7 thoughts on “Hudson’s Canastero (Asthenes hudsoni)”
I do not support the proposal to downlist Asthenes hudsoni from Near Threatened to Least Concern. Available evidence, particularly that presented by Claramunt et al. (2022), indicates that the species likely qualifies for listing as Vulnerable under criterion A4c or at least, maintain its current category of Near Threatened. Although the major reduction in suitable breeding habitat (estimated at 65%) occurred historically (mostly in the late 20th and early 21st centuries), the species now occupies a much smaller breeding range estimated at 48,835 km², and this restricted area continues to experience a modest but ongoing decline due to anthropogenic pressures.
In Argentina, the species is largely confined to the flooding pampas, where it inhabits natural grasslands with Juncus acutus, Spartina densiflora, and Paspalum quadrifarium, typically near brackish marshes or lagoons. In Brazil, it is restricted to discrete patches of sandy coastal grasslands and saltmarshes in the external coastal plain of Rio Grande do Sul. These habitats are highly fragmented and vulnerable to multiple threats. In particular, overgrazing, expansion of wind farms, urban development, and afforestation with Pinus spp. are degrading habitat quality in Brazil. While Pinus plantations directly replace native grasslands, both Pinus and invasive Acacia species spread into grasslands, further reducing suitable habitat. Overgrazing and the recent conversion of natural grasslands into exotic forage pastures are the primary threats in the humid Pampas. This species prefers grasslands with a two-layer structure of tussocks interspersed with short grasses and may be particularly sensitive to both overgrazing and undergrazing.
Although the extent of occurrence has been estimated at approximately 77,000 km², this figure is inflated by including areas of seasonal or marginal use. Most northern records outside the humid pampas, with the exception of Brazil, are likely from the non-breeding season. The actual breeding range is much smaller and localized, and large areas of modeled suitability, particularly in Buenos Aires province, are unsuitable due to intensive cattle grazing. Claramunt et al. (2022) suggest that the true area of occupancy may be an order of magnitude smaller than their model estimates, placing the species near the threshold for Vulnerable status under criterion A4c.
There is no robust evidence that population declines have ceased, and the factors driving habitat degradation remain active. However, it is likely that the species has not undergone a decline exceeding 20% over the past 10 years. Nonetheless, I recommend that Asthenes hudsoni be considered for listing as Vulnerable (or at most Near Threatened), but not downlisted to Least Concern.
References:
Claramunt S, Aldabe J, Etchevers I, Di Giacomo AS, Kopuchian C, Milensky CM. 2022. Distribution, migratory behavior, and conservation of Hudson’s Canastero Asthenes hudsoni (Furnariidae): a grassland specialist from the humid Pampas. Avian Conservation and Ecology 17(1):25. https://doi.org/10.5751/ACE-02152-170125
Dias RA. 2018. Asthenes hudsoni (Sclater, 1874). In: Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio). Livro Vermelho da Fauna Brasileira Ameaçada de Extinção: Volume III – Aves. Brasília: ICMBio/MMA, p. 467–469.
There is wide evidence indicating that downlisting the Hudson´s Canastero (Asthenes hudsoni) from Near Threatened to Least Concern is not only a grave mistake, but also a threat to the species’ conservation. As Claramunt et al. (2022) indicated, the original area of Asthenes hudsoni’s occupancy has been reduced by 65%, and its current densities are low. The species should therefore qualify for listing as Vulnerable under IUCN criteria.
In Argentina, the Hudson´s Canastero was quite common in the Pampas grasslands, and its distribution range was much wider than it is nowadays (Sclater et al. 1888, Holland 1893, Narosky & Di Giacomo 1993). However, its populations have disappeared from many historical areas, with very low densities in most Pampas grasslands, and are concentrated in the flooding Pampas (Claramunt et al. 2022). It is no coincidence: in this subregion, one of the last remaining natural grasslands persists, but habitat degradation due to unsustainable grazing and agriculture still threatens its integrity (Comparatore et al. 1996).
The Hudson´s Canastero is a highly specialized grassland bird, with strong dependence on natural grasslands for breeding, particularly those composed of Paspalum quadrifarium (Isacch & Cardoni 2011, Trofino Falasco et al. 2024). This species prefers grasslands with two strata (tall tussocks surrounded by short grass), indicating that changes in this grassland vegetation structure will directly impact its breeding performance, as well as its ability to find shelter and food.
