• Summary
• Text account
• Data table and detailed info
• Distribution map
• Reference and further resources

Justification of Red List category
This species has a large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence under 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 size is large, and hence does not approach the thresholds for Vulnerable under the population size criterion (under 10,000 mature individuals with a continuing decline estimated to be over 10% in ten years or three generations, or with a specified population structure). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (over 30% decline over ten years or three generations). For these reasons the species is evaluated as Least Concern.

Population justification
Herzog et al. (2008) estimated the population to be 70,000-80,000 individuals. This species is considered to have a high dependency on forest habitat, and tree cover is estimated to have declined by 3.8% within its mapped range over the past 10 years (Global Forest Watch 2022, using Hansen et al. [2013] data and methods disclosed therein). It is therefore tentatively suspected that this rate of cover loss may have led to a decline of between 1-19% in the species' population size over the same time frame, with a best estimate of reduction being less than 5%.

Trend justification
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Myrmotherula grisea is restricted to the Yungas (east Andean foothills) of La Paz, Beni, Cochabamba and Santa Cruz, central and west Bolivia, and has recently been found in extreme south-west Puno, Peru (Herzog et al. 2008). In 2007 and 2009, birds were captured in the upper Urubamba Valley, Cusco, Peru, some 500 km north-west of this (Robbins et al. 2011). It occurs more or less continuously in suitable habitat across its range, and a recent study on Cordillera Mosetenes, which appears to hold over half the total population, estimated a density of 15 individuals per km² (Herzog et al. 2008).

It occurs in foothill forest with a dense, structurally complex understorey, often with Chusquea bamboo, at 600-1,500 m, but is apparently most numerous in a narrow elevational zone above the normal upper limits of its congeners White-flanked Antwren M. axillaris and Grey Antwren M. menetriesii (S. K. Herzog in litt. 1999, Herzog et al. 2008). It occurs in a variety of habitats, having been recorded in extremely wet evergreen forest (S. K. Herzog in litt. 1999), vine-tangles in the transitional zone between semi-deciduous or dry forest and riparian forest (Perry et al. 1997), and in relatively dry, semi-deciduous forest (S. K. Herzog in litt. 1999).

It is threatened by deforestation within its small geographic and elevational range, especially in La Paz and Cochabamba. Its preferred forest habitats are more accessible and easier to burn than true montane forest, with soils suited to the cultivation of staple food and export crops. Consequently, the region is a favoured target for colonists from the altiplano, and encroachment into protected areas is occurring. Exploration for natural resources takes place in Bolivia's national parks, making mining a potential future threat (B. Hennessey in litt. 1999). Nevertheless, vast amounts of pristine forest remain in inaccessible areas within the species's elevational range, although it may be excluded by the harsh climate in some of these areas (J. Fjeldså in litt. 1999, B. Hennessey in litt. 1999).

Conservation Actions Underway
A significant proportion of its range is protected in Amboró National Park (Santa Cruz), Carrasco National Park (Cochabamba), Isiboro Sécure National Park (Beni/La Paz), Pilón Lajas Biosphere Reserve and Indigenous Territory and Madidi National Park (La Paz) (Wege and Long 1995, Perry et al. 1997, S. K. Herzog in litt. 1999).

Conservation Actions Proposed
Survey remaining forests in upper tropical zone in Bolivia. Maintain the integrity of Amboró and Carrasco National Parks to ensure their integrity, particularly with respect to encroachment by settlers.

10 cm. Small, arboreal, gleaning antwren showing strong sexual dimorphism. Male entirely uniform grey, with unmarked wing-coverts. Female olivaceous-brown above with more rufescent unmarked wings and tail and uniformly bright ochraceous underparts. Voice Series of eight loud but melancholic kíu or kee calls at same pitch and pace. Also harsh, chattery calls.

Text account compilers
Rutherford, C.A.

Contributors
Fjeldså, J., Hennessey, A., Herzog, S., MacLeod, R. & Tobias, J.

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Recommended citation
BirdLife International (2024) Species factsheet: Ashy Antwren Myrmotherula grisea. Downloaded from https://datazone.birdlife.org/species/factsheet/ashy-antwren-myrmotherula-grisea on 23/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from https://datazone.birdlife.org/species/search on 23/12/2024.