National Geographic: Silent and secretive creatures, salamanders are just as quietly falling off the map in tropical forests throughout Central America, a new study says. Two common species surveyed in the 1970s in cloud forests of southern Mexico and Guatemala are extinct, and several others have plummeted in number, researchers say. The tiny amphibians seem to be on the same downward spiral as their frog cousins, which have been mysteriously declining for years. Scientists have identified …