5 thoughts on “Dot-winged Crake (Laterallus spilopterus)”
The proposal to downlist the Dot-winged Crake rests on new vocalization data that, while expanding its known range, do not provide sufficient evidence of a demographically continuous or connected population. Although the population is now estimated between 10,000 and 19,000 mature individuals, with declines of 1–19% over the past decade, the evidence strongly supports retaining the Vulnerable status under criterion C2a(i). Specifically, I note the following:
Population Structure and Subpopulation Connectivity:
Although rails are known for wide-ranging dispersal, such movements do not necessarily result in gene flow or stable demographic connectivity. Apart from coastal Chile, and Andean and pre-Cordileraan areas of Argentina, most new records are of isolated individuals or vagrants, not established breeding subpopulations. Data suggests that the species is largely restricted to discrete saltmarsh patches along Atlantic and Pacific estuaries or in a few inland wetlands within or near brackish areas. Consequently, the assumption of a single, continuous subpopulation is unwarranted, reinforcing the VU assessment under C2a(I).
Extent of Occurrence and Habitat Specificity:
The currently used maps, from BirdLife International’s DataZone, Cornell’s Birds of the World, and Ruiz et al. (2003), overestimate the Extent of Occurrence (EOO), presently estimated at 2,103,000 km², by including vast areas of unsuitable habitat (e.g., grasslands, croplands, sand dunes and freshwater marshes), particularly in Brazil and Uruguay. A more realistic assessment would target areas with saline soils and halophytic vegetation, revealing a fragmented distribution confined to saltmarshes and tracts of inland wetlands, mostly in brackish conditions. In Brazil, for example, the species is confirmed only from three coastal sites (near Laguna in Santa Catarina, and at Lagoa do Peixe and the Lagoa dos Patos estuary in Rio Grande do Sul), and similarly, records in Uruguay are limited to a few coastal lagoons. This species is not expected to have a distribution such as the Rufous-sided Crake (Laterallus melanophaius), as seen in the eBird species map, which occurs mainly in freshwater marshes in the region.
Dispersal, Disturbance, and Demographic Viability:
Although dispersal is a characteristic behavior among rails, such movements typically lead to mortality and may result from ecological disturbances like fluctuations in water levels and fires. Megafires recorded in Argentina and megafloods, such as the extreme event in 2024 that flooded the Lagoa dos Patos estuary, demonstrate that these disturbances can degrade otherwise high-quality habitat. As a result, these events may induce temporary declines in mature individuals without necessarily ensuring long-term population connectivity. The effective gene flow among these isolated subpopulations is thus highly uncertain.
Habitat Threats and Ongoing Pressures:
While coastal saltmarshes in Brazil, Uruguay, and Argentina are not experiencing rapid conversion, they remain under severe threat from climate change. Rising sea levels present a long-term risk, and habitat quality is further compromised by cattle trampling, overgrazing, and episodic disturbances. Even in regions where habitat reduction appears stable (e.g., the lower Paraná Delta from 2012–2023), marshes around Buenos Aires have undergone conversion due to urban sprawl (see MapBiomas data), illustrating the broader pressures on these wetlands. Such threats, along with extreme weather events and fire, underscore that habitat modification may be a more significant concern than outright habitat loss.
Synthesis and Conservation Implication:
I acknowledge that there is no evidence of extirpation from any portion of the species’ range and that the overall population figures may seem moderately stable. However, the new data do not support the hypothesis that the species exists as a single, cohesive unit. Instead, evidence suggests that L. spilopterus is confined to isolated, disturbance-prone patches of saltmarsh habitat, wherein demographic connectivity is unlikely despite occasional long-distance movements typical of rails. Until thorough population-level studies confirm stable or increasing trends across these fragmented areas, and until habitat suitability models based on saline conditions are developed, the precautionary approach dictates that the Vulnerable status under C2a(i) remains justified.
Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested in commenting. The window for consultation is now closed and we are unable to accept any more comments until 25 April 2025. We will now analyse and interpret the information, and we will post a preliminary decision on this species’ Red List category on this page on 25 April 2025, when discussions will re-open.
