Citizen science reveals climatic and geographical influence in the movement patterns of Hymenops perspicillatus (Spectacled Tyrant), a Neotropical austral migrant

Abstract Tyrannidae represents the largest family among the Neotropical austral migrants, the third most important bird migration system worldwide. Given the difficulty in tracking small birds, the use of citizen-science data emerges as a promising tool for determining the still unknown migration patterns of these species. We assess the migratory patterns of Hymenops perspicillatus (Spectacled Tyrant), a Neotropical grassland tyranid, using eBird data, and provide information for studies that seek to anticipate the impacts of global change—both climatic and anthropogenic—on the avian migratory patterns. Using Kernel analysis, we identified 2 statistical populations (Pampean and Patagonian), on which further modeling was based. We ran generalized additive mixed models to determine the breeding and nonbreeding migratory periods of both populations throughout the year and the role of minimum temperature and precipitation on the presence of H. perspicillatus during the arrival, stay, and departure from breeding sites, and to assess the association of the presence records during migration with geographical landmarks (rivers, coasts, and lakes). Both populations exhibited a clear pattern of latitudinal and longitudinal movement between reproductive and non-reproductive periods. Minimum temperature affected the presences in both populations during arrival, stay, and departure from breeding sites. Precipitation influenced the Patagonian population throughout all periods, whereas the effect for the Pampean population was limited to the pre-breeding migration and part of breeding period. Both populations were associated with large rivers and marine coastlines during pre- and post-breeding migration. Our study provides valuable information on the migratory patterns of a poorly studied grassland migrant, using a novel methodology based on citizen-science data that can be replicated for other difficult-to-track species to elucidate migratory patterns. Considering the impacts of global climate change on avian populations, these studies are relevant for identifying and implementing appropriate conservation measures.