Given the current distribution and low densities of the species (Azpiroz et al. 2012, Claramunt et al. 2022), its specific microhabitat requirements, the extremely low breeding success (Trofino Falasco et al. 2024), and the lack of protected areas in most Pampas grasslands, I do not in any way support downlisting Astehenes hudsoni as a Least Concern.
References:
Azpiroz, A.B., Isacch, J.P., Dias, R.A., Di Giacomo, A.S., Fontana, C.S. & Palarea, C.M. 2012. Ecology and conservation of grassland birds in southeastern South America: a review. J. F. Ornithol. 83: 217–246. https://doi.org/10.1111/j.1557-9263.2012.00372.x
Claramunt, S., Aldabe, J., Etchevers, I., Di Giacomo, A.S., Kopuchian, C. & Milensky, C.M. 2022. Distribution, migratory behavior, and conservation of Hudson’s Canastero Asthenes hudsoni (Furnariidae): a grassland specialist from the humid Pampas. Avian Conserv. Ecol. 17. https://doi.org/10.5751/ACE-02152-170125
Comparatore, V.M., Martínez, M.M., Vasallo, A.I., Barg, M. & Isacch, J.P. 1996. Abundancia y relaciones con el hábitat de aves y mamíferos en pastizales de paja colorada (Paspalum quadrifarium) manejados con fuego. Interciencia 21: 228–237.
Holland, A.H. 1893. Field-Notes on the Birds of Estancia Sta. Elena, Argentine Republic. Ibis (Lond. 1859). 483–488.
Isacch, J.P. & Cardoni, D.A. 2011. Different Grazing Strategies Are Necessary to Conserve Endangered Grassland Birds in Short and Tall Salty Grasslands of the Flooding Pampas. Condor 113: 724–734. https://doi.org/10.1525/cond.2011.100123
Narosky, T. & Di Giacomo, A.S. 1993. Las aves de la provincia de Buenos Aires: distribucion y estatus.
Sclater, P.L., Keulemans, J.G. & Hudson, W.H. 1888. Argentine Ornithology: A Descriptive Catalogue of the Birds of the Argentine Republic: with Notes on Their Habits.
Trofino Falasco, C., Di Giacomo, A.S., Aranguren, M.F., Martínez Aguirre, T., Grilli, P., Paz, E.L., Pizzarello, M.G., Vera, D.G. & Berkunsky, I. 2024. Nesting biology of the Hudson´s Canastero (Asthenes hudsoni) and the Bearded Tachuri (Polystictus pectoralis), two threatened and poorly known birds of the Pampas grasslands. Stud. Neotrop. Fauna Environ. 59: 74–83. https://doi.org/10.1080/01650521.2022.2052685
Statement in Opposition to the Downlisting of Asthenes hudsoni to Least Concern
I strongly oppose the proposal to downlist Asthenes hudsoni from Near Threatened to Least Concern. In my view, such a reclassification does not reflect the current conservation reality of the species. I have been monitoring natural grasslands in the Pampas region for over a decade, particularly in areas impacted by wind farms and livestock ranching on natural grasslands of the Pampas ecoregion. Over these years, I have directly documented local population declines of A. hudsoni, and in some cases, even local extinctions. Although I do not have exact figures on the rate of decline, the continued downward trend in the number of individuals within suitable habitat is evident.
The species’ dependence on natural, structurally complex grasslands—habitats that continue to shrink and degrade due to anthropogenic pressures—makes it especially vulnerable. My field experience confirms that areas once regularly occupied by the species are now devoid of individuals, even where remnants of native grassland persist. This suggests that habitat availability alone is not sufficient for the species’ persistence if ecological integrity is compromised.
Furthermore, it is important to emphasize that the threats driving population declines—overgrazing, afforestation, the expansion of wind farms, and the conversion of natural grasslands to exotic pastures—are still very much active and even expanding. In this context, a downgrading of conservation concern sends the wrong signal and may undermine urgently needed habitat protection and management efforts.
