Frugivory and seed dispersal by brown-eared bulbul of an evergreen shrub Aucuba japonica var. borealis in a Japanese cedar plantation, central Japan

Abstract

We investigated fruit removal from an evergreen shrub Aucuba japonica var. borealis to identify the seed dispersers in a Japanese cedar plantation, central Japan. In April 2015, we established four study plots in a cedar plantation of Ishikawa Agriculture and Forestry Research Center, Forestry Experiment Station, and every week we monitored the fate of 980 fruits of 51 fruiting individuals of Aucuba japonica var. borealis. We conducted camera-trapping to observe fruit removal by frugivores, and observed that 428 fruits (353 fruits on the trees and 75 fallen fruits on the forest floor) were removed from April to June 2015. Fruits were rapidly removed from the shrubs (41.7% of 980 fruits were removed after one week, 97.2% after two weeks, and 98.3% after three weeks). During 465 camera-days, we recorded six species of birds and six species of mammals that visited the focal shrubs, and found that only brown-eared bulbuls Hypsipetes amaurotis removed the fruits. The bulbuls were recorded in all study plots and the median number of fruit taken per visit was 2 (1-6 fruits, n=41). Nearly 80% of the fruits on the shrubs and those on the ground were consumed by brown-eared bulbuls. In some cases, consumption by the birds could not be observed, and was inferred by behavior. These observations suggest that brown-eared bulbuls are the primary seed dispersers, in terms of quantity, for Aucuba japonica var. borealis at the study site. Further studies, such as comparative studies in different forest types, and to examine the annual variation of fruit removal, are recommended to expand the results obtained in this study. We suggest that, for those purposes, camera-trapping is one of the best methods to investigate the fruit removal of Aucuba japonica var. borealis by birds in the field.