A recent taxonomic revision of the Polioptila 4 guianensis (Guianan Gnatcatcher) complex suggested that at least four allopatric species should be recognized in this morphologically and vocally conserved group: P. guianensis (Guianan Gnatcatcher), P. clementsi (Iquitos Gnatcatcher), P. facilis (Rio Negro Gnatcatcher), and P. paraensis (Para Gnatcatcher) (Whitney and Álvarez 2005). Based on sight-records of a member of the P. guianensis group west of the Rio Madeira, these authors predicted that “an undetected population inhabits most of the region west of the Madeira north of about 7 o S, west to Peru; it should be sought especially in forests growing on white sand and extensively weathered clays (both patchily distributed terra fi rme habitats)”. During the intervening years, AW, BMW, and AA have gathered multiple additional recordings of “Guianan Gnatcatchers” from diverse points in the range of the complex (Whittaker et al . 2008; Whittaker 2009), and, on 4 and 5 July 2007, AA and AW collected and tape-recorded, respectively, the fi rst two specimens from west of the Rio Madeira, which proved to be phenotypically and genetically distinct from other taxa in the P. guianensis complex, justifying recognition of this population as a new species, which we propose to name:
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