In light of both published scientific data and long-term field observations, I believe that Asthenes hudsoni should not be downlisted. On the contrary, its current status as Near Threatened is already conservative, and there is a compelling case to consider the species for uplisting to Vulnerable under IUCN criterion A4c, as suggested by Claramunt et al. (2022). Until more robust evidence demonstrates population stabilization or recovery, downlisting would be premature and potentially harmful to the conservation of this grassland specialist.
As Coordinator of the Grasslands Program of Aves Argentinas (partner of BirdLife International), I leave below a series of elements that contribute to the evaluation of the threat category of the Hudson´s Canastero.
Habitat retraction:
The Hudson’s Canastero is a natural grassland specialist bird, whose most important populations are located within the Pampean Region of central Argentina, where grasslands have been modified by 78.02% (Nanni et al. 2020). Sixty percent of the Pampean Region is located within the Buenos Aires province, where during the period 1988-2002 the area of annual crops incorporated more than 1,200,000 hectares at the expense of the loss of grasslands (Bilenca et al. 2009). This replacement effect did not affect the entire Pampean Region with the same intensity, and while in other subregions it was profound, the Pampa Deprimida subregion has managed to maintain a good part of its grassland cover (Bilenca et al. 2009). Land use change analysis based on MapBiomas Project V4.0 (2025) data indicates that natural grassland cover for the Pampa Deprimida lost about 5% from 1998 to 2022. However, in specific sites of this subregion, the percentage of grassland loss for agricultural land reached 17% in the same period, as in the IBA “Ea. San Ignacio”. As mentioned below, the Hudson’s Canastero occupied the entire Pampean Region, and although it takes refuge in the Pampa Deprimida, it has already disappeared from a large part of its original distribution, accompanying the process of loss of natural grasslands.
Habitat requirements:
The Hudson’s Canastero requires a particular type of grassland structure, where there is a dominant species that forms tall clumps and that these clumps are separated by areas of short grass: it hides, performs its displays and nests in the tall clumps and feeds in the short grass. Depending on the region, the dominant species may be Juncus acutus, Spartina densiflora (in more saline soils) or Paspalum quadrifarium (in soils with less salt load). This original matrix occupied most of the Pampean Region; however, it has been almost completely lost and currently only persists in the Pampa Deprimida (Bilencia et al. 2009). The typical grassland of the Pampa Deprimida is the P. quadrifarium grassland (Comparatore et al. 1996; Lara & Gandini 2014). During the last two centuries, this grassland has endured the effects of unplanned grazing, often accompanied by periodic burning, plowing and the application of herbicides, generating the partial replacement of the grasslands by short, natural and cultivated grasslands (Holmberg, 1883), a process that has gained momentum from the beginning of the 19th century (Vervoorst, 1967). Habitat loss was duly mentioned by Claramunt et al. (2022), and the disappearance of the Hudson’s Canastero from 57% of the area analyzed by Bilenca et al. (2009), has been used to describe this process. Currently, isolated and relictual patches of P. quadrifarium grasslands are found (Matteucci 2012), and all of these grasslands are found within private establishments, without the protection of protected areas, which puts their permanence and sustainable management at a lot and landscape scale at risk (Costanza et al., 1997).
Reproductive biology:
The analysis by Trofino-Falasco et al. (2022) shows a strong association between P. quadrifarium grasslands and the Hudson’s Canastero: all nests studied were located within or beneath clumps of this grass species. This same study shows a worrying reproductive success rate of 4%, which ranks well below other grassland bird species, even threatened ones (Hoffmann & Rodrigues 2011; Cardoni et al. 2017).
Distribution retraction:
According to historical work, the Hudson’s Canastero was a fairly common grassland species (Sclater et al. 1888; Holland 1893). A review of historical records and collected specimens shows that its original distribution was much wider than today (Narosky & Di Giacomo 1993). Its populations have disappeared from many historical areas, also showing very low densities (Collar & Wege 1995; Azpiroz et al. 2012). An analysis of the data provided by eBird (2025) indicates a total of 930 records, for 187 localities of Hudson’s Canastero, starting in 1973 and covering a very limited area of Rio Grande do Sul, Brazil, and a single record in Uruguay, which could be considered accidental. The list of localities for the last 15 years has an average of only 17.1, which shows a very low occurrence of the species. In Argentina, the localities located in Bahía Samborombón and in specific sectors of the Pampa Deprimida where the grassland matrix required by the species persists are repeated.
