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Troglodytes cobbi

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA AVES PASSERIFORMES TROGLODYTIDAE

Scientific Name: Troglodytes cobbi
Species Authority: Chubb, 1909
Common Name(s):
English Cobb's Wren
Taxonomic Notes: 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.

Assessment Information [top]

Red List Category & Criteria: Vulnerable D2 ver 3.1
Year Published: 2012
Date Assessed: 2012-05-01
Assessor(s): BirdLife International
Reviewer(s): Symes, A. & Butchart, S.
Contributor(s): Ingham, R., Munro, G. & Woods, R.W.
Facilitator/Compiler(s): Gilroy, J., Pilgrim, J., Pople, R., Sharpe, C J
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.

Geographic Range [top]

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).

Countries:
Native:
Falkland Islands (Malvinas)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: An estimate of 9,000-16,000 individuals is given by Woods (2000). In 2008 this estimate had remained unchanged at 9,000-16,000 individuals or 6,000 pairs (12,000 mature individuals).
Population Trend: Stable

Habitat and Ecology [top]

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 1.6 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 (Woods 1993, Woods and Woods 1997).

Systems: Terrestrial

Threats [top]

Major Threat(s): 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 rats (R. W. Woods in litt. 1999). Its present distribution is inversely related to the presence of such predators, whose impact may have increased with the historic destruction of its habitat (Woods 1993, Woods and Woods 1997). Rats and probably feral cats have destroyed entire populations (Woods and Woods 1997). Grazing pressure and uncontrolled fires are also potential threats (G. Munro in litt. 2007).

Conservation Actions [top]

Conservation Actions: Conservation Actions Underway
In 1998, Double and Outer Islands, off Spring Point, West Falkland, were acquired by Falklands Conservation (Woods 2000), and rat eradication started in 2000, covering these islands and two others, Top and Bottom Islands at Port William (R. Ingham in litt. 2000). In total, rats have now been eradicated from 22 islands (G. Munro in litt. 2007). 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) (N. Huin in litt. 2007).

Conservation Actions Proposed
A conservation action plan has been produced (Woods and Otley 2008). Continue surveys to monitor population trends. Conduct ecological studies in order to understand the necessary conditions for the species's conservation (Woods and Woods 1997). Eradicate rats from selected small islands covered with mature tussock-grass to encourage recolonisation (Woods and Woods 1997, R. W. Woods in litt. 1999).


Citation: BirdLife International 2012. Troglodytes cobbi. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 01 August 2014.
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