Based on available information, our preliminary proposal for the 2025 Red List would be to list
Dot-winged Crake as Near Threatened under Criterion C2a(ii).
Many thanks to Rafael Antunes Dias for this detailed and considered reply.
A technical point on EOO: this is a minimum convex polygon around the known range, including all the area this encompasses whether suitable or not. It is intended to address the spatial distribution of threats affecting the extinction risk of the species, not to measure the area the species occupies, which is achieved through the Area of Occupancy (AOO). With confirmed breeding in Chile and southern Brazil, this species cannot approach Red List thresholds for EOO. Deriving an AOO value requires an assessment of presence and absence across the range, which is challenging for this species given the recent improvement in detection after the call became known, and uncertainty over movements.
To assess the species as Vulnerable under C2a(i) requires meeting three subcriteria:
1, the population size must be estimated at under 10,000 mature individuals
2, there must be an inferred, estimated or observed continuing decline in the population size,
3, the largest subpopulation must contain fewer than 1,000 mature individuals.
The population size for the proposed reassessment here is inferred, not estimated. As noted, the recent expansion of the range enabled by the new understanding of the vocalisations indicates that the population size is likely to be much larger than previously thought. The previous estimate of 2,500-9,999 was based on the distribution being restricted to those few coastal, saltmarsh sites in southern Brazil, Uruguay and Argentina. Many calling birds have been located where habitat has been visited with knowledge of the call: many additional sites exist that are yet to be visited by those that know the call. That supplies uncertainty but allows the inference that the overall population size is larger than previously thought.
The point made on the potential for large-scale but short-term habitat change due to fire or flood causing novel dispersal records is worth consideration. The pattern of records suggests movement is a regular habit of the species, rather than occurring in response to one-off events. Notably all records at the southern edge of the range fall between October and March, while extralimital vagrants to the north of the mapped range occur in April and May: a typical pattern for dispersing individuals in the post-breeding period. The breeding record in Chile falls in the first period, and there are numerous records of birds calling in suitable breeding habitat in this part of the range at this time of the year. Records occur year-round in Buenos Aires and Cordoba provinces, Uruguay and Brazil, and the more northerly parts of Chile. This could be explained if part of the population makes seasonal movements to access ephemeral resources. This may imply a smaller overall population size if habitat in part of the range is used seasonally, introducing further uncertainty as we cannot use the total area of habitat to approximate population size.
Alternatively, there may be a bias in search effort in the south of the range such that birds are only detected in the Austral summer, when they are present year-round. This seems unlikely, given that there is some observer effort in these areas year-round, and as noted there are records through the year further north. The IUCN criteria weights single populations more highly than multiple subpopulations, unless these really are very small. Faced with evidence that the population is not very small, it is more precautionary to assume a single population when applying Criterion C.
Given the observation that no known occupied sites appear to have lost the species, despite some being very small, and that there are records in novel wetland habitats indicating that the species can discover these sites, and that vagrant individuals have been found up to several hundred kilometres from the expected range, it is concluded the species is capable of long-range dispersal and that individuals make movements on a regular basis.
Based on the greater specialisation on saline marshes, correctly pointed out by Rafael Antunes Dias, it is plausible that the population is still small and is inferred to be declining due to habitat loss and degradation. Our preliminary proposal for the 2025 Red List would be to list Dot-winged Crake as Near Threatened, approaching thresholds under Criterion C2a(ii).
There is now a period for further comments until the final deadline on 4 May 2025, after which the recommended categorisations will be put forward to IUCN.
The final 2025 Red List categories will be published on the BirdLife and IUCN websites in October 2025, following further checking of information relevant to the assessments by both BirdLife and IUCN.
Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested in commenting. The window for consultation is now closed and we are unable to accept any more comments. We will analyse and interpret the information, and a final decision on this species’ Red List category will be posted on this page on 12 May 2025.
