Justification This species is listed as Critically Endangered because it is estimated to have an extremely small population which is declining owing to predation by introduced mammals. In addition, it has a very small range, and its habitat is declining in quality and extent.

Family/Sub-family Zosteropidae

Species name author (Vieillot, 1817)

Taxonomic source(s) Dowsett and Forbes-Watson (1993), Sibley and Monroe (1990, 1993)

Synonyms Zosterops chloronothos BirdLife International (2000), Zosterops chloronothos Sibley and Monroe (1990, 1993), Zosterops chloronothos Collar et al. (1994)

Identification 10 cm. Small, drab, warbler-like bird of forest. Dull olive-green above with paler underparts, tending towards cream on belly and yellow on vent. Similar spp. Confused only with Mauritius Grey White-eye Z. borbonicus mauritianus from which it differs by having dark, not grey rump, noticeable white eye-ring, and being overall olive, not grey. Also has longer, fine, decurved bill. Voice Metallic plik plik contact note and warbled song. Hints Not easy to find in the Black River Gorge area in south-west Mauritius.

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

190 - 296

decreasing

61 km²

Yes

Range & population Zosterops chloronothus is endemic to Mauritius. It declined rapidly from 350 pairs in the mid-1970s, to c.275 pairs by the mid-1980s. Intensive fieldwork during 1990-1993 indicated a further reduction to an estimated 200 pairs⁵, and fieldwork between 1998 and 2001 concluded that the global population size lay within the range 93-148 pairs^8,9,11 within an area of less than 25 km² located in the southwest of the Black River Gorges National Park. It is widespread in upland native forest, but largely absent from the whole Macchabé-Brise Fer area and Fouge Range⁵. The species's core distribution has contracted since 1975 - it has disappeared from three outlying sites (Tamarin Falls, Jouanis and Monvert) and the core area has decreased by 50%¹⁰. Its status in central Mauritius (Montagne Lagrave and the central plateau relics) remains unsurveyed^8,9. Highest densities are between Montagne Cocotte and Combo Forest with up to 10 pairs/km^{2 3}. Birds exploit isolated habitats over a wide area of the central plateau, including many relict patches of native vegetation⁵. Following twenty years of conservation work on Ile aux Aigrettes, 16 white-eyes were released on the predator free island between December 2006 and March 2007¹¹. A further release of around 20 birds in December 2007 will further the establishment of a small sub-population on Ile aux Aigrettes.

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

Ecology: It is restricted to the wettest native upland forests. It feeds on both nectar and insects, and travels considerable distances to productive flowers¹. Some introduced plant species have become extremely important nectar sources⁴. High densities may be associated with mosaics of small plantations of exotic trees, where nest-predation may be low, interspersed with native vegetation for foraging⁵. They have large non-exclusive home ranges but aggressively defend a territory around a favoured flower or nest-site against conspecifics and Mauritius Grey White-eye Z. borbonicus mauritianus¹⁰. In recent decades pairs have not fledged more than one offspring per nesting attempt and productivity was 7-17% during three study seasons¹⁰. In more recent study seasons (2005-2008) productivity has been higher and pairs have often been seen to fledge two chicks per nesting attempt. Harvests/rescues of wild nests have shown that the clutch-size is 1-3 eggs¹².

Threats Z. chloronothus has suffered chronically from continuing habitat destruction and degradation as a result of invasion by exotic plants. Nest predation by introduced mammals and birds is considered a major threat^3,10: a study of Mauritius Grey White-eye found only 8% of nests resulted in fledglings, with predation by native Mauritius Black Bulbul Hypsipetes olivaceus and probably the invasive Red-whiskered Bulbul Pycnonotus jocosus the most frequent cause of nest failure¹³.

Conservation measures underway The species has long been protected by law. The Black River National Park partly covers the species's distribution. Habitat around Bassin Blanc may be bought by compulsory purchase in the future^2,7. A species recovery programme was initiated by the Mauritian Wildlife Foundation in September 2005, in which territories identified in the most recent survey were revisited and the breeding behaviour of these birds was closely monitored¹². Over the past three seasons (2005-2008) an intensive management plan has been applied, involving wild population monitoring, predator control at nest sites, rescue/harvest of wild nests, artificial incubation and hand-rearing of offspring and a trial release of birds to the predator-free, restored offshore islet Ile aux Aigrettes (December 2006)¹². The aims of this programme are to increase knowledge of the species and its current threats, and investigate management techniques with a view to designing a long-term management strategy¹². Rehabilitation of native vegetation in small plots has been initiated through exclusion of exotic plants and animals, and there is ongoing research to assess benefits to native birds⁶. Sixteen individuals, all originating from wild nests were released onto Ile aux Aigrettes in 2006 and this intensive management was continued in 2007 with a further 20 birds released onto the islet¹². The Ile aux Aigrettes sub-population is closely monitored and provided with supplementary food and two breeding pairs have so far been identified. Further releases of birds to Ile aux Aigrettes will facilitate the establishment of a small subpopulation. Several individuals from rescued nests were hand-reared by a team from Chester Zoo, the Durrell Wildlife Conservation Trust and the Mauritian Wildlife Foundation¹³, but captive breeding of the Mascarene Grey White-eye Zosterops barbonicus was unsuccessful and it is now thought that releases to predator-free islets and effective management of upland habitat are more viable options for conserving the Mauritius Olive White-eye¹².

Conservation measures proposed Continue population monitoring. Continue rehabilitation of native forest in appropriate areas to improve food sources for the species. Continue releases on Ile aux Aigrettes^5,10 using wild rescued/harvested birds in order to establish a breeding population. Develop Conservation Management Areas (CMAs) within the species's current range which have high densities of important nectar-producing plants and where predators are strictly controlled¹⁰. Initiate studies to investigate habitat requirements with view to developing habitat enrichment programmes and future species management techniques.

References 1. Cheke (1987b). 2. Jones and Hartley (1995). 3. C. Jones in litt. (2000). 4. Safford (1991). 5. Safford (1997c). 6. Safford and Jones (1998). 7. R. Safford in litt. (1999). 8. R. Switzer in litt. (2003). 9. Nichols et al. (2004). 10. Nichols et al. (2005). 11. Anon (2006). 12. R. Cole in litt. (2007). 13. Sørensen (2005).

Text account compilers Phil Benstead (BirdLife International), Jeremy Bird (BirdLife International), Jonathan Ekstrom (BirdLife International), Rachel McClellan (BirdLife International), Sue Shutes (BirdLife International), Andy Symes (BirdLife International), Ben Warren (BirdLife International)

Contributors Ruth Cole (Mauritian Wildlife Foundation), Carl Jones (Mauritian Wildlife Foundation), R. Nichols (Queen Mary University of London), Roger Safford (BirdLife International), R. Switzer

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

Recommended citation BirdLife International (2009) Species factsheet: Zosterops chloronothus. 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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