Seasonal Fluctuation of Soybean Damage Intensity by Rufous Turtle Dove Streptopelia orientalis and the Factors Affecting It

Abstract

In order to investigate the seasonal fluctuation of damage intensity by doves, we sowed upland field of National Agriculture Research Center, Ibaraki Pref., with soybeans every other week and counted the number of soybeans damaged between April and August, from 1981 through 1986. Rufous Turtle Doves Streptopelia orientalis, the main predators on soybeans, were free to eat soybean seeds and/or cotyledons.1) The percentage of seeds eaten before germination was low in April, high in May, and became low from June again. The percentage of seeds eaten in the first sowing of the year was always lower than the second sowing, probably due to that the doves are unaccustomed to the cropping field at the time of the first sowing.2) The damage after germination (soybeans pulled out, growing point eaten, one or two coty-ledons eaten) was also intense in May but the degree of damage dropped in June. The percent-age of damage fatal to the plant (i.e. soybean pulled out and growing point eaten) was high when the percentage of total damage after germination was high.3) The percentage of the number of soybeans (both seeds and cotyledons) damaged was high before the ripening of barley and became low just after the ripening.4) The relationships between the seasonal fluctuation of soybean damage and the maturity stage of barley in other areas of Japan, the seasonal changes in the food habits of feral pigeons shot in the neighborhood of study area in spring, the change in behavior of Rufous Turtle Doves during the harvest period of wheat and barley, and the amount of barley and wheat that dropped on cropland at harvest were discussed. We suggested that a decrease in damage inten-sity of soybeans in June strongly related to the maturity stage of barley.