Reappearance of the mangrove rail Rallus longirostris following reinvasion of southern Brazilian salt marshes by the exotic tanner grass Urochloa arrecta

Abstract Biological invasions are a major driver of wetland change, but some non-native species may also provide resources or habitat for native fauna, creating conservation trade-offs. The mangrove rail Rallus longirostris , a bird typically associated with mangroves, was recorded from the 2000s to the early 2020s using patches of the invasive African tanner grass Urochloa arrecta in subtropical salt marshes of southern Brazil. In 2020, management actions eradicated the invaded patches used by the rail, after which R. longirostris disappeared locally. Here, we use continued monthly field surveys from 2022 to 2026 to evaluate the prediction that R. longirostris would reappear only after reinvasion by U. arrecta and the development of patches large enough to provide suitable structure. Urochloa arrecta reappeared as early as 2021, but R. longirostris was recorded again only from mid-2023 onward, when larger patches had developed. By July 2024, three patches occupied by R. longirostris measured 187 m 2 , 198 m 2 , and 1,232 m 2 , whereas a smaller patch of 62.2 m 2 remained unoccupied. The repeated sequence of appearance, disappearance after control, and reappearance after reinvasion strengthens evidence for an association between R. longirostris and the habitat structure provided by U. arrecta . We raise the possibility that observed patch-size pattern reflects a lower patch-size constraint on rail use, but this hypothesis remains to be tested. We also discuss the conservation dilemma posed by an invasive plant that harms native salt-marsh biota while providing habitat for a threatened native bird and propose the ecological trap hypothesis be tested.