Cordillera Azul Antbird Myrmoderus eowilsoni Scientific name definitions

One of the most remarkable ornithological discoveries of 2016 was that of a new population of Myrmoderus antbird in the Cordillera Azul of north-central Peru. These birds most closely resemble Ferruginous-backed Antbird (M. ferrugineus) of the Guianan region and central Amazonian Brazil, but differ in plumage and song. As a result, this antbird was described as a separate species, Cordillera Azul Antbird. Both sexes are rufous above, with bare bluish orbital skin, and a moderately long tail; the wing-coverts are black, tipped buff. The male has black ear-coverts, neck-sides , and underparts; and the female also has black ear-coverts, but the throat is white, the breast is rufous, and the belly is dark brown. Currently Cordillera Azul Antbird is known only from two localities in close proximity to one another, but presumably it is more widely distributed within the Cordillera Azul. This antbird is terrestrial, and apparently occurs only within tall, evergreen, lower montane forest, and usually is encountered in pairs. Otherwise very little is known about the biology of the striking antbird.

The only Thamnophilidae in range that has a combination of black ear-coverts, mainly rufous-brown upperparts, blackish wing-coverts with broad white or buff tips, bluish bare orbital skin, gray feet and tarsi, no obvious white interscapular patch, and terrestrial walking behavior.

Cordillera Azul Antbird is most similar to the allopatric Ferruginous-backed Antbird (M. ferrugineus), but differs in having a colder brown crown and nape, a gray rather than white supercilium, less extensive bluish bare orbital skin, and black (male) or dark brown (female) belly, whereas both sexes of Ferruginous-backed Antbird show substantial white in this area. Furthermore, female Cordillera Azul Antbird has a rufous breast, whereas female Ferruginous-backed Antbird has a black breast. In addition, their songs differ, with Cordillera Azul Antbird having fewer notes and is slower paced.

Nestling

Undescribed.

Juvenile

Like adult, but a young female had a nearly pure white throat and chin, with greatly reduced scaling (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ).

Adult

Male. Description based on that of the holotype (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ). Crown and nape warm sepia-brown, with feather tips edged slightly darker, producing a faintly scaled appearance. Forehead and lores black. Supercilium pale gray, beginning above anterior edge of eye, extending to and broadening at nape. Back brown, becoming brighter on upper scapulars and upper mantle, with a rudimentary white interscapular patch. Rump and uppertail-coverts brown. Uppertail brown, tending toward fuscous-black, with uniform fuscous underside. Lesser coverts black with narrow white tips, becoming entirely white on leading edge of wing. Greater and median coverts black, broadly tipped warm buff to ochraceous-buff, but sometimes white, forming two obvious wingbars. Primary-coverts black, narrowly tipped warm buff. Primaries and secondaries fuscous-black with brown fringes, tertials fuscous with diffuse black subterminal spot on ss7–8, and diffuse cinnamon tips on outer vanes. Chin, throat, ear-coverts, breast, sides, upper flanks, and belly black, grading to umber on vent and lower flanks. Undertail-coverts brown. Underwing-coverts blackish, with the greater coverts tipped white.

Female. Differs from the adult male in having the throat and malar white with fine black tips, becoming more extensively black toward chin; breast and sides between orange and amber-brown; and central belly dark gray, becoming umber on the surrounding belly and the flanks and vent.

No information (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ).

The only data pertain to the adult male holotype (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ).

Bill

Mandible blue-gray, and maxilla blackish with blue-gray tomium.

Iris

Dark brown, with blue-gray orbital skin.

Legs and Feet

Dark gray.

Linear Measurements

Overall length c. 14–15 cm.

Linear measurements (in mm, with means plus standard deviation for sexes combined, and sample sizes in parentheses, from Moncrieff et al. 1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ):

Mass

24.7–29.0 g (27.4 ± 2.6; n = 8) (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ).

A recently described species that is most closely related to Ferruginous-backed Antbird (M. ferrugineus) (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ).

None known.

M. eowilsoni was recovered as sister to Ferruginous-backed Antbird (M. ferrugineus) with high support in all genetic analyses performed to date (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ).

This species is named in honor of E. O. Wilson “to recognize his tremendous devotion to conservation and his patronage of the Rainforest Trust, which strives to protect the most imperiled species and habitats in the Neotropics and across the globe” (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ).

Nothing known.

Confined to northern Peru, where it is apparently found only on ridge crests in the Cordillera Azul (eastern San Martín) (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ).

None known.

Apparently restricted to tall, montane, evergreen forest with intact understory characterized by small trees (diameter at breast height c. 5–10 cm) and ferns, many moss-covered logs, and extensive dead leaf matter on the ground, usually on or near level ridgetops, at 1,340–1,670 m (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ).

Presumably resident and sedentary.