Considerations on the categorization of the Hudson’s Canastero:
For all of the above, I do not support the proposal to move the Hudson’s Canastero from the NT to LC category. In future contributions I will present the arguments that accompany each of the criteria used by the IUCN to argue that the LC category is completely inappropriate. Precisely at this moment, from Aves Argentinas, a BirdLife International partner, we are working on the production of complementary information for this purpose, and our first results are completely in line with my approach.
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.
We thank all contributors for their helpful and welcome comments. All relevant information will be incorporated into the updated Red List assessment for this species. Based on the information provided, a continuing decline in mature individuals can be inferred. As a result, the population decline qualifier has been revised from ‘suspected’ to ‘inferred’.
Claramunt et al. (2022) calculated the area of suitable breeding habitat as 48,835 km2. Although it was suggested that the actual area of occupancy may be at least an order of magnitude smaller, under Criterion B2 this would still not be considered to approach the largest AOO threshold (2,000 km2). It therefore does not meet or approach threatened thresholds under this criterion.
However, further investigation into land cover change in Argentina reveals an approximate 25% loss of natural grassland habitat during the period 2010-2020 (MapBiomas Argentina Project – Collection of Annual Maps of Land Cover and Use in Argentina, accessed on 23rd April 2025: https://argentina.mapbiomas.org/). While rates of habitat loss calculated have not been restricted to the range of the species, the data on transitions of natural grassland shows a high degree of overlap with the species’ distribution, and much of this loss has occurred within its mapped range. Based on this, and the information provided in the comments above indicating that this loss is ongoing at a similar rate and that there has been local extirpation from sites in the range, it is suspected that the species is undergoing a moderately rapid decline. To account for uncertainty, the suspected rate of decline is tentatively placed in the range 10-29% over ten years. Accordingly, Hudson’s Canastero is considered to approach threatened thresholds under Criterion A.
Based on available information, our preliminary proposal for the 2025 Red List would be to list
Hudson’s Canastero as Near Threatened, approaching thresholds under Criteria A2c+3c+4c. Further input is sought however, particularly regarding specific areas where the species has been extirpated and on the ongoing rate of habitat loss.
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.
I do not support the proposal to downlist Asthenes hudsoni from Near Threatened to Least Concern. Available evidence, particularly that presented by Claramunt et al. (2022), indicates that the species likely qualifies for listing as Vulnerable under criterion A4c or at least, maintain its current category of Near Threatened. Although the major reduction in suitable breeding habitat (estimated at 65%) occurred historically (mostly in the late 20th and early 21st centuries), the species now occupies a much smaller breeding range estimated at 48,835 km², and this restricted area continues to experience a modest but ongoing decline due to anthropogenic pressures.
In Argentina, the species is largely confined to the flooding pampas, where it inhabits natural grasslands with Juncus acutus, Spartina densiflora, and Paspalum quadrifarium, typically near brackish marshes or lagoons. In Brazil, it is restricted to discrete patches of sandy coastal grasslands and saltmarshes in the external coastal plain of Rio Grande do Sul. These habitats are highly fragmented and vulnerable to multiple threats. In particular, overgrazing, expansion of wind farms, urban development, and afforestation with Pinus spp. are degrading habitat quality in Brazil. While Pinus plantations directly replace native grasslands, both Pinus and invasive Acacia species spread into grasslands, further reducing suitable habitat. Overgrazing and the recent conversion of natural grasslands into exotic forage pastures are the primary threats in the humid Pampas. This species prefers grasslands with a two-layer structure of tussocks interspersed with short grasses and may be particularly sensitive to both overgrazing and undergrazing.
Although the extent of occurrence has been estimated at approximately 77,000 km², this figure is inflated by including areas of seasonal or marginal use. Most northern records outside the humid pampas, with the exception of Brazil, are likely from the non-breeding season. The actual breeding range is much smaller and localized, and large areas of modeled suitability, particularly in Buenos Aires province, are unsuitable due to intensive cattle grazing. Claramunt et al. (2022) suggest that the true area of occupancy may be an order of magnitude smaller than their model estimates, placing the species near the threshold for Vulnerable status under criterion A4c.
