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 where 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 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 seven 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. 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, Del-Rio et al. 2015, 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, seven of which appear to be sites that previously did not hold the species (Buzzetti et al. 2013, Camargo et al. 2015). The 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, where it occurs at densities of around 3.6 mature individuals/ha. The species's habitat is under severe 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 and ginger lily Hedychium coronarium appears to render the marshes unsuitable for the species, and represents a considerable threat (Buzzetti et al. 2013, Del-Rio et al. 2017).


Current threats arise from anything affecting the tiny patchwork of marshes that form the entire range of the species. Within the last 100 years, the marshlands around Sao Paulo have been almost completely lost (Del-Rio et al. 2015). In particular, sand mining activity, agriculture 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 two invasive plants, the grass Urochloa arrecta and the ginger lilly Hedychium coronarium, appears to render the marshes unsuitable for the species, and is a considerable threat (Buzzetti et al. 2013, Del-Rio et al. 2017).

Conservation actions

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

Conservation Actions Proposed
Protect key sites, especially older marshes with a high plant biodiversity, and prevent further development projects affecting the marshes in which the species occurs. Restore marshland in the Rio Tietê and Rio Paraíba do Sul basins. Enhance connectivity between patches occupied by the species. Investigate the impact of the invasive grass Urochloa arrecta and ginger lily Hedychium coronarium on populations and their potential spread to further sites.


Text account compilers
Hermes, C., Martin, R., Westrip, J.

Lebbin, D.

Recommended citation
BirdLife International (2023) Species factsheet: Formicivora paludicola. Downloaded from on 29/11/2023.
Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from on 29/11/2023.