Recommended categorisation to be put forward to IUCN
The final categorisation for this species has not changed. Dot-winged Crake is recommended to be listed as Near Threatened, approaching thresholds under Criterion C2a(ii).
Many thanks for everyone who contributed to the 2025.2 GTB Forum process. The final Red List categories will be published on the BirdLife and IUCN websites in October 2025, following further checking of information relevant to the assessments by both BirdLife and IUCN.
The proposal to downlist the Dot-winged Crake rests on new vocalization data that, while expanding its known range, do not provide sufficient evidence of a demographically continuous or connected population. Although the population is now estimated between 10,000 and 19,000 mature individuals, with declines of 1–19% over the past decade, the evidence strongly supports retaining the Vulnerable status under criterion C2a(i). Specifically, I note the following:
Population Structure and Subpopulation Connectivity:
Although rails are known for wide-ranging dispersal, such movements do not necessarily result in gene flow or stable demographic connectivity. Apart from coastal Chile, and Andean and pre-Cordileraan areas of Argentina, most new records are of isolated individuals or vagrants, not established breeding subpopulations. Data suggests that the species is largely restricted to discrete saltmarsh patches along Atlantic and Pacific estuaries or in a few inland wetlands within or near brackish areas. Consequently, the assumption of a single, continuous subpopulation is unwarranted, reinforcing the VU assessment under C2a(I).
Extent of Occurrence and Habitat Specificity:
The currently used maps, from BirdLife International’s DataZone, Cornell’s Birds of the World, and Ruiz et al. (2003), overestimate the Extent of Occurrence (EOO), presently estimated at 2,103,000 km², by including vast areas of unsuitable habitat (e.g., grasslands, croplands, sand dunes and freshwater marshes), particularly in Brazil and Uruguay. A more realistic assessment would target areas with saline soils and halophytic vegetation, revealing a fragmented distribution confined to saltmarshes and tracts of inland wetlands, mostly in brackish conditions. In Brazil, for example, the species is confirmed only from three coastal sites (near Laguna in Santa Catarina, and at Lagoa do Peixe and the Lagoa dos Patos estuary in Rio Grande do Sul), and similarly, records in Uruguay are limited to a few coastal lagoons. This species is not expected to have a distribution such as the Rufous-sided Crake (Laterallus melanophaius), as seen in the eBird species map, which occurs mainly in freshwater marshes in the region.
Dispersal, Disturbance, and Demographic Viability:
Although dispersal is a characteristic behavior among rails, such movements typically lead to mortality and may result from ecological disturbances like fluctuations in water levels and fires. Megafires recorded in Argentina and megafloods, such as the extreme event in 2024 that flooded the Lagoa dos Patos estuary, demonstrate that these disturbances can degrade otherwise high-quality habitat. As a result, these events may induce temporary declines in mature individuals without necessarily ensuring long-term population connectivity. The effective gene flow among these isolated subpopulations is thus highly uncertain.
Habitat Threats and Ongoing Pressures:
While coastal saltmarshes in Brazil, Uruguay, and Argentina are not experiencing rapid conversion, they remain under severe threat from climate change. Rising sea levels present a long-term risk, and habitat quality is further compromised by cattle trampling, overgrazing, and episodic disturbances. Even in regions where habitat reduction appears stable (e.g., the lower Paraná Delta from 2012–2023), marshes around Buenos Aires have undergone conversion due to urban sprawl (see MapBiomas data), illustrating the broader pressures on these wetlands. Such threats, along with extreme weather events and fire, underscore that habitat modification may be a more significant concern than outright habitat loss.
Synthesis and Conservation Implication:
I acknowledge that there is no evidence of extirpation from any portion of the species’ range and that the overall population figures may seem moderately stable. However, the new data do not support the hypothesis that the species exists as a single, cohesive unit. Instead, evidence suggests that L. spilopterus is confined to isolated, disturbance-prone patches of saltmarsh habitat, wherein demographic connectivity is unlikely despite occasional long-distance movements typical of rails. Until thorough population-level studies confirm stable or increasing trends across these fragmented areas, and until habitat suitability models based on saline conditions are developed, the precautionary approach dictates that the Vulnerable status under C2a(i) remains justified.
