Population dynamics of resident and migratory shorebirds on the southern coast of São Paulo, Brazil

Abstract

Coastal and oceanic ecosystems are essential for aquatic birds, particularly those in the order Charadriiformes, which heavily depend on specific areas for breeding, feeding, and migration. These birds, are particularly representative in coastal environments. In the State of São Paulo, studies on coastal birds are limited, especially in the central coastal region. This study aimed to analyze the dynamics of resident and migratory shorebird populations on the beaches of Peruíbe and Itanhaém, SP, and to evaluate their abundance patterns. From August 2019 to December 2020, we conducted 92 sampling events, recording 24 species of shorebirds, distributed across four families. Among these, there were three resident species, 20 migratory species from the Northern Hemisphere, and one migratory species from the Southern Hemisphere. The samples were dominated by Charadrius semipalmatus (recorded in 61.6% of samples), Calidris alba (11.3%), Tringa melanoleuca (7.3%), and Pluvialis dominica (5.8%). The Shannon-Wiener diversity index varied, with a minimum value of H′ = 0.363 in March 2020 and a maximum of H′ = 1.929 in September 2019. These variations are expected, as March marks the return of Northern Hemisphere migratory birds to their breeding areas, while September coincides with the arrival of these species in the Southern Hemisphere. Cluster analysis revealed three groupings. Group I consisted of dominant and abundant species (C. semipalmatus, C. alba, T. melanoleuca, P. dominica, and C. fuscicollis). Group II consisted of resident species and one migratory species (H. palliatus, H. melanurus, C. collaris, and C. canutus), which were dominant but less abundant. Group III contained species observed in smaller numbers and with lower frequency (1.1-9.8%). The increase in Charadriidae and Scolopacidae on the beaches of Peruíbe and Itanhaém during spring suggests that these areas are important stopover sites in southeastern Brazil, especially for species migrating south, confirming their role as stopover and wintering sites, particularly for Charadrius semipalmatus, Calidris alba, Pluvialis dominica, and Tringa melanoleuca.