Fruiting, fruit feeding, and seed dispersal by birds at four isolated tree species in Kodaira, western Tokyo

Abstract

Seed dispersal by birds is important for conserving biodiversity in urban green space. Isolated trees in urban environ-ments with paved ground surfaces are suitable for collecting seeds, which is difficult in complex forests. The timing of fruiting of four tree species (Melia azedarach, Toxicodendron succedaneum, Ligustrum lucidum, and Ilex rotunda), their use by birds, seed delivery, and the relationships among the sizes of the fruit, seeds and bird bills were studied in Kodaira in western Tokyo, Japan, from December 2020 to March 2021. The timing of fruiting and seedfall synchronised in L. lucidum and T. succedaneum, while seedfall was delayed by 2 weeks in M. azedarach and 1 month in I. rotunda. Birds delivered seeds of 11-29 plants to the focal trees. The numbers of seeds recovered under the target trees ranged from 900 to 1300 seeds/m², except for M. azedarach (-30 seeds/m²). The proportion of seeds delivered from elsewhere was 47.7% in M. azedarach and less than 20% for the other three species. The majority of fruits were smaller than 10 mm in diameter, which was smaller than the bill width of the brown-eared bulbul (Hypsipetes amaurotis, 15.4 mm), except for those of Trichosanthes cucumeroides and Neoachmandra japonica.