Justification This species qualifies as Vulnerable owing to its very small population and range, and hence its susceptibility to invasion by a mammalian predator.

Family/Sub-family Troglodytidae

Species name author Townsend, 1890

Taxonomic source(s) AOU checklist (1998 + supplements), Sibley and Monroe (1990, 1993), Stotz et al. (1996)

Identification 13 cm. Plain, grey-brown wren. Buff supercilium and eye-ring. Dark barring on tail and wings. Pale buff underparts, barred darker on undertail. Voice Long, dry insect-like rattle. Also chattering and tchek notes. Song similar to House Wren T. aedon.

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

340 - 400

stable

33 km²

Yes

Range & population Troglodytes tanneri is endemic to Isla Clarión in the Revillagigedo Islands, Mexico. Only 20 individuals were recorded in 1986¹, but subsequent visits to the island have found the species to be common^2,4. The population was estimated at 170-200 pairs in 1988, with the highest densities around buildings and adjacent areas².

Ecology: It occurs in all habitats throughout the island from rocks on the beach to shrubbery at the highest elevations⁴. Nests are built in bushes, cacti, buildings and derelict vehicles^3,4.

Threats Introduced herbivores have extensively modified the native vegetation on Clarión⁵, but this has not impacted upon this species. However, introduced rabbits Oryctolagus cuniculus may subsidise native predators, such as Burrowing Owl Athene noctua and racer snake Coluber sp. and increase their impact on wren populations. The introduction of a mammalian predator would have extremely serious consequences. The possibility of a cat introduction is small, but mouse or rat introductions are more likely⁶, and there is no active introduction prevention plan in place⁸.

Conservation measures underway The Revillagigedo Islands were declared a biosphere reserve in 1994⁵. There is a plan to eradicate introduced herbivores from Clarión; pigs and sheep have already been eradicated but rabbits remain^6,7. The Mexican navy restricts access to the island and helps to prevent further introductions^6,8.

Conservation measures proposed Carry out surveys to obtain an up-to-date population estimate. Monitor population trends through regular surveys. Eradicate introduced rabbits from Clarión. Continue to prevent the introduction of mammalian predators.

References 1. Everett (1988). 2. Howell and Webb (1989). 3. Howell and Webb (1995a). 4. Santaella and Sada (1991). 5. Stattersfield et al. (1998). 6. B. Tershy in litt. (1999). 7. Aguirre et al. In press. 8. B. Tershy and B. Keitt in litt. (2007).

Text account compilers David Capper (BirdLife International), Isabel Isherwood (BirdLife International), Simon Mahood (BirdLife International), Rob Pople (BirdLife International)

Contributors Brad Keitt (Island Conservation), Bernie Tershy (Island Conservation)

IUCN Red List evaluators Stuart Butchart (BirdLife International), Simon Mahood (BirdLife International)

Recommended citation BirdLife International (2009) Species factsheet: Troglodytes tanneri. Downloaded from http://www.birdlife.org on 9/2/2010

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

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