Population Change of Jungle Crows in Tokyo

Abstract

　We conducted a literature survey on changes in population and distribution of jungle crows (Corvus macrorhynchos) in Tokyo and analyzed possible factors affecting the changes. The number of crows in five major roosts in central Tokyo drastically increased in the mid-1980s through the mid-1990s, leveling off and/or slightly decreasing afterwards. In 2001 and 2002, 33 crow roost sites were observed in Tokyo. Although the histories of these minor roosts are poorly known, some of them were established, or increased in roosting numbers, in the 1990s. Therefore, the increase in crow population in Tokyo has not stopped but entered a different phase.

　The period during which the crows started to increase was synchronous with that when domestic garbage began to be disposed in plastic bags for pickup, but not when the amount of food scraps in the garbage reached its peak. Considering that buckets with tight lids prevent crows from scavenging the food scraps inside the container, but that flimsy plastic bags allow crows easy access to the food scraps, these results suggests that the population of crows in Tokyo was more affected by the change in availability of food scraps than their quantity.

　The distribution of breeding jungle crows increased at urban sites in the 1990s and decreased in woodlands compared to the 1970s. Jungle crows came to breed in areas with less vegetation cover and higher urbanization rates, which led to the increase in distribution.