The decline in population size of the Tree Sparrow Passer montanus in Japan

Abstract

It is commonly thought that Tree Sparrow Passer montanus numbers have decreased in Japan in recent decades. Here, in order to ascertain this surmise, the population decline in the last several decades was estimated based on published articles and data. The analysis shows that the overall population has fallen by at least half since 1990 and by more than 90% since the 1960s. These results indicate the necessity of monitoring and managing this once abundant species in Japan.