Birds of the Juruá River: extensive várzea forest as a barrier to terra firme birds

The Jurua River is the third largest white-water tributary of the Amazon River, yet, historically, it has not been considered an important barrier for bird communities. The upper region of the Jurua River was the focus of two ornithological collections in the early twentieth century, but the middle region, where the river and surrounding varzea flooded forest widen, has remained largely unexplored by ornithologists. Inspired by Dr. Emilie Snethlage, whose ornithological expeditions to Amazonian rivers during the early twentieth century were foundational in documenting the importance of river barriers, we undertook a month-long expedition to the middle Jurua River. We collected the first modern specimens, high-quality tissues, and sound recordings of birds from the middle Jurua region. Combining our data with those from previous collections, we present the first comprehensive inventory of bird species from the Jurua region, document several significant range extensions, and report the first evidence that the middle Jurua River acts as a barrier in at least four species complexes of terra firme upland forest birds. Our findings have important taxonomic and biogeographic implications for birds of the Jurua region and southwestern Amazon basin.