Rio de Janeiro Antwren Myrmotherula fluminensis Scientific name definitions

This species’ status is subject to substantial conjecture. Discovered as recently as 1982, when a male was trapped and collected at an isolated woodlot near sea level in central Rio de Janeiro, the species went unrecorded again until 1994. Since then birds apparently matching the holotype of Myrmotherula fluminensis have been observed at the nearby REGUA reserve, in the same state. However, these birds are apparently vocally indistinguishable from White-flanked Antwrens (Myrmotherula axillaris luctuosa), and it seems possible, if not probable, that the Rio de Janeiro Antwren represents merely a variant plumage of the commoner species, as first suggested in 1997, or that the name fluminensis perhaps pertains to a hybrid between White-flanked Antwren and the globally threatened Unicolored Antwren (Myrmotherula unicolor). It is planned to test these hypotheses genetically, using the holotype. At present BirdLife International treats the Rio de Janeiro Antwren as a Critically Endangered species given that its known range is minuscule and is confined to the extensively deforested lowlands, although the habitat at both localities from which the species has been recorded is second growth. Rio de Janeiro seems to follow mixed-species foraging flocks, remaining low above the ground, searching for insects on branches and leaves. It has not been found above 200 m elevation.

c. 10 cm; 9 g. Male is grey, wings darker, throat and breast down to central belly black; wing-coverts black, broadly tipped white; underwing-coverts white; whitish eyering and subocular stripe. Female undescribed.

Taxonomic validity questioned by various authors; was initially thought by some to be a hybrid between M. unicolor and race luctuosa of M. axillaris, and later considered possibly a variant of latter; moreover, some uncertainty over whether recent observations refer to same taxon as original type specimen. More research, including thorough analysis of recent tape recordings, is needed in order to determine its true taxonomic status. All mentioned taxa are often grouped with M. schisticolor, M. sunensis, M. minor, M. iheringi, M. behni, M. grisea, M. snowi, M. longipennis, M. urosticta and M. menetriesii as the “grey antwren assemblage”, although this grouping possibly not monophyletic. Monotypic.

C Rio de Janeiro, in SE Brazil.

Little known. Single specimen was collected in a partially isolated and highly disturbed woodlot at c. 20 m elevation; subsequent reports from young secondary forest (up to 25 years old) adjacent to old clearings, at 35–200m.

Nothing known; specimen was obtained from a lowland site that had been studied for 7 years, prompting speculation that bird was a straggler or altitudinal migrant from slopes of nearby Serra dos Órgãos.

Almost nothing known. Stomach of sole specimen contained remains of arthropods. Mainly seen feeding in mixed-species flocks, usually within 2 m of ground.

Nothing known; recorded vocalizations purported to be of this species considered very similar, if not identical, to those of race luctuosa of M. axillaris.

Nothing known.

CRITICALLY ENDANGERED. Restricted-range species: present in Atlantic Forest Lowlands EBA. Known from a single specimen taken near Santo Aleixo, Majé in lowland Rio de Janeiro state in 1982. No further sightings from the type locality, despite subsequent fieldwork. Reported to have been rediscovered in 1994 at Guapi Açu (then Serra do Mar) Ecological Reserve, which encompasses 74 km² of privately owned land at altitudinal range of 35–2000 m; the Fazenda do Mar (20 km²) forms the core of this reserve, and adjacent landowners are expected to sign buffer-zone management agreements. Tape recordings made at Guapi Açu, alleged to be of this species, have been judged by several experienced field ornithologists to be very similar, even identical, to vocalizations of M. axillaris of race luctuosa, leading to published speculation that the Guapi Açu birds represent a local variant of that taxon; thorough analysis of tape-recorded vocalizations of the Guapi Açu individuals is required in order to determine if they are diagnosably different from luctuosa. Additional research needed to establish if these birds represent the same taxon as the type specimen. Further surveys at Guapi Açu in 2003–2004 failed to find the species (1 Pimentel, L., and F. Olmos (2011). The birds of Reserva Ecológica Guapiaçu (REGUA), Rio de Janeiro, Brazil. Cotinga 33:6–22. Close ). There is a pressing need for surveys to locate any additional sites for this antwren and obtain information on its ecology and conservation requirements. If it is, in fact, a forest bird, then habitat loss in this highly deforested region of Brazil is likely to be the most critical conservation issue. Considered Critically Endangered (Possibly Extinct) at the national level in Brazil (2 MMA (2014). Lista Nacional Oficial de Espécies da Fauna Ameaçadas de Extinção. Portaria No 444, de 17 de dezembro de 2014. Diário Oficial da União - Seção 1. Nº 245, quinta-feira, 18 de dezembro de 2014. Close ).