DISAPPEARANCE OF THE CASCADES FROG RANA-CASCADAE AT THE SOUTHERN END OF ITS RANGE, CALIFORNIA, USA

It has recently become evident that amphibian species in many areas of the world have suffered serious declines. Healthy, seemingly well-protected populations have disappeared for no obvious reason. Data from historic accounts and museum records indicate that the Cascades frog, Rana cascadae, was once abundant at the southern end of its range in the vicinity of Lassen Volcanic National Park, California, USA. We conducted intensive searches at all 16 sites where R. cascadae had previously been recorded in the Lassen area, plus 34 additional sites with suitable habitat. Whereas earlier biologists could sometimes find 40 or more frogs at some of these sites, we were only able to locate two frogs at a single locality. This represents a precipitous decline over a period of <15 years. The decline seems to have been caused by a combination of local factors, including (1) the presence of non-native, predatory fish which have restricted habitat and limited dispersal of frogs; (2) loss of breeding habitat due to a five-year drought; and (3) the gradual loss of open meadows and associated aquatic habitats. The loss of frogs suggests that some common management practices in parks and wilderness areas may be endangering some of the species these areas are intended to protect. Similar local factors may account for amphibian declines reported elsewhere and should be carefully evaluated along with possible global effects.