Following the flush of spring growth of primary production (the “green wave” hypothesis) has been applied as a universal explanation for spring migration timing of avian herbivores. However, studies of the green wave hypothesis have focused on species feeding intensively on above-ground primary production. To test whether a facultative grazer strictly follows the green wave, we used 16 complete tracks in time and space of spring migrating tundra bean geese (Anser serrirostris)fitted with telemetry devices from two flyways between Yangtze River Floodplain winter areas and Anadyr (Russia)/Central Arctic breeding grounds. We combined these with high spatial resolution MODIS satellite-derived plant production data to relate the timing of spring migration to that of the green wave index (GWI) at different staging regions and on breeding areas. Results showed that, at stopovers south of 52°N, eastern tundra bean geese fed mainly on cropland and arrived at stopover sites ahead of 50% GWI. At all subsequent stopover sites in Russia, eastern tundra bean geese fed exclusively on natural forage land, and followed GWI northwards, finally overtaking GWI to arrive at the breeding sites in advance of these dates. These data show that satellite-derived GWI are generally poor predictors of the arrival dates of spring migrating eastern tundra bean geese, but that deviations related to differential habitat use along the flyway and the need to arrive on the breeding areas ahead of snowmelt to coincide subsequent hatching of goslings with optimal food availability.
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