Literature:
BirdLife International DataZone. (2025). DataZone [Website]. Retrieved [2025], from http://datazone.birdlife.org
Chatellenaz, M. L., & Zaninovich, S. C. (2009). Primer registro de Porzana spiloptera (Aves, Rallidae) en el nordeste argentino. FACENA, 25, 49–53.
Cornell Laboratory of Ornithology. (2025). Birds of the World [Website]. Retrieved [2025], from https://birdsoftheworld.org
Dias, R. A. (2018). Porzana spiloptera Durnford, 1877. In ICMBio (Ed.), Livro vermelho da fauna brasileira ameaçada de extinção: Volume III – Aves (pp. 136–138). Brasília, DF: ICMBio/MMA.
Fariña, N., Cardinale, L., & Villalba, O. (2021). Aportes al conocimiento del burrito negruzco (Porzana spiloptera) en la Provincia de Corrientes, Argentina. Nuestras Aves, 66, 23–26.
Larracoechea, G. A. (2017). Nidificación del Burrito Negruzco (Porzana spiloptera) en Villa del Mar, Buenos Aires, Argentina. Nuestras Aves, 62, 24–27.
Lucero, F. (2013). Primer registro documentado confirmando la presencia del Burrito Negruzco (Porzana spiloptera) para la provincia de San Juan, Argentina. EcoRegistros Revista, 2, 1–6.
Lucero, F. (2014). Las aguaditas y baños de Talacasto, nuevas localidades para el Burrito Negruzco (Porzana spiloptera) y su reaparición en los Bañados del Carau, Provincia de San Juan, Argentina. Nótulas Faunísticas, 167, 1–6.
MapBiomas. (2025). Cobertura. Retrieved [2025], from https://plataforma.pampa.mapbiomas.org/cobertura?activeBaseMap=9&layersOpacity=100&activeModule=coverage&activeModuleContent=coverage%3Acoverage_changes&activeYear=2023&mapPosition=-35.263562%2C-58.408813%2C7&timelineLimitsRange=1985%2C2023&baseParams%5BterritoryType%5D=1&baseParams%5BterritoryValueType%5D=multiple&baseParams%5Bterritories%5D=1140001%3BPampa%3B1%3BBioma%3B0%3B0%3B0%3B0&baseParams%5BactiveClassTreeOptionValue%5D=default&baseParams%5BactiveClassTreeNodeIds%5D=1%2C2%2C3%2C4%2C5%2C6&baseParams%5BactiveSubmodule%5D=coverage_changes&baseParams%5ByearRange%5D=2012-2023
Maureira, A., Gutierrez, P., Marinovic, V., & Moreno, C. (2019). El Burrito negruzco (Porzana spiloptera), una nueva especie para los humedales de Chile. La Chiricoca, 24, 4–10.
Rost, G. (2017). Nuevo registro del burrito negruzco (Porzana spiloptera) para la provincia de Chubut, Argentina. EcoRegistros Revista, 7, 14–17.
Taylor, R. W., & van Perlo, B. (1998). Rails. Princeton University Press.
Zarco, A., Cuervo, P. F., & Llambías, P. E. (2017). First record of Dot-winged Crake (Porzana spiloptera, Durnford, 1877) for the central Andes in Argentina. Check List, 13, 21–23. http://dx.doi.org/10.15560/13.4.21
Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested in commenting. The window for consultation is now closed and we are unable to accept any more comments until 25 April 2025. We will now analyse and interpret the information, and we will post a preliminary decision on this species’ Red List category on this page on 25 April 2025, when discussions will re-open.
Preliminary proposal
Based on available information, our preliminary proposal for the 2025 Red List would be to list
Dot-winged Crake as Near Threatened under Criterion C2a(ii).
Many thanks to Rafael Antunes Dias for this detailed and considered reply.
