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COPYRIGHT 2005 Wilson Ornithological Society
The recent discovery of two species of birds new to science (Ancient Antwren, Herpsilochmus gentryi and Allpahuayo Antbird, Percnostola arenarum) and several others previously unknown from Peru in the white-sand forests of northern Loreto has revealed the presence of an avifauna with close Guianan affinities extending westward from the Iquitos area into eastern Ecuador (Alvarez and Whitney 2003). In the early stages of recognizing this pattern, we focused fieldwork on searches for additional species we predicted to have a high likelihood of occurrence in the various white-sand forest types in this region. Among these was Polioptila guianensis (Guianan Gnatcatcher), a poorly known canopy insectivore represented by about 30 specimens in the world. Its nearest documented point of occurrence lay some 800 km distant along the upper Rio Negro in Brazil near Sao Gabriel da Cachoeira (BMW pers. Obs.).
On 9 September 1997, JAA found what appeared to be Polioptila guianensis in tall, white-sand forest in the proposed Allpahuayo-Mishana Reserve outside Iquitos on the road to Nauta. He noted, however, that the birds' songs differed distinctly from BMW's recordings from Brazil. In subsequent years, we obtained three specimens and a good sample of recordings of the songs and calls of this gnatcatcher, which appears to have a highly restricted distribution, even within the reserve. After comparing our specimens and sound recordings with those of all Neotropical gnatcatcher species, especially P. guianensis from diverse points in its distribution, we are convinced that the Iquitos-area birds are most closely related to P. guianensis, and would best be described as a new species, which we propose to name:
Polioptila clementsi sp. nov.
Iquitos Gnatcatcher
Perlita de Iquitos
Holotype.--Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos (MUSM), Lima, Peru, No. 21113; male (skull unossified) from the Zona Reservada Allpahuayo-Mishana, 03[degrees] 55' S, 73[degrees] 29' W, south bank of Rio Nanay, approximately 25 km wsw of Iquitos, Department of Loreto, Peru; 150 m elevation; 15 December 1998; collected by JAA. Voice specimen of an accompanying individual is archived at the Macaulay Library of Natural Sounds (MLNS), Cornell Laboratory of Ornithology, Ithaca, New York; LNS 120444. A sample of liver tissue was preserved (Alvarez No. 1.12.98) and will be accessioned at the Louisiana State University Museum of Natural Science (LSUMZ) once it is legally exported from Peru.
Diagnosis of Polioptila clementsi sp. nov.--A typical member of Polioptila (sensu Ridgway 1904:710-711), including a thin black bill and graduated tail, with narrow rectrices bearing conspicuous white on the outer three pairs but none on the three central pairs. The following pertains only to males, as we have no specimens of female P. clementsi. Readily distinguished from all congeners except P. guianensis, from which it differs by its significantly longer bill (mean 12.1 versus 11.4 mm; culmen from base at skull). On a taxon-by-taxon basis, differs from P. g. guianensis by uniformly gray throat and breast (instead of throat conspicuously paler than breast) and presence of black bases on outer and penultimate pairs of rectrices, with third pair mostly black (instead of three outer pairs entirely, or almost entirely, white); from P. g. facilis by presence of a conspicuous, broken white eyering (lacking in P. g. facilis) and greater extent of white on outer rectrices (approximately basal 1/3-i/2 black in P. g. facilis); from P. g. paraensis by generally darker and more bluish-gray plumage, and greater extent of white on outer rectrices (approximately basal 1/3-1/2 black in P. g. paraensis). Readily distinguished from P. schistaceigula, the purported closest relative of P. guianensis (Zimmet 1942), by much paler plumage overall and somewhat longer tail with extensive white (rectrices essentially all black in male P. schistaceigula). Males of all other species of Polioptila have discrete areas of black on the head (ranging from streaks to extensive caps) in definitive alternate plumage, among other differences.
Diagnosis of voice.--Loudsong structurally similar to, but immediately distinguished from, all forms of P. guianensis by presence of sharp, "inverted chevron-shaped" introductory notes (virtually always three of these) delivered slowly enough to be counted in the field, followed by a series of evenly spaced notes delivered at a faster pace than by any of the taxa of P. guianensis. The loudsong of P. schistaceigula is a variable set of notes lacking coherent, repetitive structure in series, and is thus very different; other species of Neotropical gnatcatchers are widely and variably divergent in both songs and calls.
Distribution.--Known only from tall, Caraipa-dominated varillal forest (see Habitat and behavior section below) at the type locality (the Reserva Nacional Allpahuayo-Mishana)just west of Iquitos, Department of Loreto, Peru.
Description of holotype.--See color frontispiece. Capitalized color designations (corresponding number in parentheses) from Smithe (1975). Rictal bristles present, inconspicuous. Upperparts from base of bill to uppertail coverts, sides of head, and upperwing coverts essentially uniform and closest to Dark Neutral Gray (83), in some lights appearing slightly more bluish, toward Plumbeous (78). Head lacking discrete areas of black or white except for a narrow, white eye-ring, slightly broken at front and back edges. Throat and breast, including some posterior extension to sides, slightly paler than upperparts (lightest at the lower breast/upper belly), Medium to Light Neutral Gray (84-85). Belly and undertail coverts white. Primaries and secondaries closest to Blackish Neutral Gray (82), outer vanes of primaries finely edged with same gray as upperparts, inner vanes narrowly edged whitish. Alula and smaller, overlying feather blackish with thin whitish margin on outer vane; primary coverts same blackish but lacking whitish margins. Underwing coverts white, the tiny coverts at base of outer primaries and at bend of wing with dark gray centers and whitish tips. Tail full (12 complete rectrices) and unabraded, distinctly graduated. Three inner pairs entirely blackish. Black/white pattern on No. 4 and No. 5 differs on left and right sides of the bird, the right side having somewhat more white, especially on the outer vanes. Rectrix No. 4 mostly blackish with white tip (about 5 mm on inner vanes, to about 10 mm on outer vanes); No. 5 mostly white with approximately basal 1/4-1/3 blackish, on the inner vane extending posteriorly from the rachis to the feather margin in a diagonal strip to invade the white region to within about 15 mm of the tip on the right feather and to within 12 mm of the tip on the left feather. Outer rectrices (pair No. 6) white with about basal 1/5 of outer vane blackish, basal 1/3 of inner vane blackish and showing same diagonal, posterior extension described for No. 5 only to a lesser degree. Rectrices show same pattern on ventral and dorsal surfaces except that No. 4 appears wholly blackish (like the two central pairs, no white tip visible) when viewed from above. Soft parts in life: iris brown, maxilla black with paler commisure, mandible grayish-horn, legs and feet bluish-gray, soles of feet whitish. MUSM 21113 was selected for the holotype because it is in the best condition of the three available specimens, and has a complete and fully grown tail. Its cranium was clear and unossified; thus, it may be a juvenile.
Measurements of holotype.--Wing (chord) 45.4 mm, tail 45.8 mm, culmen from base (at skull) 12.7 mm, bill width at anterior edge of nares 2.3 mm, tarsus 15.3 mm, mass 6.0 g.
Specimens examined.--Only specimens that were measured are listed. Specimens of all other Polioptila species in South America were compared superficially. The sample below was restricted to P. guianensis and P. schistaceigula, the presumed closest relatives of P. clementsi. Some standard measurements of these specimens, with sample sizes, are...
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