Justification This species has a tiny population on two tiny islands and has undergone a rapid decline over the last ten years. For both these reasons it qualifies as Critically Endangered. It is regularly affected by extreme weather events, which cause significant fluctuations in the size of the population, and the continuing drying of the climate is a cause for serious concern. It is also under constant threat from the possibility of establishment of invasive predators. However, if attempts to create suitable conditions for re-introduction to the former range are successful, the species might be downlisted to a lower category of threat.

Family/Sub-family Mimidae

Species name author (Gould, 1837)

Taxonomic source(s) SACC (2005 + updates), Sibley and Monroe (1990, 1993), Stotz et al. (1996)

Synonyms Nesomimus trifasciatus BirdLife International (2004)

Taxonomic note The genus Nesomimus has been subsumed into the genus Mimus following SACC (2007).

Identification 25 cm. Largish, brown passerine. Dark brownish-grey upperparts. Whitish underparts with conspicuous dark patches on sides of breast. Long, graduated tail with pale tips. Longish, curved beak. Red-brown eyes. Voice Strident call. Long, melodious song. Does not mimic other birds.

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

47 - 59

decreasing

2 km²

Yes

Range & population Mimus trifasciatus survives in low numbers on Champion (0.1 km²) and Gardner-by-Floreana (0.8 km²) islets in the Galápagos Islands, Ecuador³. It became extinct on the much larger Floreana (173 km²) between 1868 and 1888¹. In 1966, the population was estimated to be no more than 150 birds⁴. Between 1980 and 1991, annual counts showed that the number of territories on Champion varied from eight to 12, averaging 10, while total numbers ranged from 24-53 birds³. On the same island between 2003 and 2007, numbers of birds varied from 20 to 52, but overall there was a downward population trend with 18 adults left in 2007⁷. A similar trend has been noted on Gardner-by-Floreana during the same period, with the number of birds on that island varying between 148 and 67, and the number of adults in 2007 just 30^7,11. A population viability analysis of the Champion population suggested that there is less than a 50% chance of the bird persisting on the island for another 100 years.

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

Ecology: It inhabits the large cactus Opuntia megasperma and other stands of vegetation, including Parkinsonia, Croton and Cordia¹. It feeds mostly on terrestrial insects, but also takes arboreal insects, fruit, nectar, pollen, centipedes, crabs, lizards and regurgitated food of boobies Sula spp.². It is a co-operative breeder, with a variable mating system².

Threats Extinction on Floreana was probably caused by the introduction of black rat Rattus rattus¹. Higher adult mortality occurs in the unusually dry La Niña years³; dry years are increasing in frequency, and this is thought to be driving the current decline⁸. The Smooth-billed Ani Crotophaga ani is known to predate other bird species on the archipelago and has been seen on Champion⁸. Increased mortality on Champion during the 1982-1983 El Niño event is thought to have been the result of avian pox virus³, and the invasive parasite Philornis downsi has been recorded¹². There are black rats present on nearby islets whose accidental introduction to either of the breeding islands poses an ever present threat⁸. The loss of immigration from the now extinct Floreana population has raised concerns for the long-term survival of the two remaining populations, as they are believed to have lost a significant amount of genetic diversity³.

Conservation measures underway A ten year action plan was developed in 2007, with plans to take active measures to safeguard existing populations, and to create suitable conditions for reintroduction to Floreana^7,8,9. The Reintroduction Plan is supported by an Emergency Plan (to enable rapid response to critical downward population trends)¹⁰, the Introduced Rodent Eradication Program initiated in 2007 and the initiation of Project Floreana, aimed at the restoration of the island⁹. The Galápagos National Park was gazetted in 1959, and includes almost all the land area of the islands. In 1979, the islands were declared a World Heritage Site⁵.

Conservation measures proposed Monitor populations and environmental conditions on both islands, preferably annually³. Further assess the stability and viability of both populations, using computer modelling of population demography³. Eradicate the Smooth-billed Ani Crotophaga ani from the two islets. Minimise chance introductions of predators and disease. Eradicate goats, pigs and donkeys and, if technology allows, R. rattus from Floreana.

References Collar et al. (1992). 1. Curry (1986). 2. Curry and Grant (1991). 3. Grant et al. (2000). 4. Harris (1968). 5. Jackson (1985). 6. Charles Darwin Foundation (2007a). 7. Charles Darwin Foundation (2007b). 8. G. Jimenez-Uzcategui in litt. (2007). 9. Anon (2008). 10. Anon (2008b). 11. Jiménez-Uzcátegui (2007). 12. Wiedenfeld & Jiménez-Uzcátegui (2008).

Further web sources of information

Alliance for Zero Extinction (AZE) species/site profile. This species has been identified as an AZE trigger due to its IUCN Red List status and limited range.

Text account compilers James Gilroy (BirdLife International), Isabel Isherwood (BirdLife International), Simon Mahood (BirdLife International), Rachel McClellan (BirdLife International), Rob Pople (BirdLife International - European Division), Rob Pople (BirdLife International), Andy Symes (BirdLife International)

Contributors T de Vries, Paquita Hoeck, Gustavo Jimenez-Uzcategui, Alan Tye

IUCN Red List evaluators Jeremy Bird (BirdLife International), Stuart Butchart (BirdLife International), Andy Symes (BirdLife International)

Recommended citation BirdLife International (2009) Species factsheet: Mimus trifasciatus. Downloaded from http://www.birdlife.org on 9/2/2010

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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