Overview

Brief Summary

Introduction

Troglodytes cobbi (Cobb’s wren) is a wren found only in the Falkland islands. Troglodytes cobbi is named Cobb’s wren after Arthur F. Cobb who collected the first specimen from which the species was described on Carcass Island, Falkland Islands, in July 1908.Classified as ‘Vulnerable’ to extinction by the IUCN due to
  • the very small overall range (270km²) of the wrens habitat
  • living on islands with a high susceptibility to invasion by rats


Threats
Under threat predominantly from the potential
  • introduction of mammalian predators to islands where it breeds
  • the loss of its natural tussac habitat by burning and livestock grazing
  • cannot survive on islands in the presence of rats
    • may co-exist with a few domestic cats on larger islands
    • feral cats and rats have probably already destroyed whole populations
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Taxonomy

Cobb’s wren forms a superspecies with:
  • Troglodytes aedon
  • T. brunneicollis
  • T. musculus
  • T. tanneri
  • T. beani


Morphology
  • Crown and nape grey-brown, becoming browner on the back and shoulders and brighter rusty-brown on the rump.
  • Primaries and secondaries blackish-grey on inner webs, the outer webs with warm brown transverse bars, forming alternating ‘black and brown’ bars visible on the closed wing.
  • Rectrices warm brown, with narrow blackish bars across the entire tail.
  • Lores, cheeks and ear-coverts unmarked grey-brown; chin and throat lighter grey-brown.
  • Chest and belly unmarked grey-brown; flanks and undertail coverts rusty-brown.
  • Iris brown; bill blackish; legs dark brown.


Diagnostic description
A dark wren with uniformly dark chestnut-brown upperparts, pale greyish-buff underparts and greyish head. Wings and tail barred blackish and pale buff. Slender backish bill.Similar in appearance to Northern and Southern house wrens (Troglogytes aedon and T. musculus), though distinguished by its larger size, generally greyer plumage and very different ecology.

Look alikes
The only other wren present on the Falkland Islands is the Sedge Wren (Cistothorus platensis), which is smaller, shorter-billed, paler, and with obvious black and buff striations on the shoulders
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Comprehensive Description

Biology

Size
  • Length: 12 – 13 cm long (bill tip to tail tip)
  • Weight: 19.1g (mean), 17g - 20g (min-max)


Reproduction
  • Song heard between late August and mid-April.
  • Strongly territorial during breeding and faithful to territory from year to year.
  • The nest is a domed ball made of grasses with an entrance hole 6cm to 8cm wide near the top. It is lined with soft feathers of several species and is usually well hidden in tussac stems, a tussac pedestal or in a rock crevice between ground level and 60 cm above ground.
  • Three to four pinkish eggs, covered with tiny red or light brown spots, are laid between early October and December. Two broods are probably reared in a season.
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Distribution

Range Description

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 pairs (Woods and Woods 1997). In later years, surveys indicated breeding on 35 islands (N. Huin in litt. 2007), and estimated the total population at 4,500-8,000 pairs (R. W. Woods in litt. 1999, Woods 2000). Currently it is estimated to breed on 70 islands, half of which are smaller than 50 ha (Woods and Otley 2008). 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 (Woods 1993, Woods and Woods 1997). However, it is likely that dispersing immatures are able to cross small bays (R. W. Woods in litt. 1999). 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 conditions (R. W. Woods in litt. 1999).

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Range

Falkland Islands.
  • Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2014. The eBird/Clements checklist of birds of the world: Version 6.9. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/

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Ecology

Habitat

Habitat and Ecology

Habitat and 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 1.6km 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 (Woods 1993, Woods and Woods 1997).


Systems
  • Terrestrial
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General Ecology

Distribution ecology

Distribution
Endemic to the Falkland Island archipelago were it is only found on small offshore, predator-free islands.

Habitat
Associated with tussac grass (Parodiochloa flabellata), a very tall and dense Falkland plant.Optimum habitat is dense tussac-grassland growing from the high-water mark behind boulder beaches with accumulated dead kelp in which invertebrates thrive.It also occurs in rushes and among rock outcrops up to 1 mile from coastal tussac.

Population biology
Surveys in 1998/1999 estimated the total population at 4,500 – 8,000 pairs.
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Life History and Behavior

Behavior

Behaviour

Generally tame and confiding.Feeds in tussock grass and among boulders, moving mouse-like between crevices.When disturbed will disappear silently under cover in preference to flying.

Migration
Sedentary.No evidence of movement other than possibly between closely adjacent islands.

Feeding
Feeds on invertebrates for which it forages in tussac grass, around and under boulders and among washed-up kelp on beaches.Food items include:
  • Small insects
  • Lice
  • Crickets
  • Moth larvae
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Molecular Biology and Genetics

Molecular Biology

Barcode data: Troglodytes cobbi

The following is a representative barcode sequence, the centroid of all available sequences for this species.


No available public DNA sequences.

Download FASTA File
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Statistics of barcoding coverage: Troglodytes cobbi

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 8
Specimens with Barcodes: 8
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
D2

Version
3.1

Year Assessed
2015

Assessor/s
BirdLife International

Reviewer/s
Symes, A. & Butchart, S.

Contributor/s
Ingham, R., Munro, G. & Woods, R.W.

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.


History
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Not Recognized (NR)