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Chestnut-backed Antbird Poliocrania exsul

  • Order: Passeriformes
  • Family: Thamnophilidae
  • Polytypic: 5 subspecies
  • Authors: Woltmann, Stefan, Ryan S. Terrill, Matthew J. Miller and Matthew L. Brady
Sections

Systematics

Geographic Variation

Five subspecies recognized (Dickinson 2003, Zimmer and Isler 2003). Variation relatively slight and clinal among some subspecies, mainly related to (a) presence or absence of white spots on greater coverts (maculifer, cassini), and (b) female underpart coloration. Darkness of upper parts varies subtly. Differences in morphometric traits among subspecies subtle if present (see Measurements).

Myrmeciza exsul exsul Sclater, 1859
Proceedings of the Committee of Science and Correspondence of the Zoological Society of London [“1858’], Pt. 26, No. 380, p. 540.


See Detailed Description.

Myrmeciza exsul occidentalis Cherrie, 1891
Auk 8, page 191.


Male similar to nominate exsul, but somewhat paler overall. Female upperparts similar to nominate exsul, but underparts considerably brighter than in nominate exsul. Of the female underparts Ridgway (1911) writes: "lower throat and chest bright tawny-chestnut or rufous-chestnut, passing into russet or tawny-russet on breast and abdomen, the flanks, anal region, and under tail-coverts tawny-brown (between mars brown and russet)."

This subspecies seems to differ ecologically from the nominate exsul. Observations in Carara National Park (RST) suggest that occidentalis is much more tolerant of disturbed habitat, and may either occupy much smaller territories than nominate exsul, or tolerate overlap to a much higher degree. This subspecies easily can be observed at high densities in very young secondary habitat, along forest edges, and in high light areas. This differs from nominate exsul, which occupies old secondary and primary forest (where there is little light on the forest floor), and which often occurs at lower densities, with little or no territory overlap (SW, RST, MLB, pers. obs.).

Myrmeciza exsul maculifer (Hellmayr, 1906). 
Novitates Zoologicae 13, p. 340.

Like nominate exsul, but with conspicuous white tips on greater and lesser coverts (buffy white in juvenile plumage; SW unpub. data). Underparts of female brighter than nominate exsul, as in occidentalis; i.e., "rufous chestnut" (Hilty and Brown 1986). At opposite ends of their respective ranges, both sexes of maculifer are "paler below, and less rufescent above" than cassini, but "Intergradation between these extremes is absolute" (Chapman 1917).

Myrmeciza exsul cassini (Ridgway, 1908)
Proceedings of the Biological Society of Washington 21, p. 194.

Overall similar to, but paler than, nominate exsul and niglarus (Wetmore 1972), but with conspicuous white tips on greater and lesser coverts (buffy white in juvenile plumage; SW unpub. data). Underparts of female "cinnamon orange becoming buff on breast" (Hilty and Brown 1986).

In western central Colombia, intergradation between cassini and maculifer cited by Chapman (1917), and reiterated by Todd (1927). Subspecific uncertainty of one specimen from southern Colombia noted (Bond and Meyer de Schauensee 1940).

Myrmeciza exsul niglarus Wetmore, 1962
Smithsonian Miscellaneous Collections 145, No. 1, p. 7.

Much like nominate exsul; male somewhat paler dorsally than nominate exsul (intermediate between dorsal color of nominate exsul and occidentalis; Wetmore 1972); female brighter below than nominate exsul, but not as bright as underparts of female occidentalis.

Related Species

The genus Myrmeciza has been recognized as problematic since at least the early 20th century (Todd 1927). The 20 species (Dickinson 2003, Zimmer and Isler 2003) currently placed in the genus Myrmeciza do not form a monophyletic group, with a number of species in other genera (e.g., Percnostola, Myrmoborus, Pyriglena) seemingly more closely related to various "Myrmeciza" (Irestedt et al. 2004, Brumfield et al. 2007).

The sister taxon of Myrmeciza exsul currently is unclear; no comprehensive molecular analysis currently available. Myrmeciza exsul and M. berlepschi (Stub-tailed Antbird) found to be sister taxa by Brumfield et al. (2007), and M. exsul [occidentalis + maculifer] sister to M. griseiceps (Gray-headed Antbird) by Weir et al. (2009), but neither study was intended to resolve Myrmeciza, and neither study included all putative Myrmeciza and their allies in their analyses.

Recommended Citation

Woltmann, Stefan, Ryan S. Terrill, Matthew J. Miller and Matthew L. Brady. 2010. Chestnut-backed Antbird (Poliocrania exsul), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, editor). Cornell Lab of Ornithology, Ithaca, New York, USA. https://doi.org/10.2173/nb.chbant1.01