Marsh Antwren Formicivora paludicola


Justification of Red List Category
This newly described species is immediately considered to be Critically Endangered, due to the tiny overall area of occupancy and fragmented nature of the population as demonstrated by genetic investigation coupled with the declining suitability of the habitat due to human development and vegetative changes caused by an invasive grass species.

Population justification
The population was initially estimated at between 250 and 300 individuals, but genetic analysis demonstrated an effective population size of approximately 50 birds in each of the three largest populations, estimated to represent a census size of between 220-582 individuals within approximately 60% of the total area of marsh habitat within the sites that the species has been recorded (Camargo et al. 2015). Accordingly the population of the species can be placed with good confidence in the band 250-1,000 individuals, roughly equivalent to 166-667 mature individuals which is rounded here to 150-700 mature individuals.The genetic structure of the subpopulations has been investigated and suggests that even though the species is highly restricted in range, there is a considerable degree of genetic differentiation between the three sites holding the largest number of individuals, indicating a minimum of three subpopulations within the species (Camargo et al. 2015). This concerning finding indicates that the species can be considered to be severely fragmented, with each subpopulation at risk of extinction with limited possibility of recolonization.

Trend justification
Two of the sites at which the species has been recorded have been lost subsequent to their discovery. 72 individuals were captured and translocated from one of these sites to 10 surrounding marshes of which 7 appeared to be new sites. Therefore, despite the loss of two sites, the population trend is not suspected to be decreasing as birds have begun breeding at the new sites. Therefore the population trend is uncertain.

Distribution and population

Formicovora paludicola was discovered only in October 2004 and is known from a very restricted area in the headwaters of the Tietê and Paraíba do Sul river basins, Sao Paulo state, Brazil (Buzzetti et al. 2013, Kirwan 2016). Following the discovery of F. paludicola, exhaustive searches at more than 50 sites revealed its presence in a total of 15 small marshes, all less than 45 ha (Buzzetti et al.2013). Two of these sites have subsequently been lost, one to the construction of a dam from where 72 individuals were captured and translocated to 10 surrounding marshes, 7 of which appear to be sites that previously did not hold the species (Buzzetti et al. 2013, Camargo et al. 2015). Subsequently these translocated birds have persisted and been reported to have successfully bred (Buzzetti et al. 2013). The small size and discrete nature of these sites indicate that it is safe to assume that the area of occupancy for the species falls below 10 km2.


The habitat of the species is small bulrush and cattail marshes, is under threat from sand mining activity and other developments such as for housing or fish farming. Additionally the invasion of the marsh by the introduced grass Urochloa arrecta appears to render the marshes unsuitable for the species, and is a considerable threat (Buzzetti et al. 2013).


Current threats come from anything affecting the tiny patchwork of marshes that form the entire range of the species. In particular sand mining activity and other developments such as for housing or fish farming have been identified (Buzzetti et al. 2013). The invasion of marshes in the species range by the introduced grass Urochloa arrecta appears to render the marshes unsuitable for the species, and is a considerable threat (Buzzetti et al. 2013).

Conservation actions

Conservation Actions Underway
Officially recognised as Critically Endangered in Brazil (MMA 2014). 

Conservation Actions Proposed
Protect key sites, and prevent further development projects affecting the marshes in which the species occurs. Investigate the impact of the invasive grass Urochloa arrecta on populations and the potential for its spread to further sites.


Text account compilers
Martin, R, Westrip, J.

Lebbin, D.

Recommended citation
BirdLife International (2018) Species factsheet: Formicivora paludicola. Downloaded from on 20/01/2018. Recommended citation for factsheets for more than one species: BirdLife International (2018) IUCN Red List for birds. Downloaded from on 20/01/2018.