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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.

The Picumnus exilis complex is composed of 6–7 subspecies distributed from eastern Colombia, through Venezuela, the Guianas, to northern and northeastern Brazil. They are characterized by a greenish back, whitish or yellowish belly (barred or tainted with black), and males with a red and/or orange forehead. Here we review the taxonomy of this complex based on morphometric and plumage characters from a total of 487 specimens that were analyzed. Eighteen plumage characters were found, of which 12 proved to be informative. The results suggest the existence of five valid taxa: Picumnus exilis (Lichtenstein 1823), a Brazilian endemic found near the coasts of Bahia and Sergipe States; Picumnus pernambucensis Zimmer (1947) another Brazilian endemic occurring north of the Sao Francisco River in the “Pernambuco” Area of Endemism; Picumnus buffonii Lafresnaye (1845) found in the Guiana Shield, east of the Rio Branco and east of the Rio Tocantins on the southern side of the Amazon River; Picumnus undulatus Hargitt (1889) occurring between the Rio Branco, Rio Negro, and Orinoco Rivers, and Picumnus obsoletus Allen (1892) which ranges from the Orinoco Delta north to far northeastern Venezuela. Furthermore, both P. e. salvini Hargitt (1893) and P. nigropunctatus Zimmer and Phelps (1950) proved to be junior synonyms of Picumnus obsoletus Allen (1892). Similarities between the species considered here and other representatives of this genus strongly suggest that the Picumnus exilis complex could also be related to groups of other complexes. This highlights the need for taxonomic reviews to understand the cryptic diversity within the Picumnus genus.