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

BROWNE, M.; CATAUDELA, J. F.; DI GIACOMO, A. G.; DI BITETTI, M. S.; DI GIACOMO, A. S.

Gramado

Congreso; II Ornithologicail Congress of the Americas; 2023

The Strange-tailed Tyrant (Alectrurus risora) is a threatened grassland bird that experienced a drastic 90% range reduction in Argentina. Remaining populations occur in the provinces of Corrientes and Formosa in northeastern Argentina where livestock production is the main land-use. Cattle was introduced in Corrientes in the 17th century, while it was introduced in Formosa in the 1930s. Early persecution by farmers drove top predators to extinction in Corrientes, while in Formosa they are extant. In February 2022, the Iberá National Park suffered a series of megafires which affected 47% of its surface. A previous study indicates that Strange-tailed Tyrant females avoid burned patches for 2 years after a fire. We evaluated the Strange-tailed Tyrant’s breeding biology to use as a study case of the response of endemic threatened grasslands birds to different anthropogenic factors. We conducted nest searches, with a total of 172 in REB, 115 in INP, 14 in INP after the wildfire, and 22 in grazing fields monitored throughout the 2015—2022 breeding seasons. During 2015, we conducted a mammal survey in both protected areas (REB and INP) using camera-traps. DSR was modulated by nest age, breeding time and by anthropogenic factor. Estimated nest success values: 20% where top predators are present. 14% where top predators are extinct. 9% after the megafire in INP. 7% in grazing fields. Mesopredator abundance is greater in INP, where top predators are extinct, than inREB, where they are present. Foxes were identified as the main nest predators in INP, where DSR was lower than in REB. Our results could be explained by predator-livestock conflicts, which drove top predators to extinction in Corrientes possibly triggering a mesopredator release. The lower DSR and nest density of grazing ranches could be influenced by current grazing practices, such as annual fires and stocking rates, affecting vegetation structure and food availability. Rapid grassland recovery and a high population density could have allowed the Strange-tailed Tyrant to breed in the subsequent season after the wildfire. Our findings are alarming considering that we found negative effects on the Strange-tailed Tyrant’s breeding biology both in protected areas of high conservation value and in private land devoted to livestock grazing, the main form of land-use in the region.