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Myrmotherula assimilis

Leaden Antwren

  • Order: Passeriformes
  • Family: Thamnophilidae
  • Polytypic 2 Subspecies

Authors: Schulenberg, Thomas S., and Gary H. Rosenberg

Identification

Summary

Myrmotherula antwrens are very small thamnophilids. The Leaden Antwren is a member of the group of "gray antwrens", the males of which are predominately gray and the females are predominately buffy brown. The male Leaden is a pale gray antwren with white wingbars; the female is plain, gray above and buff below with weak buff wingbars. 

Similar Species

Male Leaden Antwren is closely similar to male of the northern subspecies (pallida) of Gray Antwren (Myrmotherula menetriesii), but there is no overlap in habitat: Leaden Antwren is restricted to forests on large river islands and is not found on the adjacent river banks. Also, male Leaden Antwren has plainer wing coverts (lacking the gray, black and white pattern of male Gray Antwren), and has a white interscapular patch (lacking in Gray). Female Leaden Antwren separable from similar species by habitat, by the white interscapular patch, and by the much stronger, whiter wingbars.

Vocalizations

The song of the Leaden Antwren is "an accelerating, descending trill: tew tew-tew-tew'tew'tew'tew'tu'tu'teerrrrrrrru" (Lane, in Schulenberg et al. 2007). Call "a short, downslurred snew, emphatic and somewhat harsh" (Zimmer and Isler 2003).

Nonvocal Sounds

None reported.

Detailed Description (appearance)

Adult, male: Crown, back and rump medium gray; bases of feathers in the center of the back white, forming a concealed white interscapular patch. Remiges dusky. Wing coverts medium gray, tipped white. Tail gray; usually unmarked, but rarely the undersides of the outermost rectrices narrowly are tipped white. Underparts pale gray, palest on the throat.

Adult, female: Crown, back and rump medium brownish gray or olive gray. Bases of feathers in the center of the back white, forming a concealed white interscapular patch. Remiges olive brown. Wing coverts olive brown, narrowly tipped pale buff or whitish buff. Tail gray or dusky. Sides of the face and neck pale gray. Throat whitish buff. Breast and belly pale buff.

Bare Parts

Iris: brown

Bill: black (males) or maxilla black, mandible gray (females)

Tarsi and toes: blue-gray

Data from specimens at the Louisiana State University Museum of Natural Science.

Measurements

Total length: 9-10 cm (Zimmer and Isler 2003), 9.5-10 cm (Ridgely and Tudor 2009), 10 cm (Schulenberg et al. 2007)

Linear measurements:

 

Linear measurements (mm) of Myrmotherula assimilis (Gyldenstolpe 1951)
     wing tail  culmen
            assimilis    
  male   mean     52.3   28.0   12.8
  range (n = 26)
  51-54  27-29  12-14
  female mean     52.0   28.2    12.9
  range (n = 15)   50-55  27-30   12-14
             transamazonica   
  male mean    56.8    29.8    14.3
  range (n = 6)   56-58   28-31   14-15
  female  mean    55.9    30.3     14
   range (n = 7)   54-57   30-31    14-14

 

Mass: male, 9.3 g (range 8.4-10.5 g, n=13); mean female, mean 9.3 g (range 8.2-10.5, n=12). Data from specimens at the Louisiana State University Museum of Natural Science.

Molts

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Geographic Variation

Two subspecies recognized:

assimilis Pelzeln 1869; type locality Borba; Pojares, Rio Negro, and Rio Amajau, Rio Negro.

The nominate subspecies occupies most of the range of the species.

transamazonica Gyldenstolpe 1951; type locality Urucurituba, Rio Amazon (opposite Santarém), Pará, Brazil

Found along the Amazon near the Rio Tapajos, Brazil. "Distinguished by its larger dimensions, the wings being particularly longer and the bill somewhat longer and heavier, as well as broader at the base ... The gray color of the dorsal parts is lighter than that of the nominate form. The females have also a distinct white, concealed white interscapular patch, and the dimensions also are larger than those of M. a. assimilis" (Gyldenstlope 1951: 198).

Systematics

The phylogenetic relationships of Myrmotherula assimilis to other species are poorly known. Implicitly classified as related to other "gray antwrens" in Myrmotherula. Limited genetic evidence (from protein electrophoresis) indicates that assimilis is not a Myrmotherula at all, however, but instead is a member of a clade that also includes Thamnophilus (antshrikes), Dysithamnus (antvireos), and Herpsilochmus (antwrens) (Hackett and Rosenberg 1990).

Recommended Citation

Schulenberg, Thomas S., and Gary H. Rosenberg. 2011. Leaden Antwren (Myrmotherula assimilis), Neotropical Birds Online (T. S. Schulenberg, Editor). Ithaca: Cornell Lab of Ornithology; retrieved from Neotropical Birds Online: http://neotropical.birds.cornell.edu/portal/species/overview?p_p_spp=379091