Justification of Red List Category
This species is has a very small range, within which its habitat is inferred to be declining in quality and extent through clearance for development and agriculture. Over 90% of the population is thought to be restricted to one subpopulation, so the population could be severely reduced by a very small number of development projects. For these reasons, the species is listed as Endangered.
This species has an extremely small range, and it has been reported to be difficult to locate (Tobias et al. 1993, Tobias and Williams 1996), although it is considered locally abundant in suitable habitat (CEMAVE 2018). Reported densities are 156 pairs/km2 at Vale do Mambucaba and 89 pairs/km2 at Ariró (Gonzaga 2008), which collectively are thought to hold more than 90% of the total population (CEMAVE 2018). Although the population size has not been directly quantified, it is suspected to be smaller than 250 mature individuals, based on sightings by researchers within the range (CEMAVE 2018).
Based on an assumed minimum population density of 40 individuals/km2 (consistent with status as a locally common antwren), an upper density of 267 individuals/km2 (assumed equivalent to 89 pairs/km2), and assuming 11-45% of the mapped range is occupied, the population is here suspected to number 475-12,680 individuals . This equates to approximately 317-8,453 mature individuals, here rounded to 300-8,500 mature individuals. The population size is therefore placed in the band 50-8,500 mature individuals.
The number of subpopulations is not known. Based on discontinuities between areas with records, the species is assumed to have at least two subpopulations. According to the Brazilian national Red List, 90-100% of individuals are thought to comprise a single subpopulation (CEMAVE 2018). The largest subpopulation is therefore suspected to hold 45-8,500 mature individuals.
An ongoing slow population decline is suspected to be taking place, based on observational information (Tobias and Williams 1996) and remote-sensed data (Global Forest Watch 2020) on habitat loss. From 2010 to 2019, approximately 4% of tree cover was lost within the species's range (Global Forest Watch 2020). The species is tolerant of degraded habitat and occurs in scrubby habitats and secondary forest, so there is a low level of confidence in the population trend, but the species is suspected to be declining, with a suspected population reduction over the last ten years of 1-4%. In 2017, approximately 0.8% of forest within the species's range was lost within a single year (Global Forest Watch 2020). Extrapolating this rate over 10 years would equate to approximately 8%. Using this value as a maximum, the population is suspected to decline by 1-8% over the next decade.
Formicivora erythronotos is found in a narrow coastal strip around the Ilha Grande bay in south Rio de Janeiro state, Brazil. Although known from c.20 specimens collected in the 19th century, it was unrecorded for over 100 years until its rediscovery in 1987 in the Angra dos Reis area of the Ribeira bay. It has now been recorded at a total of seven sites along the bay of Ilha Grande and in Serra do Piloto (Gonzaga 2008), within the municipalities of Angra dos Reis and Paraty (Buzzetti 1998, E. Mendonça and L. P. Gonzaga in litt. 2000): Ariró, Vale do Mambucaba, Bracuí, Frade, São Gonçalo, Taquari and Barra Grande (Buzzetti 1998, Mendonça and Gonzaga 1999b, E. Mendonça and L. P. Gonzaga in litt. 2000).
It was rediscovered in a swampy patch of secondary forest near the forest-mangrove ecotone. Subsequent records have found the species to occur mostly in the lush understorey of modified restinga, early successional habitats such as the understorey of old second growth (Mendonça and Gonzaga 1998, Mendonça and Gonzaga 1999b), and sometimes abandoned banana plantations reverting to secondary forest (E. Mendonça and L. P. Gonzaga in litt. 2000). These areas are dominated by pioneer species, including Lantana camara, Cecropia sp., Morus sp., Rubus, Vernonia sp. and grasses (Mendonça and Gonzaga 1999b). It has once successfully colonised fields two months after burning, where there was little regenerating vegetation (Mendonça and Gonzaga 1999a,b). Nests have been found in second growth from mid-August to early February, with eggs producing an average of 0.23 young (Mendonça and Gonzaga 1999a).
Development of the narrow coastal plain for tourism and beachside housing has been extensive and threatens the small remnant patches of suitable habitat (Tobias et al. 1993, Tobias and Williams 1996). There is widespread clearance of Euterpe sp. palms for pasture and plantations, both of which provide unsuitable habitat for this species (Mendonça and Gonzaga 1999b). Such plantations have reduced available habitat in the Vale do Mambucaba (E. Mendonça and L. P. Gonzaga in litt. 2000).
Conservation Actions Underway
It is protected under Brazilian law and occurs in the buffer-zone of the Serra da Bocaína National Park and in the Tamoios ecological station. Formerly considered Endangered at the national level (Silveira and Straube 2008), it is now designated as Critically Endangered under Brazilian law (MMA 2014) and is included in the National Action Plan for the Conservation of the Birds of the Atlantic Forest (ICMBio 2017).
11.5 cm. Distinctive, black-and-rufous antwren. Male slaty-black with rufous-chestnut back. Black wings with three narrow, whitish wing-bars. White flanks often concealed. Slender black bill. Female similar to male but slaty-black replaced by olivaceous-brown, becoming more buffy on underparts. Voice Song is three-second series of low-pitched tchóup calls. Also high-pitched tcheek calls and soft churrs.
Text account compilers
Clay, R.P., Gonzaga, M., Mendonça, E., Pople, R., Sharpe, C.J., Symes, A. & Williams, R.
BirdLife International (2022) Species factsheet: Formicivora erythronotos. Downloaded from http://www.birdlife.org on 07/10/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 07/10/2022.