Over the past 50 years scientists have recorded major declines in frog populations around the world. A few species have vanished completely. Many frog die-offs are the result of local human activity, but the epidemic has also reached remote areas. Is there a global cause? Scientists continue to search for answers.

American toad with throat pouch inflated

Bufo americanus

© James Harding, MSU

Major causes of frog declines:

• Habitat destruction
• Introduced species
• Chemical pollution
• Climate changes
• Over-collection
• Epidemic diseases

Frogs with extra or missing legs, eyes, and toes have been found in 44 states since 1996. Possible causes include parasites, pollution, and ultraviolet radiation.

In a laboratory study in 1997, nearly half of the frog eggs exposed to ultraviolet light grew into malformed adults, while eggs with no exposure developed into normal adults.