450 Marius Gilbert et al. and duck density. Human population data were extracted from the GRUMP database (CIESIN et al., 2005). Data on average cropping intensity were derived from annual maps of cropping intensity and paddy rice agriculture, at 500-m spatial resolution, in 2005 using satellite images from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the NASA Terra platform (Biradar and Xiao, 2010). Elevation data was obtained from the GTOPO30 database (LDAAC, 2004). All data were resampled or aggregated at a spatial resolution of 0.04166 decimal degrees (0.041666 dd is approximately 5 km at equator). HPAI H5N1 outbreak data were converted into presence or absence in each pixel, ani- mal and human density data were converted into a number per pixel, and the original 500-m resolution cropping intensity data were aggregated by computing the mean number of cropping season in each 0.04166 dd pixel. Out- break data from Thailand and Vietnam were all geolocated at the subdistrict and commune level, respectively (median size 16 km2). In the other countries, a proportion of the out- breaks were located in EMPRES-I at the village location level, and a fraction was geolocated at the administrative level 3 level. The fraction of allocation to an exact location repre- sented 44%, 100%, 87%, 77%, and 100% for Bangladesh, Cambodia, India, Laos, and Myanmar, respectively. Wildbird Capture and Satellite Telemetry Captures of wild waterfowl were made with monoﬁlament nooses, or by herding birds into corrals during wing molt, when many waterfowl are ﬂightless. We ﬁt birds with solar- powered Platform Terminal Transmitters (PTTs; Micro- wave Telemetry Inc., Columbia, MD). The transmitters weighed 9.5–45 g, and some were equipped with internal GPS receivers, solar panels, temperature and voltage sen- sors, and external antennas. Transmitters were attached dorsally with Teﬂon ribbon (Bally Ribbon Mills, Bally, PA) tied with knots secured by super glue (Henkel Loctite Corp., Rocky Hill, CT). In Qinghai Lake, China, we marked 14 pre-breeding Bar-headed Geese (Anser indicus) in March–April 2007, and 12 postbreeding Ruddy Shelducks (Tadorna ferruginea) in September 2007 (before fall migration starts). We also marked 15 Bar-headed Geese and 4 Ruddy Shelducks in spring 2008 and 10 Ruddy Shelducks in fall 2008. We used 30 g and 45 g backpack GPS Argos solar transmitters (Microwave Telemetry, Inc.). Bar-headed Geese and Ruddy Shelducks were selected for marking, because these species comprised the largest numbers of waterfowl that died in the 2005 outbreak at Qinghai Lake. Tracheal and cloacal swab samples were taken for each bird and stored at 4 C before being frozen in liquid nitrogen (maximum 3 hours post- collection) to test for inﬂuenza A. All the 55 birds appeared healthy, showing no symptoms of inﬂuenza. Twenty-two of 29 marked Bar-headed Geese and 24 of 26 marked Ruddy Shelduck were sampled for avian inﬂuenza virus (cloacal and tracheal swabs, blood serology) following standard procedures (FAO, 2007). Virology analyses, conducted by the Chinese Academy of Sciences, Wuhan Institute of Virology, included: (1) type A inﬂuenza with an ELISA test (Optical Density 630 above 0.23 as positive); (2) H5 sub- type with RT-PCR (Fouchier et al., 2000); and (3) H5, H7, H9, and H10 antibodies with hemagglutinin inhibition (OIE, 2004). One of the samples was positive for inﬂuenza A virus through ELISA, and none were positives by RT- PCR. In India, 15 Bar-headed Geese, 4 Ruddy Shelducks, and 41 individuals of other 8 duck species were marked at Chilika Lagoon and Koonthankulum Reserves during December 2008 and January 2009. All the 61 birds marked with satellite transmitters in India have tested negative through RT-PCR for the H5N1 virus, using a similar sampling procedure as the birds marked in China. Transmitters were programmed to collect GPS loca- tions at 2-hour intervals throughout the 24-hour day, and transmit signals to Argos satellites every 65 seconds for an 8-hour on-cycle, followed by a 48-hour off-cycle to facili- tate solar recharging. Data were recovered from the Argos Data Collection and Location System (CLS America Inc., Largo, MD) via receivers aboard polar-orbiting weather satellites. CLS calculated PTT location estimates that were derived from the perceived Doppler-effect shifts in trans- mission frequency during a satellite overpass. The accuracy of each location was rated by class. Class G locations indicated that the position was a GPS location with mean accuracy ± 18.5 m. Conventional Argos location classes 0, 1, 2, and 3 indicated the location was derived from 4 transmissions, with 1-sigma accuracy >1000 m, 350– 1000 m, 150–350 m, and 150 m, respectively. Location classes A (3 transmissions) and B (2 transmissions) are not assigned accuracy estimates by CLS, and location class Z indicates that no locations were obtained. We compiled and validated our Doppler-derived location data using the Argos Filter Algorithm (D. Douglas, Version 7.03, http://alaska.usgs.gov/science/biology/spatial/). The ﬁl- tering algorithm ﬂags improbable locations based on user-deﬁned distance and velocity thresholds. We used the