456 Marius Gilbert et al. Three conditions would have been necessary to allow this to happen. First, birds would need to be infected shortly before their departure so to arrive at a time when they were still shedding virus; second, exposed and infected birds must have maintained their ability to migrate. Third, other susceptible birds must be present when infected birds arrive at the Qinghai region or Mongolia. The ﬁrst and third conditions are both plausible: Our results indicate that many birds could have departed from a high HPAI H5N1 risk area in Bangladesh or India at the time of concurrent outbreaks, some of which may have been in- fected. Upon arrival in Qinghai Lake or Mongolia, trans- mission to other birds would have been facilitated by the high densities and aggregation of birds, and the relatively cold temperatures that favor persistence of the virus in the environment (Brown et al., 2007; Rohani et al., 2009). With regard to migration capacity, recent inoculation experi- ments of wild waterfowls with HPAI H5N1 virus indicate a high variability in the pathobiology of infections (Kwon et al., 2010), depending on species. Only a limited number of species have been tested so far, and more detailed studies on the pathobiology of HPAI H5N1 and their capacity to transmit the virus to conspeciﬁcs of other species would shed more light on their capacity to transmit the virus over long-distances. Despite these uncertainties, given that some species of experimentally infected wild waterfowls do not become symptomatic, or are asymptomatic for days (3– 7 days) before becoming symptomatic, one cannot exclude that exposed wild birds of less susceptible species could make long migratory movements of hundreds to thousands of kilometers (Gaidet et al., 2010). Furthermore, the indi- vidual ability to perform long-distance migration may be less critical to virus spread when large numbers of water- fowl are migrating along the same route and may infect each other in a series of infection cycles. Finally, recent information suggests that exposure to low pathogenic avian inﬂuenza viruses provides possible resistance to HPAI H5N1, making migration more easily feasible for infected birds (Kalthoff et al., 2008). We conclude that all three conditions could have been met in spring 2009 to support introduction of HPAI H5N1 to the Qinghai Lake region by migratory waterfowl from a region of high HPAI H5N1 risk in domestic poultry in South Asia. This link between HPAI H5N1 viruses circulating in South Asia, Qinghai Lake area of China, Mongolia, and Russia, (Fig. 2a, Table S3) is consistent with phylogenetic studies that report a high homology between HPAI H5N1 isolates found in northeast India in 2007 and viruses isolated from wild waterfowl in Russia, China, and Mongolia (Wallace et al., 2007; Mishra et al., 2009). Our study highlights the potential for integrating HPAI H5N1 risk modeling with wild waterfowl migration ecology data to map and track (and potentially forecast) hot-spots, introduction, persistence, and spread of HPAI H5N1 along the Asian ﬂyways. In this study, we failed to integrate the temporal dimension in the HPAI H5N1 risk modeling and this limits the applicability of this type of model for establishing areas and time at risk of HPAI H5N1 infection. For example, we found that a Ruddy Shelduck spent several weeks in an area at risk, but in the absence of an explicit reference to time in the model, it is only because it stayed at <20 km from a documented concurrent HPAI H5N1 outbreak that we could consider that it was at high risk of infection. Future research would hence gain from the development of space–time statistical models that could generate not only ‘‘hot-spots’’ but also ‘‘hot-times’’ pre- dictions to be matched against wild bird space–time data. ACKNOWLEDGMENTS This study was supported by grants from the U.S. National Institutes of Health (R01-TW007869), the U.S. National Aeronautics and Space Administration (NNG05GH80G), and the Food and Agriculture Organization of the United Nations (FAO/UN) AGAH-EMPRES Wildlife Unit; dona- tions from the governments of Sweden, Canada, and the United Kingdom; the U.S. Geological Survey Avian Inﬂu- enza Program, and National Science Foundation Small Grants for Exploratory Research (0713027). Additional support was also provided by the Max Planck Institute for Ornithology, Germany, and the Biotechnology and Bio- logical Sciences Research Council, UK (BB/F015615/1). We thank J. Domenech, J. Lubroth (FAO Animal Health Service and EMPRESS Program), S. Haseltine, R. Kearney, P. Bright, S. Schwarzbach, and J. Howell of USGS for supporting this project. We thank Martin Wikelski (Max Planck Institute for Ornithology), Charles Bishop (Univer- sity of Wales, Bangor), and Patrick Butler (University of Birmingham, U.K) for the contribution of transmitters and migration pathways of geese from India. Bird capture and marking was conducted under the USGS Western Ecolog- ical and Patuxent Wildlife Research Center’s Animal Care and Use Committee Review. For ﬁeld assistance with wild bird studies in India, we thank S. Heath (USGS), L. Hawkes (UWales), T. McCracken (UNFAO), P. Sathiyaselvam