Saffron-cowled Blackbirds' reduced nest success in Argentina's agricultural land highlights the importance of non-agricultural habitat for its conservation

The Saffron-cowled Blackbird (Xanthopsar flavus) is a globally endangered icterid endemic to the southern South American grasslands. Temperate grasslands are among the most threatened ecosystems in South America due to their high rate of land use change. In northeastern Argentina, over the last century, the conversion of natural grasslands to livestock farming, croplands, and afforestation has resulted in significant losses of breeding habitat for the Saffron-cowled Blackbird. Consequently, it has suffered severe populational declines, and its remaining populations are fragmented. In order to understand the impact of agricultural systems on the Saffron-cowled Blackbird populations, we studied its breeding biology (clutch size, hatching success, nestling production, and fledgling success) and the main parameters that influence nest survival rate in five breeding habitat types. During the breeding seasons of 2015 to 2019, we located nests and monitored their fate. We found that the cumulative probability of nest survival over the entire nesting cycle (i.e. laying, incubation, and chick rearing) was 0.06, and was lower for nests situated in grazed land covers. Conversely, nest survival was greater in breeding sites without agricultural use, particularly in marshes. Predation was the main cause of nest failure (76%), followed by brood parasitism (10%), and trampling by cattle and agricultural machinery (6%). Brood parasitism rates were higher in grazed paddocks, contributing together with predation to the failure of nests in this habitat. Our findings indicate a negative impact of livestock ranching on Saffron-cowled Blackbird reproduction. Non-agriculture habitats, such as wetlands and flooded areas, are important as refuges for nesting. Thus, the creation of breeding refuges (non-productive sites) within agricultural matrices, in association with biodiversity-friendly agricultural practices, is crucial to ensure the Saffron-cowled Blackbird's maintenance. center dot The Saffron-cowled Blackbird, an endangered icterid endemic to grasslands, has experienced a significant population decline as a result of habitat loss due to land use changes in South America.center dot We located and monitored nests in breeding habitats with different land uses between 2015 and 2019 in Argentina.center dot Nest survival was low overall and decreased with the presence of grazed cover within breeding sites.center dot Nest survival was higher for nests in marshes.center dot The creation of breeding refuges and maintenance of marshes within agricultural matrices are crucial for the species' survival. Xanthopsar flavus es un icterido amenazado y endemico de los pastizales del cono sur de Sudamerica. Los pastizales templados del sur de Sudamerica se encuentran entre los ecosistemas mas amenazados del mundo debido a su alta tasa de cambio de uso del suelo. Durante el ultimo siglo el avance de la industria ganadera, agricola, y forestal sobre los pastizales del noreste argentino ha modificado el habitat reproductivo de Xanthopsar flavus provocando una gran disminucion y fragmentacion de sus poblaciones. Para conocer el impacto que tienen los distintos usos agropecuarios sobre las poblaciones de Xanthopsar flavus estudiamos su biologia reproductiva (tamano de puesta, exito de eclosion, cantidad de pichones y exito de volantoneo), y los principales factores que influyen en la tasa de supervivencia de nidos en cinco tipos distintos de habitats reproductivos. Entre las temporadas reproductivas de 2015 a 2019 localizamos nidos y monitoreamos su destino. Encontramos que la probabilidad de supervivencia de los nidos a lo largo del ciclo de nidificacion (i.e. puesta, incubacion, y cria de pichones) fue baja (0.06), y disminuyo aun mas con la presencia de practicas ganaderas dentro de los sitios de reproduccion. En cambio, la supervivencia de nidos fue mayor en habitats sin uso agricola, particularmente en banados. La depredacion fue la principal causa de fracaso de nidos (76%), seguida por la perdida de nidos debido al parasitismo de cria (10%) y al pisoteo de ganado y maquinaria agricola (6%). La tasa de parasitismo de cria fue mayor en areas con uso ganadero, siendo tan importante como la depredacion en causar el fracaso de nidos ubicados en potreros pastoreados. Nuestros resultados indican que la presencia de ganaderia en el sitio de nidificacion tiene un impacto negativo sobre la reproduccion de Xanthopsar flavus, destacando la importancia de proteger los ambientes no agricolas, como banados y zonas anegadas, como refugios para su reproduccion. Por lo tanto, consideramos que la creacion de refugios reproductivos dentro de matrices agricolas, acompanados por practicas ganaderas que sean amigables con el medio ambiente, es crucial para asegurar el mantenimiento poblacional de Xanthopsar flavus.