A technical point on EOO: this is a minimum convex polygon around the known range, including all the area this encompasses whether suitable or not. It is intended to address the spatial distribution of threats affecting the extinction risk of the species, not to measure the area the species occupies, which is achieved through the Area of Occupancy (AOO). With confirmed breeding in Chile and southern Brazil, this species cannot approach Red List thresholds for EOO. Deriving an AOO value requires an assessment of presence and absence across the range, which is challenging for this species given the recent improvement in detection after the call became known, and uncertainty over movements.
To assess the species as Vulnerable under C2a(i) requires meeting three subcriteria:
1, the population size must be estimated at under 10,000 mature individuals
2, there must be an inferred, estimated or observed continuing decline in the population size,
3, the largest subpopulation must contain fewer than 1,000 mature individuals.
The population size for the proposed reassessment here is inferred, not estimated. As noted, the recent expansion of the range enabled by the new understanding of the vocalisations indicates that the population size is likely to be much larger than previously thought. The previous estimate of 2,500-9,999 was based on the distribution being restricted to those few coastal, saltmarsh sites in southern Brazil, Uruguay and Argentina. Many calling birds have been located where habitat has been visited with knowledge of the call: many additional sites exist that are yet to be visited by those that know the call. That supplies uncertainty but allows the inference that the overall population size is larger than previously thought.
The point made on the potential for large-scale but short-term habitat change due to fire or flood causing novel dispersal records is worth consideration. The pattern of records suggests movement is a regular habit of the species, rather than occurring in response to one-off events. Notably all records at the southern edge of the range fall between October and March, while extralimital vagrants to the north of the mapped range occur in April and May: a typical pattern for dispersing individuals in the post-breeding period. The breeding record in Chile falls in the first period, and there are numerous records of birds calling in suitable breeding habitat in this part of the range at this time of the year. Records occur year-round in Buenos Aires and Cordoba provinces, Uruguay and Brazil, and the more northerly parts of Chile. This could be explained if part of the population makes seasonal movements to access ephemeral resources. This may imply a smaller overall population size if habitat in part of the range is used seasonally, introducing further uncertainty as we cannot use the total area of habitat to approximate population size.
Alternatively, there may be a bias in search effort in the south of the range such that birds are only detected in the Austral summer, when they are present year-round. This seems unlikely, given that there is some observer effort in these areas year-round, and as noted there are records through the year further north. The IUCN criteria weights single populations more highly than multiple subpopulations, unless these really are very small. Faced with evidence that the population is not very small, it is more precautionary to assume a single population when applying Criterion C.
Given the observation that no known occupied sites appear to have lost the species, despite some being very small, and that there are records in novel wetland habitats indicating that the species can discover these sites, and that vagrant individuals have been found up to several hundred kilometres from the expected range, it is concluded the species is capable of long-range dispersal and that individuals make movements on a regular basis.
Based on the greater specialisation on saline marshes, correctly pointed out by Rafael Antunes Dias, it is plausible that the population is still small and is inferred to be declining due to habitat loss and degradation. Our preliminary proposal for the 2025 Red List would be to list Dot-winged Crake as Near Threatened, approaching thresholds under Criterion C2a(ii).
There is now a period for further comments until the final deadline on 4 May 2025, after which the recommended categorisations will be put forward to IUCN.
The final 2025 Red List categories will be published on the BirdLife and IUCN websites in October 2025, following further checking of information relevant to the assessments by both BirdLife and IUCN.
Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested in commenting. The window for consultation is now closed and we are unable to accept any more comments. We will analyse and interpret the information, and a final decision on this species’ Red List category will be posted on this page on 12 May 2025.
Recommended categorisation to be put forward to IUCN
The final categorisation for this species has not changed. Dot-winged Crake is recommended to be listed as Near Threatened, approaching thresholds under Criterion C2a(ii).
Many thanks for everyone who contributed to the 2025.2 GTB Forum process. The final Red List categories will be published on the BirdLife and IUCN websites in October 2025, following further checking of information relevant to the assessments by both BirdLife and IUCN.