There is no robust evidence that population declines have ceased, and the factors driving habitat degradation remain active. However, it is likely that the species has not undergone a decline exceeding 20% over the past 10 years. Nonetheless, I recommend that Asthenes hudsoni be considered for listing as Vulnerable (or at most Near Threatened), but not downlisted to Least Concern.
References:
Claramunt S, Aldabe J, Etchevers I, Di Giacomo AS, Kopuchian C, Milensky CM. 2022. Distribution, migratory behavior, and conservation of Hudson’s Canastero Asthenes hudsoni (Furnariidae): a grassland specialist from the humid Pampas. Avian Conservation and Ecology 17(1):25. https://doi.org/10.5751/ACE-02152-170125
Dias RA. 2018. Asthenes hudsoni (Sclater, 1874). In: Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio). Livro Vermelho da Fauna Brasileira Ameaçada de Extinção: Volume III – Aves. Brasília: ICMBio/MMA, p. 467–469.
There is wide evidence indicating that downlisting the Hudson´s Canastero (Asthenes hudsoni) from Near Threatened to Least Concern is not only a grave mistake, but also a threat to the species’ conservation. As Claramunt et al. (2022) indicated, the original area of Asthenes hudsoni’s occupancy has been reduced by 65%, and its current densities are low. The species should therefore qualify for listing as Vulnerable under IUCN criteria.
In Argentina, the Hudson´s Canastero was quite common in the Pampas grasslands, and its distribution range was much wider than it is nowadays (Sclater et al. 1888, Holland 1893, Narosky & Di Giacomo 1993). However, its populations have disappeared from many historical areas, with very low densities in most Pampas grasslands, and are concentrated in the flooding Pampas (Claramunt et al. 2022). It is no coincidence: in this subregion, one of the last remaining natural grasslands persists, but habitat degradation due to unsustainable grazing and agriculture still threatens its integrity (Comparatore et al. 1996).
The Hudson´s Canastero is a highly specialized grassland bird, with strong dependence on natural grasslands for breeding, particularly those composed of Paspalum quadrifarium (Isacch & Cardoni 2011, Trofino Falasco et al. 2024). This species prefers grasslands with two strata (tall tussocks surrounded by short grass), indicating that changes in this grassland vegetation structure will directly impact its breeding performance, as well as its ability to find shelter and food.
Given the current distribution and low densities of the species (Azpiroz et al. 2012, Claramunt et al. 2022), its specific microhabitat requirements, the extremely low breeding success (Trofino Falasco et al. 2024), and the lack of protected areas in most Pampas grasslands, I do not in any way support downlisting Astehenes hudsoni as a Least Concern.
References:
Azpiroz, A.B., Isacch, J.P., Dias, R.A., Di Giacomo, A.S., Fontana, C.S. & Palarea, C.M. 2012. Ecology and conservation of grassland birds in southeastern South America: a review. J. F. Ornithol. 83: 217–246. https://doi.org/10.1111/j.1557-9263.2012.00372.x
Claramunt, S., Aldabe, J., Etchevers, I., Di Giacomo, A.S., Kopuchian, C. & Milensky, C.M. 2022. Distribution, migratory behavior, and conservation of Hudson’s Canastero Asthenes hudsoni (Furnariidae): a grassland specialist from the humid Pampas. Avian Conserv. Ecol. 17. https://doi.org/10.5751/ACE-02152-170125
Comparatore, V.M., Martínez, M.M., Vasallo, A.I., Barg, M. & Isacch, J.P. 1996. Abundancia y relaciones con el hábitat de aves y mamíferos en pastizales de paja colorada (Paspalum quadrifarium) manejados con fuego. Interciencia 21: 228–237.
Holland, A.H. 1893. Field-Notes on the Birds of Estancia Sta. Elena, Argentine Republic. Ibis (Lond. 1859). 483–488.
Isacch, J.P. & Cardoni, D.A. 2011. Different Grazing Strategies Are Necessary to Conserve Endangered Grassland Birds in Short and Tall Salty Grasslands of the Flooding Pampas. Condor 113: 724–734. https://doi.org/10.1525/cond.2011.100123
Narosky, T. & Di Giacomo, A.S. 1993. Las aves de la provincia de Buenos Aires: distribucion y estatus.
