Description of seasonal patterns of migratory birds in the Pantanal wetland

Abstract Migratory birds rely on habitats along their routes for rest, refueling, and reproduction. They adjust timing, speed, and stopover use to reduce energy and survival costs while maximizing reproductive success. This synchronization with resource availability defines the “critical periods” essential for migration success. Despite awareness of these needs, spatial and temporal patterns of migratory bird movements remain understudied, even for well-known species. This study identified critical periods for migratory birds in the Pantanal and discusses conservation implications. A dataset was compiled using records from biological collections and citizen science platforms. Species were grouped into ecological categories based on shared traits. Twenty ecological groups were identified, with five additional species analyzed separately. Weekly relative frequency of records was calculated by dividing each species’ records by total bird records per week. Generalized Additive Models (GAM) were applied to detect sustained periods of high relative frequency, defined as “critical periods.” Most groups and species exhibited critical periods during the rainy season (weeks 1–8 [Jan-Feb]; 45–53 [Nov-Dec]) linked to resource surges from flood pulses in Pantanal. However, some groups, like open-area insectivores, peaked during the dry season (weeks 30–40 [Jul-Sep]), indicating differing resource-use strategies. Recognizing these critical periods allows for targeted conservation and management during key vulnerability windows, ensuring migratory birds encounter essential resources in the Pantanal to complete their migratory cycles and maintain viable populations.