Frogwatch is a volunteer frog monitoring program where people watch for and report frog activity. Their site has a plethora of information on how and why to do so, including this scary stuff:
"Around the world amphibians are declining. This is occurring in pristine wilderness areas as well as severely modified suburban wetlands. It is unlikely that there is only one global cause of this decline, rather amphibians are being affected by a variety of causes, including increased UV radiation and chemical pollutants. Some species, such as the Golden Toad of Costa Rica and possibly as many as seven species from Australia are now extinct. The loss of the Golden Toad is particularly sobering as it became extinct despite the fact that its habitat was protected in a large nature reserve.
No Canadian species have become extinct, but the Northern Cricket Frog, which was limited to extreme southwestern Ontario, has not been seen in Canada in over a decade. The disappearance of species at the edge of their ranges is troubling, but even more disturbing is the collapse of a species across much of its range. The Northern Leopard Frog was once one of the most common frogs in western Canada, yet in the late 1970s it vanished from much of its range. Dead frogs were found in some areas in Manitoba, but in other provinces the disappearance went virtually unnoticed. Today, the Northern Leopard Frog is considered endangered in both British Columbia and Alberta.Possibly even more threatening than the introduction of exotic animals is the spread of foreign microorganisms. Scientists have recently discovered one or more fungi that are responsible for mass die-offs of frogs in both the rainforests of Panama and Australia. It appears that the fungi that caused the die-offs were not native to these sites but have been introduced. For some reason the fungi became infectious parasites that ultimately killed their hosts. It remains unclear whether the frog populations were healthy before the fungal infection, or whether there is another factor to explain the frogs' susceptibility to the infection."