We studied avian dispersal of seeds from the hemiparasitic mistletoe Plicosepalus acaciae (Loranthaceae) to its tree hosts Acacia raddiana and A. tortilis in the Syrian–African Rift (Arava) valley, Israel. The Yellow-vented Bulbul (Pycnonotus xanthopygos) was the sole avian visitor observed feeding on mistletoe fruits. Bulbuls consumed mistletoe fruits whenever they were available, but the fruits only constituted a significant portion of the diet (71% of foraging attempts) when they were most abundant. These birds are potentially good dispersal vectors of P. acaciae because they swallowed the fruit whole and defecated viable seeds that were covered in a viscid pulp, which allowed the seeds to adhere to substrates when voided. In addition, bulbuls spent a large proportion (66–93%) of total observation time perched in Acacia trees, allowing for directed dispersal. Ephemeral river valleys (wadis) with high mistletoe infection were adjacent to those containing no infections, demonstrating that mistletoe dispersal is common within, but not among wadis. This is consistent with the flight behaviour in bulbuls, which do not typically move among wadis. We combined data on bulbul movements between Acacia trees with transit times of mistletoe seeds to create a hypothetical seed shadow as a function of distance from the parent mistletoe plant. Because they are directed dispersers, the movement patterns of bulbuls may explain the current distribution of P. acaciae in the Arava valley.
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We thank Thomas Rödl and Iris Musli for assistance with many aspects of this research and Berry Pinshow for the use of his laboratory. Financial assistance came from Keren Keyemet L’Israel and DISUM grant 00046A from the German Ministry of Environmental Affairs and the Israeli Ministry of Science to D. Ward, Sigma Xi and NSF pre-doctoral fellowships to A.K. Green, and a Claude Leon Foundation postdoctoral fellowship to M.E. Griffiths.
Communicated by T. Friedl.
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Green, A.K., Ward, D. & Griffiths, M.E. Directed dispersal of mistletoe (Plicosepalus acaciae) by Yellow-vented Bulbuls (Pycnonotus xanthopygos). J Ornithol 150, 167–173 (2009). https://doi.org/10.1007/s10336-008-0331-9
- Directed dispersal
- Foraging behaviour
- Negev desert
- Seed shadow
- Transit time