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Saturday, February 18, 2006

Yellow-vented Bulbul does swallow some fruits but not others

Yellow-vented Bulbul does swallow some fruits but not others

In an earlier posting it was said that Yellow-vented Bulbul (Pycnonotus goiavier) does not swallow Alexandra palm (Archontophoenix alexandrae) fruits. It pecks on the outer pulp, leaving the fruit on the branch with patches exposing the seed.

With the MacArthur palm (Ptychosperma macarthurii) (above), I have noticed that this bird does swallow the fruits whole. Although I have not seen it regurgitating the seeds, I did find a few patches of faeces with seeds on my driveway. It is possible that the bulbul passed out the seeds?

However, I have been puzzled by the presence of many individual seeds of this palm, cleaned of pulp, scattered along my driveway (left). I do not grow this palm in my garden. These seeds must have been regurgitated by some birds. Can it be the Pink-necked green Pigeon (Treron vernans) that regularly perch on the overhanging ceram palm (Rhopaloblaste ceramica) fronds?

And why does the bulbul swallows fruits of the MacArthur palm but not those of the Alexandra palm? The answer lies in the size of the two seeds. Alexandra palm fruits are nearly round, 12x10 mm, with a single large round seed that is about 9x8 mm in dimension. The flesh is a thin layer of 2-3 mm thick. Although the fruit of the MacArthur palm is of similar size, the seed is very much smaller. It is 10 mm long but only 5 mm broad.

Obviously we have much to learn about the feeding habits of our common birds.

Transverse sections of fruits of MacArthur (left) and Alexandra (right) palms.

Seeds of MacArthur (left) and Alexandra (right) palms.

Scale in mm.
All images by YC.



At 12:25 pm, Anonymous Anonymous said...

I think the Macarthur/Alexander difference is simply fruit size: the bulbuls can just swallow the former and cannot quite swallow the latter. Starlings and koels swallow the Alexander fruits whole and I suspect koels regurgitate the seeds in groups - they even do this with figs!


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