Where There Was Fire… Changes in the Community of Nest Predator in Burned Grasslands of the Southern Pampas, Argentina

ABSTRACT

Fire plays a key role in grassland ecosystems by modifying vegetation structure and, consequently, influencing predator–prey interactions that can affect the reproductive success of grassland birds. The reduction in vegetation density and height resulting from fire affects the reproductive success of birds by increasing the likelihood of nest predation and may modify the relative importance of different predator types to nest fate. Streams grasslands are preferred breeding sites for grassland birds in the Southern Pampas of Argentina, in a context of intensive agriculture and grazing. We investigated how post‐fire vegetation recovery influences the relative importance of different nest predators. We displayed 48 artificial nests in burned and unburned streams during the first and second years after fire. Principal Component Analysis (PCA) was used to characterize vegetation structure and Bias‐reduced Logistic Regression to evaluate predator‐specific predation probabilities. Total vegetation cover was significantly reduced in burned streams during the first year, followed by significant recovery in the second year, particularly in the tallest strata. PCA revealed a strong gradient of vegetation height and structural complexity that was closely associated with nest‐failure patterns. Predation attributed to olfactory predators (medium‐sized mammals) was associated with tall and dense vegetation in unburned streams, whereas predation by visual/thermal predators (snakes, birds, and small mammals) was more frequent in burned streams characterized by open vegetation. Furthermore, predation by visual/thermal predators was significantly more likely in burned than in unburned streams. These patterns became less pronounced as vegetation recovery followed the year. Our results are consistent with the idea that fire‐driven vegetation succession acts as an ecological filter, mediating nest predation through shifts in predator‐specific detection opportunities. This sensory‐based segregation of predator activity may represent an important mechanism linking fire, vegetation structure, and reproductive success in grassland birds, with implications for grassland management and bird conservation.