Nesting biology of the Blue-and-yellow Tanager ( Rauenia bonariensis ) in a native woodland of east-central Argentina

Detailed studies on avian breeding biology provide key insights into life history evolution and are essential for conservation. However, breeding biology remains poorly documented for many bird species inhabiting southern temperate woodlands. We investigated the breeding biology of the Blue-and-yellow Tanager (Rauenia bonariensis), including nest characteristics, nest success, nest survival, seasonal variation in nest success, and the effects of brood parasitism and Philornis spp. ectoparasitism, by monitoring 55 nests over three breeding seasons (2015–2018) in native woodlands of east-central Argentina. The breeding season extended from early November to mid-February, with nests built exclusively in the native tree species Celtis tala and Scutia buxifolia. Apparent nest success was 29%, whereas estimated nest survival was 19%, with predation being the main cause of nest failure (36%). Nest success was higher early in the breeding season, whereas nest failure due to Philornis spp. ectoparasitism increased later in the season. Shiny Cowbird (Molothrus bonariensis) brood parasitism affected approximately 30% of nests and significantly reduced egg survival. Our findings provide the first comprehensive description of the breeding biology of this species and improve our understanding of avian reproductive performance in the threatened native woodlands of east-central Argentina.