When did scientists first notice the changes in local amphibian populations?

In the 1980’s scientists began noticing startling declines in amphibian populations. An alarming number of individual frogs and salamanders were also identified with unusual deformations and mutations. Scientists have determined that 32% of global amphibian species are threatened. This is due to numerous reasons including water and air pollution and habitat loss. Amphibians appear to be especially sensitive to pollution because they have shell-less eggs, they have permeable skin and they spend part of their life in water. For this reason, they are considered to be an indicator species. An indicator species is a plant or animal whose absence or presence in an ecosystem can suggest certain conditions. Therefore, declines in amphibian populations may indicate that there are significant changes occurring in our water bodies.    
There are 22 species of salamanders and 16 species of frogs and toads in Pennsylvania. Delaware is home to 14 species of frogs and toads and 13 species of salamanders.  Learn more at the Pennsylvania Herpetological Atlas.