The Island Biogeography of Birds on the Wakatobi archipelago

The white-eye populations from all four major islands are morphologically distinct from each of their neighbours

The white-eye populations from all four major islands are morphologically distinct from each of their neighbours

Recent work on bird populations on the Wakatobi archipelago has revealed that many smaller bird species are morphologically and genetically distinct from their mainland relatives. The outcome of this work could be that the Wakatobi islands qualify for Important Bird Area status.

Since 1999, we have been making occasional visits to islands in the south-eastern corner of Sulawesi, initially under an MOU between Trinity College Dublin and the Wakatobi Regency and with support from Haluoleo University in Kendari and more recently as part of the Bogor Agricultural University (IPB Bogor) and University of Hull research programme covering the islands of SE Sulawesi.

We have been focussing our investigations on the bird populations there, and have been mist-netting birds during these visits. This has provided us with a wealth of morphological data (over 1900 individuals) from more than 60 bird species caught on 12 different islands (including Buton, Kabaena, mainland Sulawesi).

After the status of the new species is confirmed, the Wakatobi islands will be able to lay claim to at least three endemic bird species

Sample recordings were made on each island, near the netting sites. This has allowed us to embark on phylogenetic analyses of the local bird populations to complement our morphological studies. The genetic studies are rewriting the textbooks: there are manuscripts in preparation to describe three new bird species from the Wakatobi islands (Wangi-wangi, Kaledupa, Tomia and Binongko, as well as Hoga).

Smaller bird species on Wakatobi

There are consistently different patterns between Buton/Sulawesi populations and Wakatobi populations that demonstrate a lack of mixing. This lack of mixing leads to reproductive isolation of the Wakatobi populations from the mainland and justifies their separation as full species.

In addition, a new, endemic resident species on Wangi-wangi was discovered in 2003. This new species has yet to be formally identified or named, as currently, no specimens exist in any museums. After the status of the new species is confirmed, the Wakatobi islands will be able to lay claim to at least three endemic bird species. That will qualify the Wakatobi islands for Important Bird Area (IBA) status under BirdLife International criteria, assuming all of the endemic bird species are considered to be “vulnerable” or “endangered”. If that does happen, the Wakatobi islands will instantly become Sulawesi’s most important IBA.

Differences between islands

While taxonomic categorisation is an essential aspect of any study, it is usually just the beginning. This has proven to be the case in the Wakatobi islands too. Once visits had been made to each of the four major islands on the Wakatobi, it became clear that each of the islands supported different numbers of the various species.

Even some satellite islands of the major islands differed in terms of the number of species present, and their relative abundance. These differences can provide insights into evolutionary processes and the types of barriers that isolate populations. For example, Wangi-wangi’s endemic white-eye (currently without an official name) occurs only on the island of Wangi-wangi, despite there being two satellite islands within 1km of the shore of that island.

Wakatobi Flowerpecker

Wakatobi Flowerpecker

By contrast, the Wakatobi-wide white-eye (due to be renamed in 2013) occurs on Wangi-wangi and its satellite islands. The beak shape of the Wakatobi-wide white-eye differs between Wangi-wangi and the satellite island of Oroho. This difference is due to competition for food between the two white-eye species on Wangi-wangi and is an example of character displacement.

In addition to such examples of localised competition, there is evidence of much wider scale effects on some of the bird populations across the archipelago. The white-eye populations from all four major islands are morphologically distinct from each of their neighbours. While these differences are ultimately the result of competition, it appears that the driving force behind them is human impact on the islands. That means human influences may be accelerating evolution! That would be a truly remarkable discovery.

Similar investigations (including studies on the Galapagos islands) have only shown human influence to slow the processes that lead to speciation. The work to date serves to highlight the possibilities for study within the terrestrial habitats of the Wakatobi and demonstrate the archipelago’s potential as a living laboratory.

The Wakatobi is just one archipelago within the 17,000 islands of Indonesia and there are other islands in south-eastern Sulawesi that still have poorly documented avifaunas. While ornithologists added 71 new species to Indonesia’s bird list between 1992 and 2007 (Indonesian Bird Checklist no. 2), it looks like there are still a few more to find.

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