Seed dispersal by wintering birds in an urban space and relationship between gape width and fruit size

Hamao Shoji, Miyashita Tomomi, Hagiwara Shinsuke, Mori Yoshihisa

doi:10.3838/jjo.59.139

We investigated seed dispersal by wintering birds in an isolated urban green space in Tokyo. Seeds of nine plant species were found in the faeces of eight species of captured birds. The Brown-eared Bulbul Hypsipetes amaurotis, the Dusky Thrush Turdus naumanni and the Japanese White-eye Zosterops japonicus excreted 93% of the seeds, and these birds are dominant in the study site, suggesting that they are important seed dispersers. With the exception of one plant species, all the seeds found in the faeces of the captured birds were from plants growing in the study site, indicating that seeds were only rarely imported from outside of the green space. The faecal samples showed birds to have eaten fruits that were not only smaller but also larger than their gape width. Idesia polycarpa for example had fruits with diameters larger than, and not overlapping with, the gape width of the Red-flanked Bushrobin Tarsiger cyanurus, the Japanese White-eye and the Black-faced Bunting Emberiza spodocephala, indicating that birds can swallow fruits that are larger than their gapes. This finding may be caused by limitation of fruit-size selectivity of birds due to the small area of the isolated habitat and to the end of the fruit season.

Seed dispersal by wintering birds in an urban space and relationship between gape width and fruit size

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