According to our analyses, the common ancestor of the reassortant viruses is dated to July 2005 (HPD: April-October), approximately 5 months prior to the first case of human infection caused by the reassortant virus (index case #15 defined by WHO; see Table 1 ). Our analysis of virus phylogeography suggests the ancestors of these reassortant viruses first arose in Greater Jakarta and surroundings, which agrees with the observation that the first two cases of human infection by the reassortant viruses occurred in Central and East Jakarta (index cases #15 and #16). The molecular dating and phylogenetic analyses suggest that nascent reassortant viruses might take several months to spread and expand their diversity in the local bird population, eventually leading to the exposure of human population. The subsequent spread of the reassortant strain seems to become more rapid and extensive, as human cases were reported outside Greater Jakarta one month later, and the reassortant virus spread to as far as the south and east of West Java in the following six months (Table 1 and Figure 4) . Commercial poultry transportation, as well as carriage by migratory birds, may facilitate the viral migration, but their tangible contributions need further studies. Our results suggest that the circulations of reassortant viruses and their genetic parent (group 2) were not restricted by geography within Java. The viral migration back to Greater Jakarta could be driven by the inter-province transfer of infected poultry, in particular the importation of live poultry or fresh poultry products to the densely human populated Jakarta from the remote provinces engaged in poultry-farming. Future studies on economic and social geography (e.g., addressing the modes of inter-provincial poultry transport) in Indonesia might help to further elucidate the effect on the viral dispersal by human, agricultural and industrial activities. In this study, we opted for a lower geographical resolution (i.e., four widely ranged geographical states instead of distinct geographical coordinate for each viral isolate) in our phylogeographic analyses because of the varying precision of the geographical data we have. Therefore, more complex hypotheses of viral origin and migration trajectory cannot be investigated here, but can be explored when more high-quality geographical data of Indonesian H5N1 viral samples is available.