A NEW SPECIES OF THAMNOPHILUS ANTSHRIKE (AVES: THAMNOPHILIDAE) FROM THE SERRA DO DIVISOR, ACRE, BRAZIL

Auk, The, Oct 2004 by Whitney, Bret M, Oren, David C, Brumfield, Robb T

ABSTRACT.-

We describe a new species of Thamnophilus antshrike - T. divisorius (Acre Antshrike) - from the Serra do Divisor of Acre, Brazil. The new species is known from a single small ridge (though we expect that it is present on other, unexplored ridges in the Acre Arch uplands), and is common in the interior of shrubby woodlands on poor soil physiognomically similar to white-sand habitats in the Guianas and Amazonia. Thamnophilus divisorius is sister to T. insignis (Streak-backed Antshrike), a narrow endemic of pantepui, and forms a wellsupported clade with that species and T. amazonicus (Amazonian Antshrike). Thamnophilus divisorius occurs in a remote region within a national park in Brazil; despite its limited range, we are optimistic about its future survival. Received 16 May 2003, accepted 24 June 2004.

RESUMO.- Descrevemos uma nova espécie de tamnofilideo (Thamnophilus divisorius, Chocado-Acre) oriunda da serra do Divisor, Acre, Brasil. A nova espécie é conhecida de apenas um único cume de serra (embora é esperada existir em outras áreas similares ainda näo pesquisadas nos arredores), e é comúm no interior de bosques de vegetação baixa crescendo em solos pobres que lembram habitats de campina de areia branca e vegetaçães afins nos Guianas e na Amazônia. É filogeneticamente mais próximo de Thamnophilus insignis (Choca-de-Roraima), espécie de distribuição restrita à região de pantepui, e forma um clade com Thamnophilus amazonicus (Choca-canela). Thamnophilus divisorius ocorre numa região remota dentro de um parque nacional e, apesar de ter uma distribuição extremamente restrita, estamos otimistas sobre a sua sobrevivência no futuro.

IN JULY 1996, the field phase of a management plan for the Parque Nacional da Serra do Divisor (PNSD) in Acre, Brazil, was initiated. The project was funded by The Nature Conservancy International of Alexandria, Virginia, and coordinated in Brazil by the national office of The Nature Conservancy in Brasilia, D.F., the nongovernmental organization S.O.S. Amazônia in Rio Branco, Acre, and the national and regional offices of the Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis (IBAMA). One key aspect of the project was a rapid ecological evaluation (REA; Sobrevila and Bath 1992) of the park's flora and fauna. The ornithology section of the Museu Paraense Emilio Goeldi (MPEG) in Belém, Pará, was responsible for the avifaunal inventory; B.M.W., D.C.O., and the technician D. C. Pimentel Neto conducted the field work. Although the first phase encompassed only 18 field days, with observations divided among six sites in the northern sector of the park, we documented several species of birds previously unknown or poorly known in Brazil, including a striking Thamnophilus antshrike new to science, which we propose to name:

Thamnophilus divisorius sp. nov.

Acre Antshrike

Choca-do-Acre (Portuguese)

Holotype.-MPEG no. 52754; adult male, from Morro Queimado, in the Serra da Jaquirana (one of the easternmost ridges in the Serra do Divisor), above the left bank of the rio Moa in Parque Nacional da Serra do Divisor, Municipality of Mâncio Lima, Acre, Brazil (07°26'36''S, 73°40'28''W); ~500 m; collected 10 July 1996 by B.M.W., prepared by D. C. Pimentel Neto. Tape-recorded by B.M.W., Macaulay Library of Natural Sounds (MLNS), Cornell Laboratory of Ornithology, Ithaca, New York, no. 79060; Arquivo Sonoro Elias P. Coelho (ASEC), Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil, no. BMW 054/10; and Isler inventory, Alexandria, Virginia, no. BMW.125:21.

Diagnosis: Morphology.-Allocation of the new species to the genus Thamnophilus is difficult to justify objectively on the basis of morphology, because characters of diagnostic value have not been identified for the genus and because the present group of ~25 species (as currently classified) may not be monophyletic. The type species of Thamnophilus is T. doliatus (Barred Antshrike), which is barred black-and-white in the male plumage, and mostly rufous-brown in the female plumage. These factors notwithstanding, the new species is most similar morphologically to members of Thamnophilus. Adult males are readily distinguished from other Thamnophilus species by a combination of the following characters: entirely dark-bluish-gray plumage with somewhat blacker hood, wings, and tail, and mottled grayish (rather than mostly white) underwing coverts. Adult females differ distinctively from other Thamnophilus species in having almost uniformly bluish-gray facial region and upperparts with slightly darker wings and tail, and entirely brownish-orange underparts. Both sexes may show minute pale spots (white in male, buff-orange in female) at tips of some upperwing coverts; both sexes have small but more conspicuous spots at the tips of the outer two rectrices; those are reduced to fringes or are absent on the next one or two rectrices.

Diagnosis: Voice.-The loudsong (following Willis 1967) of T. divisorius is similar in pattern, structure, and auditory quality to that of T. doliatus (especially the nominate form), which aligns T. divisorius more objectively with the genus Thamnophilus than does its morphology. That alignment is supported anecdotally: on the morning of its discovery, T. divisorius was heard and tape-recorded by B.M.W. for nearly an hour before being seen, and it was clear from its song that it was an unnamed Thamnophilus antshrike. Thamnophilus divisorius' loudsong differs from the song of all other Thamnophilus species by the following combination of characteristics: (1) it accelerates in pace (progressively shorter internote intervals) for approximately half its duration, slowing slightly and gradually through the final two or three notes; (2) its terminal note, and often the penultimate note, is louder, longer, and of slightly higher peak frequency than the rest of the series, but does not differ dramatically in structure or tonality. Recorded calls appear to be less clearly differentiated from those of several other Thamnophilus species.