It has been well known that tree sparrows Passer montanus ingest the nectar of cherry blossoms Prunus sp. without carrying pollen. This nectar-robbing behavior often causes cherry blossoms to drop prior to pollination. Since cherry blossoms are cherished in Japanese culture, some people are bothered by the nectar-robbing of sparrows. Here, we proposed a method by which to estimate how many blossoms were damaged by tree sparrows. In this method, we examined blossoms which had dropped on the ground under the trees, judged whether they were damaged by tree sparrows, and calculated the proportion that were damaged tree sparrows in relation to the total number of blossoms which had dropped. Applying this method to four study sites in Iwate Prefecture, northern Japan, we found that the number of the nectar-robbed flowers was very small (on the order of a dozen flowers / tree).
2010 by Japan Bird Research Association