New breeding colony and notes on the reproductive activity of scarlet ibis (Eudocimus ruber) in Brazil’s World Heritage site

Abstract The Scarlet Ibis ( Eudocimus ruber ) is recognised for its vivid scarlet colour and inhabits various wetland environments in South America. Historically, Scarlet Ibis populations were common along the coast of southern and southeastern Brazil until the 19th century. However, dramatic population declines during the 20th century led to the species' regional disappearance. In February 2025, we opportunistically recorded a new breeding colony of Scarlet Ibis at the São Paulo and Paraná states limits. The colony covers an area of ​​approximately 2 ha, with mostly nests built in mangrove trees ( Rizophora mangle ) above the water body. We estimated approximately 40 active nests, but the colony reaches four times the number of nests observed (approximately 200) during the breeding seasons, according to the local community. We observed different reproductive stages, with five nests containing eggs, two nests had nestlings at varying developmental stages, and one nest appeared to be inactivated. Identifying this new Scarlet Ibis breeding colony enhances our understanding of the species' current distribution and reproductive behavior, guiding new conservation efforts in that region.