One thought 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.
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