Light-level geolocators and species distribution modeling reveal that the Vulnerable Sporophila cinnamomea (Chestnut Seedeater) migrates through the Paraná-Paraguay system to Central Brazil

Abstract

The movement ecology of migratory Sporophila seedeaters in the Neotropics, particularly their migratory routes and nonbreeding areas, remains poorly understood. This study aimed to fill this gap by providing a detailed description of these migratory routes, stopovers, and nonbreeding areas using light-level geolocators on Sporophila cinnamomea (Chestnut Seedeater), a vulnerable species that breeds in southern South America. Species distribution modelling was employed to estimate the probability of occurrence at distribution extremes. Over 3 breeding seasons (October to March 2018–2021), geolocators were affixed to 14 adult males. The overall device recovery rate was 64% (n = 9), and these 8 devices operated, on average, for 301 days. Autumn migration commenced on 24 February, lasting 46 days and spanning 1,679 km, with an average of 2.38 ± 0.92 stopovers—twice the number observed during spring migration (1.40 ± 0.89). We identified 8 nonbreeding areas utilized by the birds for an average of 145 days, primarily located between the northern and northeastern regions of the Paraná and Paraguay Rivers and the southern Tocantins River. Spring migration began in early September, lasted ~58 days, and covered 2,940 km. In both migrations, birds followed routes along the Paraná-Paraguay River valleys, with no significant difference in the number of stopovers detected between seasons. The nonbreeding period model indicated high habitat suitability in 2 regions within the Cerrado biome, particularly a larger area predominantly in the southern and then in the central regions of the Tocantins River. In the southern limit, the breeding model highlighted the most representative area, which is located in the central-eastern region of the Uruguay River. Our study offers valuable insights into the migratory patterns of S. cinnamomea. These findings should be used to inform the planning and establishment of protected areas aimed at conserving grassland species.