Nest-site features influence nest survival of the Hellmayr's pipit in extensive cattle-grazed grasslands

The Pampas Grasslands in South America have been almost completely transformed by urbanization and agriculture. Many grassland birds persist only in extensive natural pasturelands, which are under constant pressure from fragmentation, cattle-grazing, and exotic plant species. Identifying which habitat features affect bird breeding success is important for their conservation in altered habitats, although few studies have been conducted in the Pampas Grasslands. We analyzed the influence of habitat features on the daily nest survival rates (DSR) of the Hellmayr's pipit (Anthus hellmayri), a grassland passerine endemic to South America, in a cattle-grazed grassland. We evaluated the effects of vegetation features at a nest-site scale, proximity to habitat edges, cattle density, and temporal factors. During 3 breeding seasons (2017-2020), we confirmed the fate of 90 nests, 25 of which were successful (27.8%). Predation was the most common cause of failure (80%), followed by weather-induced abandonment (10.8%). Average DSR was 0.9106, with a cumulative survival probability of only 7.4%. The best model indicated that DSR was higher in nests adjacent to grass clumps than in those placed in depressions and followed a quadratic trend with nest age. Clump nests may be better protected from aerial predators and rainfall; hence pipits could be more successful in areas with more grass clumps. The very low nest success raises concern regarding the value of these grazing fields as breeding habitats; we urge authorities and landowners to increase conservation efforts in the remaining natural grasslands in the Pampas.