Anthropogenic factors negatively influencing the endangered Strange-tailed Tyrant’s breeding success

Abstract

The Strange-tailed Tyrant Alectrurus risora is a threatened grassland bird that experienced a 90% reduction inArgentina. Remaining populations occur in northeastern Argentina where we evaluated the species’ response todifferent factors that could negatively influence its breeding success: increased mesopredator abundance, cattleraising and wildfire occurrence. We conducted our study in two protected areas, Reserva El Bagual (REB) and IberáNational Park (INP), and in several livestock ranches of Corrientes. Mesopredator abundance was higher in INP,where foxes were identified as the main nest predators and where nest predation probability was found to begreater than in REB. Nest success probability and nest density were significantly higher in protected areas than inlivestock ranches. In February 2022, INP suffered a series of wildfires which affected 47% of its surface. We did notfind significant differences in the species’ breeding success before and after the wildfires, yet nest survival tendedto be lower in areas affected by them. These results could be explained by predator-livestock conflicts, which drovetop predators to extinction in Corrientes and possibly triggered a mesopredator release, current livestock practices(as annual-fires and stocking rate) affecting vegetation structure, and a rapid grassland recovery, changes in foodavailability or in the nest predators’ community after the wildfire. Our findings are alarming considering that wefound negative effects on the Strange-tailed Tyrant’s breeding biology both in protected areas of high conservationvalue and in private lands devoted to livestock grazing, the main form of land-use in the region.