Nesting of Chimango Caracaras (Milvago chimango) in nest holes of Burrowing Parrots (Cyanoliseus patagonus) on sea cliffs in Patagonia, Argentina

Patagonia, Argentina The Chimango Caracara (Milvago chimango) is the most abundant member of raptor assemblages from Paraguay and Bolivia to the southern tip of Argentina. In the Argentinian Patagonia we studied nesting of a Chimango Caracara population that uses cavities built by psittacines in a unique ornithological assemblage: 12 km of sea cliffs with 37,000 active nests of Burrowing Parrots (Cyanoliseus patagonus). For 56 days, we monitored 18 active Chimango Caracara nests (11 in 2014 and 7 in 2015). All nests contained plant material inside the holes and had some structure to facilitate landing and perching (balconies, overhangs, or ledges). Most nests were located in the upper third of the cliff and had a single entrance. The average distance to the nearest nest was 108.9 m. We document in detail, for the first time, the nesting of Chimango Caracaras inside cavities. Our results document a new breeding substrate for this species and a nesting behavior unique among Falconidae, which can be interpreted as evidence of adaptability and plasticity of Chimango Caracaras.