Justification Although this species is more widespread than previously believed, it is only found on predator-free islands, and its overall range is very small. It is classified as Vulnerable because it is highly susceptible to the impact of any potential invasion by rats. Further surveys and monitoring, combined with ongoing conservation efforts to secure its range, could result in a downlisting to Near Threatened.

Family/Sub-family Troglodytidae

Species name author Chubb, 1909

Taxonomic source(s) Woods (1993)

Taxonomic note Troglodytes aedon (Sibley and Monroe 1990, 1993) has been split into T. aedon and T. cobbi following Woods (1993), contra SACC (2005), pending the outcome of investigation into the taxonomy of this form by SACC.

Identification 13.5 cm. Smallish, dark wren. Uniformly dark chestnut-brown upperparts. Greyer head. Pale greyish-buff underparts. Wings and tail barred dark brown and pale buff. Slender blackish bill. Voice Harsh chiz notes. Song is complex and variable, mixed phrase of trills and whistles with harsh notes.

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

9,000 - 16,000

stable

270 km²

Yes

Range & population Troglodytes cobbi has a very scattered distribution in the Falkland Islands (Malvinas). Surveys in 1983/1984-1992/1993 indicated breeding on 12 offshore islands and islets, and estimated the total population at 1,300-2,400 pairs⁴. Surveys have indicated breeding on 35 islands⁷, and estimated the total population at 4,500-8,000 pairs^3,5. Most of the islands are in small groups, separated by up to 64 km of sea, and there is no evidence to suggest an interchange between these island populations^2,4. However, it is likely that dispersing immatures are able to cross small bays⁵. In 1983, sample plots on Kidney and Carcass Islands produced population densities of four territorial males per hectare in optimum habitat and two males per hectare in less suitable conditions⁵.

Important Bird Areas Click here to view map showing IBAs where species is recorded and triggers any of the IBA criteria.

Ecology: Optimum habitat is dense tussock-grassland, growing from the high-water mark behind boulder beaches with accumulated dead kelp in which invertebrates thrive. The species is also found in rushes and among rock outcrops up to 1.6 km from coastal tussock on islands with no introduced predators. The nest is usually well-hidden in a gap amongst tussock stems or a tussock pedestal, or in a rock-crevice. Eggs are laid between early October and December, and there are probably two broods per season^2,4.

Threats The species is threatened by the potential introduction of mammalian predators to its breeding islands, especially rats (probably brown rat Rattus norvegicus) because it feeds at ground-level in exactly the habitat used by foraging rats⁵. Its present distribution is inversely related to the presence of such predators, whose impact may have increased with the historic destruction of its habitat^2,4. Rats and probably feral cats have destroyed entire populations⁴. Grazing pressure and uncontrolled fires are also potential threats⁶.

Conservation measures underway In 1998, Double and Outer Islands, off Spring Point, West Falkland, were acquired by Falklands Conservation³, and rat eradication started in 2000, covering these islands and two others, Top and Bottom Islands at Port William¹. In total, rats have now been eradicated from 22 islands⁶. Of the remaining islands within the range, 162 are known to have no introduced land predators, 75 have confirmed rats and/or mice present and a further 553 have not been surveyed (most of them are small or tiny islands)⁷.

Conservation measures proposed Continue surveys to monitor population trends. Conduct ecological studies in order to understand the necessary conditions for the species's conservation⁴. Eradicate rats from selected small islands covered with mature tussock-grass to encourage recolonisation^4,5.

References 1. R. Ingham in litt. (2000). 2. Woods (1993). 3. Woods (2000). 4. Woods and Woods (1997). 5. R. W. Woods in litt. (1999). 6. G. Munro in litt. (2007). 7. N. Huin in litt. (2007).

Text account compilers David Capper (BirdLife International), James Gilroy (BirdLife International), John Pilgrim (BirdLife International), Rob Pople (BirdLife International), Alison Stattersfield (BirdLife International)

Contributors Rebecca Ingham (Falklands Conservation), Grant Munro (Falklands Conservation), Robin W. Woods (Falklands Conservation)

IUCN Red List evaluators Stuart Butchart (BirdLife International), James Gilroy (BirdLife International)

Recommended citation BirdLife International (2009) Species factsheet: Troglodytes cobbi. Downloaded from http://www.birdlife.org on 10/2/2010

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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