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Troglodytes cobbi
– Vulnerable
Taxonomy
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Kingdom:
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ANIMALIA
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Phylum:
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CHORDATA
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Class:
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AVES
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Order:
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PASSERIFORMES
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Family:
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TROGLODYTIDAE
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Scientific Name:
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Troglodytes cobbi
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Species Authority:
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Chubb, 1909
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Common Name/s:
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Taxonomic Notes:
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Troglodytes aedon (Sibley and Monroe 1990, 1993) is 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.
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Assessment Information
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Red List Category & Criteria:
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VU D2 ver 3.1 (2001)
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Year Assessed:
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2006
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Assessor/s:
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BirdLife International
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Evaluator/s:
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Butchart, S. & Pilgrim, J. (BirdLife International Red List Authority)
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Justification:
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Although this species is more widespread than previously believed, it is only found on tiny, predator-free offshore islets, 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.
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History:
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| 1994 | - | Vulnerable (Collar, Crosby and Stattersfield 1994) |
| 2000 | - | Vulnerable (BirdLife International 2000) |
| 2004 | - | Vulnerable (BirdLife International 2004) |
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Geographic Range
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Range Description:
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Troglodytes cobbi has a very scattered distribution in the Falkland Islands (to UK). 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 in 1997/1998 indicated breeding on 29 islands, and estimated the total population at 4,500-8,000 pairs3,5. 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 populations2,4. 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.
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Countries:
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Native:
Falkland Islands (Malvinas)
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Population
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Population Trend:
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Habitat and Ecology
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Habitat and Ecology:
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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 season2,4.
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System:
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Terrestrial
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Threats
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Threats:
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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 habitat2,4. It can co-exist with a few domestic cats on large islands, but rats and feral cats have probably destroyed entire populations4.
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Conservation Actions
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Conservation Actions:
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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.
Conservation measures proposed:
Continue surveys to confirm population estimates and trend. 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 recolonisation4,5.
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