Providing a soundtrack for summer nights isn’t the only kind of croaking some of the world’s frogs have been doing lately. Vanishing Amphibians Task Force Head Dr. Ron Meyer and other scientists around the globe are investigating mysterious declines in frog populations, some in seemingly pristine environmental niches. They fear the frogs’ demise may portend greater environmental catastrophe brought on by a synergy of civilization-derived sources such as ozone depletion. If they’re not successful, we’ll have to rely on sources such as the just re-issued Folkways classic of naturalism Sounds of North American Frogs, recorded between ’54 and ’57 by pioneering herpetologist Charles M. Bogert, for evidence of the amphibians’ still-substantial but threatened biodiversity. Meyer and local filmmaker Allison Argo will introduce her documentary on the search for the frogs’ killer, The Last Frog, at noon at the Museum of Natural History’s Baird Auditorium, 10th & Constitution Ave. NW. Free. (202) 357-2700. (Daniel Searing)