Dietary ecology of two migrant flycatchers in habitats with and without cattle during the breeding season in central Argentina

Food selection is a key aspect of a bird's life history strategy, so understanding how birds respond to variation in food abundance is relevant to evaluating their general ecology and survival, and also the potential consequences of the degradation of environments impacted by livestock. We studied the dietary ecology of Vermilion Flycatchers (VEFL) and Fork-tailed Flycatchers (FTFL), two insectivores and Neotropical austral migrants, during their breeding season. We worked in areas with and without cattle ranching in the Espinal biome of La Pampa, Argentina. We found different arthropod prey abundance for both flycatchers according to arthropod orders and/or study sites, suggesting that livestock may impact food abundance. Both consumed similar prey and positively selected for hymenopterans and coleopterans, and FTFL also positively selected for orthopterans. VEFL selected nest sites with a lower abundance of heteropterans and FTFL selected sites with a higher abundance of coleopterans. Additionally, VEFL nest survival was negatively related to the abundance of hemipterans and FTFL nest survival was positively related to the abundance of coleopterans. This study helps fill gaps on the general ecology of species that breed in rangelands, and highlights the importance of similar studies to formulate effective conservation planning for the Espinal biome.