Climate and not latitude seems to determine nesting phenology in Spizaetus isidori

Birds must adjust their breeding phenology to environmental variation and resource availability to maximize their fitness. In temperate climates, birds reproduction is usually seasonal and changes latitudinally. In the Neotropics, these patterns are less clear with some species having marked breeding seasonality and others a less clear pattern. The Black-and-chestnut Eagle (Spizaetus isidori) is a South American endemic, classified as Endangered according to the IUCN. It inhabits forest in the Andes slopes from Colombia and Venezuela to northern Argentina. Here we analyze relationships between latitude, bioclimatic variables from Wordclime and breeding phenology in this species. We estimated laying date for 18 breeding events from 10 different breeding pairs from Colombia, Ecuador, Bolivia and Argentina. Laying date in nests located in the three last countries were between ends of April and mean June without clear variation despite large latitudinal differences. Nests from Colombia showed much larger variation with earlier laying dates in nests in Cordillera Occidental, very late laying dates in Cordillera Oriental and great variation in nests located in the area where Oriental and Central Cordilleras diverge. Precipitation in the wettest quarter was related to laying date. Therefore, climatic factors and not latitude seem to explain breeding phenology in this species.