Sclater, P.L., Keulemans, J.G. & Hudson, W.H. 1888. Argentine Ornithology: A Descriptive Catalogue of the Birds of the Argentine Republic: with Notes on Their Habits.
Trofino Falasco, C., Di Giacomo, A.S., Aranguren, M.F., Martínez Aguirre, T., Grilli, P., Paz, E.L., Pizzarello, M.G., Vera, D.G. & Berkunsky, I. 2024. Nesting biology of the Hudson´s Canastero (Asthenes hudsoni) and the Bearded Tachuri (Polystictus pectoralis), two threatened and poorly known birds of the Pampas grasslands. Stud. Neotrop. Fauna Environ. 59: 74–83. https://doi.org/10.1080/01650521.2022.2052685
Statement in Opposition to the Downlisting of Asthenes hudsoni to Least Concern
I strongly oppose the proposal to downlist Asthenes hudsoni from Near Threatened to Least Concern. In my view, such a reclassification does not reflect the current conservation reality of the species. I have been monitoring natural grasslands in the Pampas region for over a decade, particularly in areas impacted by wind farms and livestock ranching on natural grasslands of the Pampas ecoregion. Over these years, I have directly documented local population declines of A. hudsoni, and in some cases, even local extinctions. Although I do not have exact figures on the rate of decline, the continued downward trend in the number of individuals within suitable habitat is evident.
The species’ dependence on natural, structurally complex grasslands—habitats that continue to shrink and degrade due to anthropogenic pressures—makes it especially vulnerable. My field experience confirms that areas once regularly occupied by the species are now devoid of individuals, even where remnants of native grassland persist. This suggests that habitat availability alone is not sufficient for the species’ persistence if ecological integrity is compromised.
Furthermore, it is important to emphasize that the threats driving population declines—overgrazing, afforestation, the expansion of wind farms, and the conversion of natural grasslands to exotic pastures—are still very much active and even expanding. In this context, a downgrading of conservation concern sends the wrong signal and may undermine urgently needed habitat protection and management efforts.
In light of both published scientific data and long-term field observations, I believe that Asthenes hudsoni should not be downlisted. On the contrary, its current status as Near Threatened is already conservative, and there is a compelling case to consider the species for uplisting to Vulnerable under IUCN criterion A4c, as suggested by Claramunt et al. (2022). Until more robust evidence demonstrates population stabilization or recovery, downlisting would be premature and potentially harmful to the conservation of this grassland specialist.
As Coordinator of the Grasslands Program of Aves Argentinas (partner of BirdLife International), I leave below a series of elements that contribute to the evaluation of the threat category of the Hudson´s Canastero.
Habitat retraction:
The Hudson’s Canastero is a natural grassland specialist bird, whose most important populations are located within the Pampean Region of central Argentina, where grasslands have been modified by 78.02% (Nanni et al. 2020). Sixty percent of the Pampean Region is located within the Buenos Aires province, where during the period 1988-2002 the area of annual crops incorporated more than 1,200,000 hectares at the expense of the loss of grasslands (Bilenca et al. 2009). This replacement effect did not affect the entire Pampean Region with the same intensity, and while in other subregions it was profound, the Pampa Deprimida subregion has managed to maintain a good part of its grassland cover (Bilenca et al. 2009). Land use change analysis based on MapBiomas Project V4.0 (2025) data indicates that natural grassland cover for the Pampa Deprimida lost about 5% from 1998 to 2022. However, in specific sites of this subregion, the percentage of grassland loss for agricultural land reached 17% in the same period, as in the IBA “Ea. San Ignacio”. As mentioned below, the Hudson’s Canastero occupied the entire Pampean Region, and although it takes refuge in the Pampa Deprimida, it has already disappeared from a large part of its original distribution, accompanying the process of loss of natural grasslands.
