Cobb’s wren (Troglodytes cobbi)

Also known as: house wren, rock wren (in the Falkland Islands)
Synonyms: Troglodytes aedon cobbi
KingdomAnimalia
PhylumChordata
ClassAves
OrderPasseriformes
FamilyTroglodytidae
GenusTroglodytes (1)
SizeLength: 12 cm (2)
Weight17 – 20 g (3)

Cobb's wren is classified as Vulnerable (VU) on the IUCN Red List (1).

Cobb’s wren (Troglodytes cobbi) is a small, charismatic bird (4), found only on the Falkland Islands archipelago. A somewhat dull coloured bird, Cobb’s wren has uniformly dark chestnut-brown upperparts, pale grey under-parts and a grey-brown head. The wings and tail are barred dark brown and chestnut. The distinctively long and slightly down-curved bill is black and the eyes and legs are brown. It is often seen moving from boulder to boulder like a mouse, and will disappear from disturbances in this way, in preference to flying (5).

Cobb’s wren is found on about 100 offshore (6) (7), predator-free islands in the Falkland Islands archipelago, including Sea Lion, Carcass, Speedwell, Lively and most of the Jason Islands group (4) (5) (8).

Found most commonly around the tussac grassland behind kelp-strewn, boulder beaches. Cobb’s wren is also found in rushes and amongst rock outcrops, up to one and a half kilometres from the coast (1) (5) (8).

Breeding between October and December, Cobb’s wren lays three or four eggs per clutch in a dome-shaped nest built by the male of grasses, with an entrance hole near the top (1) (3) (4) (8) (9). The nest is lined with the soft feathers of several bird species, and is well hidden in tussac grass or in a rock crevice (3) (4), between ground level and 60 centimetres above the ground (5). It is possible that a breeding pair will produce two clutches a year. Cobb’s wren is tame and disregards human presence if it does not feel threatened, often feeding near them (2).

Cobb’s wren feeds on invertebrates found within dead kelp on beaches, within tussac grass, and under or around boulders (2) (8). Although often difficult to see, Cobb’s wren will reveal its presence through song, a mixed phrase of rapid trills, whistles and harsh notes, used to defend territories and attract mates during the breeding season (9) (10). Males on Carcass Island have been shown to live for at least six years, and probably stay in the same territory for life (4) (10).

With a distribution already limited to the 750 plus archipelago of the Falkland Islands, Cobb’s wren has apparently become locally extinct on many of the offshore islands and the two main islands, East and West Falkland. Those islands with suitable Cobb’s wren habitat, such as tussac, other vegetation and boulder beaches with kelp, but with populations of introduced mammals, such as brown rat (Rattus norvegicus) and feral cats, have been found to lack any Cobb’s wren populations. There is currently no concrete evidence that such mammals predate Cobb’s wren, but there is a mass of circumstantial evidence showing that when these mammals establish on islands with Cobb’s wren, it is lost from the islands within a few years. Rats hunt along the shoreline where Cobb’s wren prefers to forage, so it is therefore reasonable to assume that rats come into conflict with Cobb’s wren. Cobb’s wren is also threatened by the loss of its habitat, through livestock grazing and fires (1) (4) (8).

Rat eradication programs started on the islands in 2001 (6). So far, eradications to remove rats have been attempted on 56 islands, with 20 of these confirmed as successful to date (7). There are established rat populations on at least a further 41 islands and probably many more (8).

Proposed conservation plans for Cobb’s wren include continued surveys to obtain some population numbers, with further studies to help understand the ideal conditions for conservation. Further rat eradication is planned on islands carrying tussac grass to encourage re-colonisation (1) and it is probable that through the eradication of invasive predators and knowledge gained from surveys, Cobb’s wren could be reclassified as Near Threatened (1).

Bio-security plans and management plans are being put in place to reduce the chances of accidental introduction of further invasive species to islands with Cobb’s wren populations (4).

For more information on conservation in the Falkland Islands, see:

For more information on the conservation of birds, see:

For more information on Cobb's wren and other bird species please see:

Authenticated (27/10/10) by Robin W Woods, MBE FLS, ornithologist and botanist, resident in Devonshire UK, and Nick Rendell, Environmental Officer, Falkland Islands Government.
http://www.epd.gov.fk

  1. IUCN Red List (September, 2010)
    http://www.iucnredlist.org/
  2. Ridgely, R.S. and Tudor, G. (2009) Field Guide to the Songbirds of South America: The Passerines. University of Texas Press, Texas.
  3. Natural History Museum - Cobb's wren (September, 2010)
    http://www.nhm.ac.uk/nature-online/species-of-the-day/biodiversity/endangered-species/troglodytes-cobbi/index.html
  4. Woods, R. and Otley, H. (2008) A Species Action Plan for Cobb’s Wren: 2009 – 2019. Falklands Conservation, Falkland Islands. Available at:
    http://www.falklandsconservation.com/news/2009/Cobbs_Wren_SAP_FINAL.pdf
  5. Falklands Conservation - Cobb's wren (September, 2010)
    http://www.falklandsconservation.com/wildlife/birds/cobbswren.html
  6. Woods, R. (October, 2010) Pers. comm.
  7. Poncet, S. (October, 2010) Pers. comm.
  8. BirdLife International - Cobb's wren (September, 2010)
    http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=9769&m=0
  9. Perrins, C. (2009) The Encyclopedia of Birds. Oxford University Press, Oxford, UK.
  10. Woods, R.W. and Woods, A. (2006) Birds and Mammals of the Falkland Islands. Wildguides, Hampshire, UK.