One thought 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.
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.