Zosterops chloronothus 

Scope: Global

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Passeriformes Zosteropidae

Scientific Name: Zosterops chloronothus
Species Authority: (Vieillot, 1817)
Common Name(s):
English Mauritius Olive White-eye
French Oiseau-lunettes de l'Ile Maurice
Zosterops chloronothos chloronothos Collar et al. (1994)
Zosterops chloronothos chloronothos Sibley and Monroe (1990, 1993)
Zosterops chloronothos chloronothos BirdLife International (2000)
Identification information: 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.

Assessment Information [top]

Red List Category & Criteria: Critically Endangered C2a(ii) ver 3.1
Year Published: 2012
Date Assessed: 2012-05-01
Assessor(s): BirdLife International
Reviewer(s): Taylor, J. & Butchart, S.
Contributor(s): Cole, R., Jones, C., Nichols, R., Safford, R., Switzer, R. & Tatayah, V.
Facilitator/Compiler(s): Benstead, P., Bird, J., Calvert, R., Ekstrom, J., McClellan, R., Shutes, S., Symes, A., Warren, B.
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.

Previously published Red List assessments:

Geographic Range [top]

Range Description: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 pairs (Safford 1997c), and fieldwork between 1998 and 2001 concluded that the global population size lay within the range 93-148 pairs (R. Switzer in litt. 2003, Nichols et al. 2004, Anon 2006) 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 Range (Safford 1997c). 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% (Nichols et al. 2005). Its status in central Mauritius (Montagne Lagrave and the central plateau relics) remains uncertain (R. Switzer in litt. 2003, Nichols et al. 2004), although one was seen on Mt Lagrave in the breeding season in 2011/2012 (V. Tatayah in litt. 2012). Highest densities are between Montagne Cocotte and Combo Forest with up to 10 pairs/km2 (C. Jones in litt. 2000). Birds exploit isolated habitats over a wide area of the central plateau, including many relict patches of native vegetation (Safford 1997c). 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 2007 (Anon 2006). A further release of around 20 birds in December 2007 aimed to further the establishment of a small sub-population on Ile aux Aigrettes, and birds have since successfully fledged young there in the 2007/08, 2008/09 and 2010/11 seasons (nine pairs and a total of six fledged young) (Anon. 2011). In March 2011 the population on Ile aux Aigrettes stood at 25 (Anon. 2011), with 26 individuals in March 2012 (V. Tatayah in litt. 2012).
Countries occurrence:
Additional data:
Estimated area of occupancy (AOO) - km2:32Continuing decline in area of occupancy (AOO):Yes
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:61
Continuing decline in extent of occurrence (EOO):YesExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:8Continuing decline in number of locations:Yes
Extreme fluctuations in the number of locations:NoLower elevation limit (metres):200
Upper elevation limit (metres):600
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The population estimate of 190-296 mature individuals is derived from Nichols et al. (2004) and R. Switzer in litt. (2003). The mainland population is believed to contain over 90% of mature individuals, but this may change if the population on Iles aux Aigrettes increases in future.

Trend Justification:  Surveys have revealed that the population size declined from an estimated 346 pairs in 1975 to c.200 pairs in 1993 and 93-148 pairs in 2001 (Nichols et al. 2004), and just 7-17% of nesting attempts successfully fledged one chick between 1998 and 2001, hence current rapid declines are likely to continue into the future.

Current Population Trend:Decreasing
Additional data:
Number of mature individuals:190-296Continuing decline of mature individuals:Yes
Extreme fluctuations:NoPopulation severely fragmented:No
No. of subpopulations:2Continuing decline in subpopulations:No
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No
No. of individuals in largest subpopulation:100

Habitat and Ecology [top]

Habitat and Ecology:It is restricted to the wettest native upland forests. It feeds on both nectar and insects, and travels considerable distances to productive flowers (Cheke 1987b). Some introduced plant species have become extremely important nectar sources (Safford 1991). High densities may be associated with mosaics of small plantations of exotic trees, where nest-predation may be low, interspersed with native vegetation for foraging (Safford 1997c). 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 mauritianus (Nichols et al. 2005). In recent decades pairs on the mainland have not generally fledged more than one offspring per nesting attempt and productivity was 7-17% during three study seasons (Nichols et al. 2005). In more recent study seasons (2005-2008) productivity has been higher, particularly on Ile aux Aigrettes, 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 eggs (R. Cole in litt. 2007).

Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):3.5
Movement patterns:Not a Migrant

Threats [top]

Major Threat(s): Zosterops 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 (C. Jones in litt. 2000, Nichols et al. 2005): 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 failure (Sørensen 2005). Fifty-six monitored nesting attempts in the Combo area in 2010/11 produced a total of only seven fledglings, but experimental poison grids were found to significantly improve nest success (Anon 2011).

Conservation Actions [top]

Conservation Actions: Conservation Actions 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 (Jones and Hartley 1995, R. Safford in litt. 1999). 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 monitored (R. Cole in litt. 2007). Between 2005-2008 an intensive management plan was 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 in December 2006 (R. Cole in litt. 2007). 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 strategy (R. Cole in litt. 2007). 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 birds (Safford and Jones 1998). A total of 38 individuals, all originating from wild nests, were released onto Ile aux Aigrettes between 2006 and 2008 (R. Cole in litt. 2007, G. Maggs in litt. 2010). The Ile aux Aigrettes sub-population is closely monitored and provided with supplementary food, and the first fledglings were produced in 2008 (G. Maggs in litt. 2010). In 2010, 14 fledglings were produced from five breeding pairs, and the total population currently stands at 25 individuals (G. Maggs in litt. 2010). Several individuals from rescued nests were hand-reared by a team from Chester Zoo, the Durrell Wildlife Conservation Trust and the Mauritian Wildlife Foundation (Sørensen 2005), but 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-eye (R. Cole in litt. 2007). Releases and nest rescues are now set to cease, and intensive research regarding habitat use, feeding ecology and nesting success will be carried out to highlight major limiting factors for the species and refine management techniques (G. Maggs in litt. 2010).

Conservation Actions Proposed
Continue population monitoring and ringing. Continue rehabilitation of native forest in appropriate areas to improve food sources for the species. Continue monitoring of accessible nests at Combo and Ile aux Aigrettes (Anon 2011). 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 controlled (Nichols et al. 2005). Initiate studies to investigate habitat requirements with view to developing habitat enrichment programmes and future species management techniques. Continue to search the Black River National Park and other suspected areas in Mauritius to identify new sub-populations (Anon 2011). Continue and extend the use of poison grids around nest sites to reduce rat predation (Anon 2011).

Citation: BirdLife International. 2012. Zosterops chloronothus. The IUCN Red List of Threatened Species 2012: e.T22714005A38095477. . Downloaded on 26 October 2016.
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