We investigated avian frugivory during bird visits to fruiting Prunus verecunda and Swida controversa trees in Ogawa Forest Reserve, Japan, to: (1) quantitatively determine rates of frugivory by each species in a cool temperate forest, and (2) identify how three factors (location at forest edge or interior, crown area, and quantity of mature fruits) affect frugivory. We identified potential frugivores by means of bird fauna censuses and directly observed the frequency of visits to trees (FVT) and the number of fruits removed per visit (NFR) from 15 P. verecunda and six S. controversa trees. Based on our censuses, 18 bird species were predicted to visit P. verecunda during its fruiting period; however, 10 species actually visited, and only four removed fruits. Whereas we predicted that 22 species would visit fruiting S. controversa, 13 species actually visited, and only eight removed fruits. FVT and NFR differed significantly among bird species, and the potential number of fruits removed per hour differed among bird species and between tree species. Different factors affected FVT and NFR and also differed between tree species, probably because of seasonal changes in bird behavior. This study suggests that direct observation is useful for calculating how frugivory differs quantitatively among avian or tree species.
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Vol. 15 • No. 1