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Aim In the Northern Hemisphere, bird migration from the tropic to the temperate zone in spring is thought to proceed at a rate determined in large part by local phenology. In contrast, little is understood about where birds go or the factors that determine why they move or where they stop during the post‐breeding period. Location Study sites were in Oregon, Nebraska and Vermont, and location data we collected extend south to Argentina. Methods We deployed light‐level geolocators on individual Bobolinks from three populations across the breeding range and compare their southbound movement phenology to austral greening as indicated by the Normalized Difference Vegetation Index. Results Bobolinks from all breeding populations synchronously arrived and remained for up to several weeks in two sequential, small non‐breeding areas that were separated by thousands of kilometres, before staging for pre‐alternate moult. Similar to the migration patterns of birds to northern breeding areas, movements into the Southern Hemisphere corresponded to increasing primary productivity. Main conclusions Our findings suggest that the Bobolink's southbound migration is broadly constrained by resource availability, and its non‐breeding distribution has been shaped by the seasonal phenology of grasslands in both time and space. This is the first documentation of individual birds from across a continental breeding range exhibiting phenological matching during their post‐breeding southward migration. Known conservation threats overlap temporally and spatially with large concentrations of Bobolinks, and should be closely examined. We emphasize the need to consider how individuals move and interact with their environment throughout their annual cycle and over hemispheric scales.

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Identifying the determinants of habitat quality for a species is essential for understanding how populations are limited and regulated. Spatiotemporal variation in moisture and its influence on food availability may drive patterns of habitat occupancy and demographic outcomes. Nonbreeding migratory birds in the neotropics occupy a range of habitat types that vary with respect to moisture. Using carbon isotopes and a satellite-derived measure of habitat moisture, we identified a moisture gradient across home ranges of radio-tracked Northern Waterthrush (Seiurus noveboracensis). We used this gradient to classify habitat types and to examine whether habitat moisture correlates with overwinter mass change and spring departure schedules of Northern Waterthrush over the late-winter dry season in the tropics. The two independent indicators of moisture revealed similar gradients that were directly proportional to body mass change as the dry season progressed. Birds occupying drier habitats declined in body mass over the study period, while those occupying wetter habitats increased in body mass. Regardless of habitat, birds lost an average of 7.6% of their mass at night, and mass recovery during the day trended lower in dry compared with wet habitats. This suggests that daily incremental shortfalls in mass recovery can lead to considerable season-long declines in body mass. These patterns resulted in consequences for the premigratory period, with birds occupying drier habitats having a delayed rate of fat deposition compared with those in wet habitats. Taken together with the finding that males, which are significantly larger than females, are also in better condition than females regardless of habitat suggests that high-quality habitats may be limited and that there may be competition for them. The habitat-linked variation in performance we observed suggests that habitat limitation could impact individual and population-level processes both during and in subsequent periods of the annual cycle. The linkage between moisture and habitat quality for a migratory bird indicates that the availability of high-quality habitats is dynamic due to variation in precipitation among seasons and years. Understanding this link is critical for ascertaining the impact of future climate change, particularly in the Caribbean basin, where a much drier future is predicted.