DISCUSSION Our results reveal a direct spatio-temporal link between areas identiﬁed at highest HPAI H5N1 risk in India and Bangladesh, in March 2009, and the wild bird outbreaks, in May through July 2009, in China (Qinghai Lake region), Mongolia, and Russia. The spatial prediction of HPAI H5N1 risk was com- paratively less strongly related to duck density in South Asia than it was in Southeast Asia. A strong association between duck and rice farming is observed in Southeast Asia (Gilbert et al., 2007), and an identical association is apparently found in Bangladesh and surrounding regions of northeastern India (Hossain et al., 2005). However, the production systems may differ. Duck and poultry pro- duction in Bangladesh is ubiquitous, and most small farmers keep ducks under a family subsistence level of management (Das et al., 2008). In contrast, duck produc- tion is far more intensiﬁed in terms of ﬂock size, move- ments, and trade in Thailand and Vietnam, with some ﬂocks being moved over 100-km by trucks (Songserm et al., 2006). Duck movement and active trade of products may have contributed to regional HPAI H5N1 spread in Southeast Asia (Thailand and Vietnam) during the ﬁrst two waves of epidemics, which would explain the higher sta- tistical relationship between duck density and HPAI H5N1 presence as compared to South Asia. The South Asia Model provided highest predictive capacity for India and Ban- gladesh (Table 1 and Fig. 1d), but also performed well on the Thailand and Vietnam 2006 outbreaks (Table 1 and Fig. 1; compare red dots in Fig. 1a to predicted risk in Fig. 1d), a period when Thailand focused on active sur- veillance, pre-movement testing, and restricted movements of free-grazing ducks, while Vietnam implemented massive vaccination in chicken and duck populations. We propose that domestic ducks merely act as a reservoir of HPAI H5N1 in South Asia and are less implicated in spread, compared to in Southeast Asia prior to control targeted on ducks. This may explain why a minimal density of domestic ducks is required for persistence, but that their abundance does not proportionally relate to HPAI H5N1 risk. In this study, we used an autologistic regression ap- proach to compare the analysis of Bangladesh and India data to previously published similar models based on Thailand and Vietnam data. Alternative approaches have been used to model the distribution of HPAI H5N1 in other regions (Williams et al., 2008), and distribution Flying Over an HPAI H5N1 Infected Landscape 455 modeling can be achieved through many different statistical techniques (Elith et al., 2006). In particular, the logistic regression framework has its limitations for modeling nonlinearity of effect of the continuous-scale risk factors on the logit form of the outcome variable. Alternative methods such as boosted regression trees (Elith et al., 2008) of maximum entropy models should be considered in future research. Three of the GPS-marked birds stayed for extended periods of time in, or close to, areas of high HPAI H5N1 risk in South Asia, one of them staying at a distance <20 km from a documented concurrent HPAI H5N1 outbreak, prior to undertaking their northward migration, which included stopping over in Qinghai Lake, China. We could not document that these three birds spread HPAI H5N1 from Bangladesh to Qinghai Lake area. In addition, one should note that the bird that stayed closest to a documented HPAI H5N1 outbreak was a Ruddy Shelduck. Recent inoculation experiments carried out on that species resulted in 100% mortality, with birds surviving in rather poor physical conditions, though shedding virus for several days (Kwon et al., 2010). In addition, Kwon et al. (2010) failed to detect H5N1 in a noninoculated Ruddy Shelduck that was in contact with other ones inoculated with HPAI H5N1. So, the available evidence suggests that it is quite unlikely that an HPAI H5N1-infected Ruddy Shelduck could have migrated over such long distances and trans- mitted the disease to conspeciﬁcs. However, daily regional movements for these species may be >100 km per day. GPS-equipped birds represent a tiny fraction of the waterfowl population; we postulate that these birds are indicative of hundreds to thousands of migratory birds that could have been in contact with outbreak sites when poultry outbreaks were taking place in Bangladesh, and could have spread the virus along their northward migra- tion to Qinghai Lake of China and into Mongolia and Russia. On July 27, 2009, an outbreak documented in wild birds at Doroo Lake in central Mongolia, where there are no poultry, was attributed to H5N1, including two Bar- headed Geese marked by our team during the previous year. Furthermore, other waterfowl, including several duck species not studied here, migrate through these regions and may have distinct movement patterns and chronology. Species with different routes and timing may provide more opportunity than we have indicated for exchange of virus among birds or by fecal–oral transmission in wetlands used during migration.