There does not appear to be one 'smoking gun'; numerous environmental factors are probably responsible for the declines and deformities.
Multiple limbs, missing limbs, and facial abnormalities are the main developmental malformations seen.
In response to indications of worldwide declines in amphibian populations, the President and Congress directed Interior Department agencies to initiate a national program of amphibian monitoring, research, and conservation.
Learn more:Amphibian Research and Monitoring Initiative