Ecology: Global amphibian population declines

The decline and disappearance of relatively undisturbed populations of amphibians in several high-altitude regions since the 1970s suggests that they may have suffered a global decline, perhaps with a common cause or causes. Houlahan et al. examined means of trends for 936 amphibian populations and concluded that global declines began in the late 1950s, peaked in the 1960s, and have continued at a reduced rate since. Here we re-analyse their data using a method that accounts for the sampling of different populations over different time periods, and find evidence of a mean global decline in monitored populations only in the 1990s. However it is calculated, the global mean not only masks substantial spatial and temporal variation in population trends and sampling effort, but also fails to distinguish between a global decline with global causes and the cumulative effects of local declines with local causes.