Habitat requirements:
The Hudson’s Canastero requires a particular type of grassland structure, where there is a dominant species that forms tall clumps and that these clumps are separated by areas of short grass: it hides, performs its displays and nests in the tall clumps and feeds in the short grass. Depending on the region, the dominant species may be Juncus acutus, Spartina densiflora (in more saline soils) or Paspalum quadrifarium (in soils with less salt load). This original matrix occupied most of the Pampean Region; however, it has been almost completely lost and currently only persists in the Pampa Deprimida (Bilencia et al. 2009). The typical grassland of the Pampa Deprimida is the P. quadrifarium grassland (Comparatore et al. 1996; Lara & Gandini 2014). During the last two centuries, this grassland has endured the effects of unplanned grazing, often accompanied by periodic burning, plowing and the application of herbicides, generating the partial replacement of the grasslands by short, natural and cultivated grasslands (Holmberg, 1883), a process that has gained momentum from the beginning of the 19th century (Vervoorst, 1967). Habitat loss was duly mentioned by Claramunt et al. (2022), and the disappearance of the Hudson’s Canastero from 57% of the area analyzed by Bilenca et al. (2009), has been used to describe this process. Currently, isolated and relictual patches of P. quadrifarium grasslands are found (Matteucci 2012), and all of these grasslands are found within private establishments, without the protection of protected areas, which puts their permanence and sustainable management at a lot and landscape scale at risk (Costanza et al., 1997).
Reproductive biology:
The analysis by Trofino-Falasco et al. (2022) shows a strong association between P. quadrifarium grasslands and the Hudson’s Canastero: all nests studied were located within or beneath clumps of this grass species. This same study shows a worrying reproductive success rate of 4%, which ranks well below other grassland bird species, even threatened ones (Hoffmann & Rodrigues 2011; Cardoni et al. 2017).
Distribution retraction:
According to historical work, the Hudson’s Canastero was a fairly common grassland species (Sclater et al. 1888; Holland 1893). A review of historical records and collected specimens shows that its original distribution was much wider than today (Narosky & Di Giacomo 1993). Its populations have disappeared from many historical areas, also showing very low densities (Collar & Wege 1995; Azpiroz et al. 2012). An analysis of the data provided by eBird (2025) indicates a total of 930 records, for 187 localities of Hudson’s Canastero, starting in 1973 and covering a very limited area of Rio Grande do Sul, Brazil, and a single record in Uruguay, which could be considered accidental. The list of localities for the last 15 years has an average of only 17.1, which shows a very low occurrence of the species. In Argentina, the localities located in Bahía Samborombón and in specific sectors of the Pampa Deprimida where the grassland matrix required by the species persists are repeated.
Considerations on the categorization of the Hudson’s Canastero:
For all of the above, I do not support the proposal to move the Hudson’s Canastero from the NT to LC category. In future contributions I will present the arguments that accompany each of the criteria used by the IUCN to argue that the LC category is completely inappropriate. Precisely at this moment, from Aves Argentinas, a BirdLife International partner, we are working on the production of complementary information for this purpose, and our first results are completely in line with my approach.
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
We thank all contributors for their helpful and welcome comments. All relevant information will be incorporated into the updated Red List assessment for this species. Based on the information provided, a continuing decline in mature individuals can be inferred. As a result, the population decline qualifier has been revised from ‘suspected’ to ‘inferred’.
Claramunt et al. (2022) calculated the area of suitable breeding habitat as 48,835 km2. Although it was suggested that the actual area of occupancy may be at least an order of magnitude smaller, under Criterion B2 this would still not be considered to approach the largest AOO threshold (2,000 km2). It therefore does not meet or approach threatened thresholds under this criterion.
However, further investigation into land cover change in Argentina reveals an approximate 25% loss of natural grassland habitat during the period 2010-2020 (MapBiomas Argentina Project – Collection of Annual Maps of Land Cover and Use in Argentina, accessed on 23rd April 2025: https://argentina.mapbiomas.org/). While rates of habitat loss calculated have not been restricted to the range of the species, the data on transitions of natural grassland shows a high degree of overlap with the species’ distribution, and much of this loss has occurred within its mapped range. Based on this, and the information provided in the comments above indicating that this loss is ongoing at a similar rate and that there has been local extirpation from sites in the range, it is suspected that the species is undergoing a moderately rapid decline. To account for uncertainty, the suspected rate of decline is tentatively placed in the range 10-29% over ten years. Accordingly, Hudson’s Canastero is considered to approach threatened thresholds under Criterion A.
Based on available information, our preliminary proposal for the 2025 Red List would be to list
Hudson’s Canastero as Near Threatened, approaching thresholds under Criteria A2c+3c+4c. Further input is sought however, particularly regarding specific areas where the species has been extirpated and on the ongoing rate of habitat loss.
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.