in some restaurants. Today they face a different threat: pesticides. Frogs' thin skin is sensitive to pollution. As air and water pass through it, so do harmful chemicals. So health problems in frogs can be an early warning for environmental problems. The first to discover pollution-related sickness in frogs were middle-school kids in Minnesota.
 

Northern Spring Peepers
Spring peepers can be heard in some northern states long before the snow has melted. The high-pitched peeps of these tree frogs are one of the first signs of spring. The earliest peepers appear with the first warm rain. As the ground thaws, more of them come above ground and join the chorus. Spring peepers can be found on trees, on shrubs, and in tall grass in wetland areas. A male peeper's call can be heard for more than half a mile! 
 

Arrow Poison Frog
Arrow poison frogs are less than two inches long—but they're the most poisonous animals on Earth. They carry their poison under their skin. The frogs' brightly colored skin warns other animals to stay away. Both male and female arrow poison frogs raise their young. Mom lays the eggs. Then dad carries them on his back until the tadpoles are ready to hatch. The parents raise their tadpoles in water that collects on tree branches and leaves.