How many Tree Sparrows Passer montanus are there in Japan?

Abstract

Tree Sparrows Passer montanus are one of the most common garden birds in Japan. The species' biology, however, is not well known. I have estimated the population size of this species in Japan, using a method of extrapolation based the results of field surveys and land-use data. The areas treated in this study include the five main islands of Japan: Hokkaido, Honshu, Shikoku, Kyushu and the Okinawa Island. The densities of Tree Sparrows' nests in five habitat types (central urban, residential, rural, other possible breeding, and non-breeding areas) were measured by counting the nests within survey plots during the breeding season in 2008. Each of the total area for the five habitat types in Japan was calculated from three different definitions of that habitat type (Table 1) which were applied to a database of Japanese land-use. The sum of the products of the density and the area for each of the five habitat types gave an estimated total number of Tree Sparrows' nests in Japan and its value was about 9,000,000. Assuming monogamy (i.e. two adults per nest), the number of adult Tree Sparrows at the breeding season in 2008 was estimated at about 18,000,000. Considering the roughness of the estimation method, the true population size was expected to lie in the range of two or three (or, one-half or one-third) times the estimated value.