Archived 2010-2011 topics: Hudson’s Canastero (Asthenes hudsoni): request for information

Link to BirdLife species factsheet for Hudson’s Canastero

Hudson’s Canastero Asthenes hudsoni is currently listed as Least Concern on the basis that it does not approach the thresholds for Vulnerable under any of the IUCN criteria.

This species has an Extent of Occurrence (EOO) estimated at 590,000 km2, and hence does not approach the thresholds for Vulnerable under the range size criterion (EOO of less than 20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend is apparently not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds under the population trend criterion (at least a 30% decline over ten years or three generations). The population size has apparently not been quantified, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (fewer than 10,000 mature individuals with a continuing decline estimated to be at least 10% over ten years or three generations, or with a specified population structure).

Despite its global status as Least Concern, this species is considered ‘vulnerable’ at the national level in Argentina, although in this assessment the categories and criteria differed markedly from those provided by the IUCN (López-Lanús et al. 2008). Its status in Argentina, where it is considered rare (J. Lowen in litt. 2009), is thus considered at risk of worsening (López-Lanús et al. 2008). It is also rare in Uruguay, with only about 10 records as of August 2009 (J. Aldabe in litt. 2009). In Uruguay at least, the species’s population density is potentially being reduced by conversion of its habitat to pasture and cultivation.

With these observations in mind, up-to-date information is requested for this species, including details of its likely population size, estimated population trend over 11 years (estimate of three generations) and the severity of potential threats. Any new information on this species will help in the evaluation of its global threat status.

López-Lanús, B., Grilli, P., Di Giacomo, A. S., Coconier, E. E. and Banchs, R. eds. (2008) Categorización de las aves de La Argentina según su estado de conservación. Informe de Aves Argentinas/AOP y la Secretraría de Ambiente y Desarrollo Sustentable. Buenos Aires, Argentina: Aves Argentinas/AOP.

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2 Responses to Archived 2010-2011 topics: Hudson’s Canastero (Asthenes hudsoni): request for information

  1. Although the known range of this species is large, it’s important to consider that this range includes many points that correspond to winter records (where the species probably doesn’t breed). Although it’s known from localities in the center and north of Buenos Aires, southern santa fe, eastern Cordoba, and Southern Entre Rios, the largest populations are found is the Bahia de Samboronbon and watershed of the Rio Salado in the Province of Buenos Aires. At those two areas, where the habitat is optimal, the species is common and you can see a pair every 400 m. In the rest of its distribution, you find it’s habitat only in patches, and the species is very difficult to find. There is hardly any habitat that would seem suitable, north of Southern Santa Fe, and we have never found it there.

    Asthenes hudsoni’s habitat in northeast Buenos Aires is preferably continuous grasslands of Spartina densiflora in a soil that floods in winter. Also it’s found on the edge of roads where this environment is maintained.

    The species survives in pastures with cows, but doesn’t survive the replacement of these grasslands by urbanization, drainage, and crops.

    It has lost quite a bit of habitat to urbanization, drainage and crops. This habitat loss is ongoing and acelerating. The seasonal wetlands inhabited by Asthenes hudsoni are considered by most people to be useless lands that need to be drained, filled in and made useful. Cows can live in the seasonal wetlands, but they are not great places for cows, and in the last few years, there is a lot more conversion to crops and urban areas than to cows; indeed, every day there are fewer cows and more people and crops here.

    In the Rio Lujan watershed (cuenca Escobar, North of Buenos Aires, Highway 8 and North, Partido de Escobar and Partido de Pilar) it had lots of habitat (thousands of hectares) and was easy to find until the end of the 1970s. Today there is no more habitat there; instead there are gated communities.

    In 250 km from Partido de San Nicolas to Capital Federal, in the last 30 years the species has lost 70% of its habitat or more.

    In the watershed of the Rio Salado, habitat loss is ongoing. In the Bahia de Samborombon, because it is an area that floods frequently by the estuary, the land isn’t too useful currently for human uses, so for now the habitat is not seriously threatened there.

    If we compare with Spartonoica maluroides, a species considered Near Threatened, and which shares a large part of the range and habitat, Asthenes hudsonii is much rarer. Where they are found together, there are 10 Spartonoica for each 1 Asthenes. And Spartonoica is also found in many localitites where you can’t find Asthenes, whereas you don’t find (or only rarely) Asthenes without Spartonoica.

    For these reasons, we think the species could classify as near threatened or even Vulnerable.

  2. James Lowen says:

    I was astonished when I learnt last year that Hudson’s Canastero was Least Concern.

    Much of what Lui and Alejandro write accords with my (limited) personal experience. Hudson’s Canastero is a much rarer bird than Bay-capped Wren-Spinetail, this being obvious due to regular co-existence at sites.

    I am surprised at the range size of 590,000 km2. I assume this relates – as Lui and Alejandro suggest – to winter records as well as breeding sites. I wonder whether this is consistent with other threatened species.

    One data point missing from the BirdLife intro is the species’s recent discovery in Rio Grande do Sul, Brazil – see recent note in Cotinga.

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