In September I visited Java for ten days to see rainforest birds and other wildlife. Java holds special interest for anyone wanting to understand the arcane topic of how Asia and Australia exchanged birds in the past. Its conservation problems are dramatic. The first time I went there I found a dead rhinoceros.
As recently as 10,000 years ago Java, Sumatra and Borneo were part of the Asian mainland because a cooler climate lowered the sea, exposing the Sunda Shelf. Australia is much closer to mainland Asia when seas are lower, at which times the climate is drier as well as cooler, and savannah rather than rainforest may have dominated the Sunda shelf. The eastern half of Java (and its satellite island Bali) are a drier today than Borneo, Sumatra and Malaya, and it is in Java and Bali that we have the best chance of locating the birds that characterised the more open habitats of the Sunda shelf in glacial times.
The golden-headed cisticola, a cute bird with a commanding voice, is an obvious candidate. It is a recent coloniser of Australia that is common in Java and Indochina but absent from Malaysia and Borneo (except as an apparent vagrant). On Sumatra it is believed to be a recent coloniser (MacKinnon & Phillipps 1993) exploiting grassy clearings created by people. While it is possible that this small bird reached Java directly from Thailand, it is more likely that during a glacial period there were mosaics of rainforest and savannah linking Thailand to Java, providing almost continuous habitat for this small grassland bird, which was then able to reach southern Indonesia and Australia.