Range expansion of the screaming cowbird (Molothrus rufoaxillaris) mediated by a new brood parasite-host interaction in central Chile

The Screaming Cowbird (Molothrus rufoaxillaris) is a brood-parasite specialized in parasitizing the Grayish Baywing (Agelaioides badius). Recently, it started to parasite a new host, the Austral Blackbird (Curaeus curaeus), which has driven the expansion of its range to central Chile. However, its actual and potential distribution and the natural history of this interaction are scarcely known. In this note, we describe the distribution, habitat use and phenology of the species in Chile. Additionally, we present data on feeding events of Screaming Cowbird fledglings by Austral Blackbirds. For doing so, we analyzed data from a citizen-science project using Maxent and Random Forest models. We found that the Screaming Cowbird is distributed mainly in urban and agricultural habitats, avoiding native shrublands and forests. The potential distribution is driven by the temperature and the Austral Blackbird distribution. This note confirms the relationship between both species of icterids and gives new insights into how new host-parasite interactions can drive the range expansion of brood parasitic birds.