This species is observed only within 1 m of the ground, typically moving by short, low flights, and by walking slowly along the ground. Birds pick through the leaf litter searching for arthropod prey, which have also been found in stomach contents of specimens (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ). Diet and foraging behavior are presumably very similar to Ferruginous-backed Antbird (M. ferrugineus).

The following is based on Moncrieff et al. (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ). Songs of both sexes are characterized by having a clear whistled quality, rather few notes, and a simple pattern. Males give four whistled notes in two couplets (songs of 2–3 notes heard rarely), usually with the first note highest in pitch, the second lower, the third of similar or slightly higher pitch, and the final note lowest in pitch. Male song is quite stereotyped, but with minor variation, especially in pitch. Compared to the song of M. ferrugineus, it comprises fewer notes (2–6 versus 8–14) delivered more slowly (mean c. 2 notes/second versus c. 7 notes/second), and can be likened to the slowed-down terminal two couplets of male M. ferrugineus. Like M. ferrugineus, the songs of the present species are sexually dimorphic (i.e. female songs differ consistently from those of males in pattern, note number, and note shape). The song of female M. eowilsoni exhibits broader variation within and among individuals in pitch and number of notes (3–6) than males, and is delivered more slowly, often with a raspier quality. The call consists of a sputtering series of notes similar to the call of M. ferrugineus, but is slower, and occasionally consists of only single or doubled notes.

Virtually nothing known. A female collected in July had slightly enlarged ovaries (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ).

Maximum territory size estimated at 0.25 km² (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ).

Not globally threatened. Currently considered Near Threatened. Population believed to be declining and is estimated at 7,000–34,000 individuals within an overall range of perhaps 34,500 km^². Based on the maximum territory size of M. eowilsoni and the mean territory size of Ferruginous-backed Antbird (M. ferrugineus) (2 Johnson, E. I., P. C. Stouffer, and C. F. Vargas (2011). Diversity, biomass, and trophic structure of a central Amazonian rainforest bird community. Revista Brasileira de Ornitologia 19(1):1–16. Close ), as well as an estimate of habitat occupancy for the latter species (3 Stouffer, P. C. (2007). Density, territory size, and long-term spatial dynamics of a guild of terrestrial insectivorous birds near Manaus, Brazil. Auk 124(1): 291–306. Close ), and the projected availability of suitable habitat for the present species, Moncrieff et al. (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ) suggested that because Cordillera Azul National Park supports 1,940 km^² of forest at 1,300–1,700 m, the population of M. eowilsoni therein could comprise between 7,000 and 27,000 mature individuals. However, to date the species has not been found in the national park, but because most of the estimated range of M. eowilsoni lies inside this protected area, and it might even extend even further south, to the Cordillera El Sira (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ), Cordillera Azul Antbird is not believed to be at risk due to extensive habitat loss. Nevertheless, habitat alteration, primarily clear-cutting, is extensive and ongoing around the type locality (which lies outside the national park), and much of the remaining forest there may soon be lost (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ). Consequently, survey work is urgently needed to determine the full distribution of M. eowilsoni, to assess territory size and occupancy, and to improve estimates of population size (1 Moncrieff, A. E., O. Johnson, D. F. Lane, J. R. Beck, F. Angulo, and J. Fagan (2018). A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. Auk 135(1):114–126. Close ).

Guy Kirwan grew up in northwest England, close to the one of the world’s largest Larus colonies, and has been interested in birds since the late 1970s. Following a three-year period in the early 1990s working in Turkey for the then BirdLife International International partner, mainly on threatened waterfowl and wetland conservation, which ultimately led to the standard monograph on the country’s birds (Kirwan et al. 2008), his attentions turned primarily to the Neotropics, and the Western Hemisphere in general. He has spent well over 12 years in the field in this region, from Alaska in the extreme north, to Tierra del Fuego in the far south, with special foci on the birds of Brazil and Cuba. Between 1999 and 2010, he was semi-resident in Brazil. Lead author of Cotingas and Manakins (Kirwan & Green 2011), the now-standard work to these perennial favourites among Neotropical birders, and a new field guide to the Birds of the West Indies (Kirwan et al. 2019), he is currently finalizing a detailed checklist to Cuban birds (Kirkconnell et al. in prep.) which should be published in 2020. A freelance ornithologist and editor, notably of the Bulletin of the British Ornithologists’ Club (since 2004), but also more than 40 books (among them recent titles such as Wildfowl of Europe, Asia and North America by Sébastien Reeber, and the two-volume Handbook of Western Palearctic Birds: Passerines by Hadoram Shirihai & Lars Svensson), his main research interests are in avian taxonomy and the breeding biology of passerines in the New World tropics. To date, Guy has authored more than 150 papers in the technical literature, including the descriptions of three new species, three subspecies and two genera. A Research Associate at the Field Museum of Natural History in Chicago, and the Museu Nacional in Rio de Janeiro, he was a member of the now disbanded British Ornithologists’ Union’s Taxonomic Subcommittee, and until recently sat on the board of the Trust for Avian Systematics.