Taita White-eye Zosterops silvanus


Taxonomic note

Zosterops poliogastrus, Z. kaffensis, Z. kulalensis, Z. kikuyuensis, Z. silvanus, Z. eurycricotus, Z. mbuluensis and Z. winifredae (del Hoyo and Collar 2016) were previously lumped as Z. poliogastrus following Dowsett & Forbes-Watson (1993) and Sibley & Monroe (1990, 1993).

Taxonomic source(s)
del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A., Fishpool, L.D.C., Boesman, P. and Kirwan, G.M. 2016. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 2: Passerines. Lynx Edicions and BirdLife International, Barcelona, Spain and Cambridge, UK.

IUCN Red List criteria met and history
Red List criteria met
Critically Endangered Endangered Vulnerable
- - C2a(i)

Red List history
Year Category Criteria
2022 Vulnerable C2a(i)
2016 Endangered B1ab(i,ii,iii,v)
2012 Not Recognised
2008 Not Recognised
2006 Not Recognised
2004 Endangered
2000 Endangered
1994 Critically Endangered
1988 Not Recognised
Species attributes

Migratory status not a migrant Forest dependency medium
Land-mass type Land-mass type - continent
Average mass -

Estimate Data quality
Extent of Occurrence breeding/resident (km2) 870 medium
Area of Occupancy breeding/resident (km2) 116
Severely fragmented? no -
Population and trend
Value Data quality Derivation Year of estimate
Number of mature individuals 1200-9000,1830-4700 poor estimated 1999
Population trend decreasing inferred -
Number of subpopulations 3-10,3 - - -
Percentage in largest subpopulation 1-89 - - -
Generation length (years) 2.6 - - -

Population justification: Surveys in the late 1990s estimated a population of 7,123 (3,770-13,594) total individuals (Mulwa et al. 2007). This would roughly equate to 4,750 (2,500-9,100) mature individuals.

The species occurs in two of the three main blocks in the Taita Hills (the Dawida complex comprising eight occupied fragments and the Mbololo massif; no evidence of the species was found from the Sagala massif) and also on Mount Kasigau c. 50 km southeast (Mulwa et al. 2007). Mulwa et al. (2007) estimated numbers from within each block from fieldwork undertaken between November 1998 and September 1999; Dawida complex 878 individuals (95% confidence interval: 461-1,779), Mbololo 651 individuals (352-1,188) and Kasigau 5,594 individuals (2,957-10,627). These three areas are considered to represent three separate subpopulations, although there is the possibility that there may be further subdivision within the Dawida block.

Notably there is concern that the Kasigau population has since crashed (M. Adamjee in litt. 2022). The estimate was made at a time when the habitat was 'pristine' and the abundance of this species was exceptional, but the apparently insular nature of this population suggested fragility (Mulwa et al. 2007, R. Mulwa in litt. 2022). Subsequently the habitat has become at least partly degraded and in numerous recent visits abundance of Taita White-eye has been far lower, and a value of 1,000-1,500 individuals is considered a more accurate current range (M. Adamjee in litt. 2022). This revised value would suggest that no subpopulation is likely to hold more than 1,000 mature individuals, as well as indicating that at one site a rapid reduction is reported to have occurred. With degradation of the preferred montane forest habitat noted to be ongoing (Wakesa et al. 2020, R. Mulwa in litt. 2022) along with the noted reduction in abundance of the largest subpopulation, it is inferred that there is an ongoing decline in the number of mature individuals.

Trend justification: The population is inferred to be declining as a result of ongoing forest loss. Data from Global Forest Watch (2020) suggest that between 2009 and 2019, 1.2% of the forest in the species' range was lost. However, analysis by Wakesa et al. (2020) found that between 1973 and 2016, the larger forest blocks in the Taita Hills (Chawia, Fururu, Mbololo, Ngangao and Vuria) decreased by 23.2%. This roughly equates to a rate of 6% over 10 years. The direct rate of population decline is difficult to quantify as this species prefers edge habitats, however due to the restrictedness of the remaining habitat, the overall trend is declining.

Country/territory distribution
Country/Territory Presence Origin Resident Breeding Non-breeding Passage
Kenya extant native yes

Important Bird and Biodiversity Areas (IBA)
Country/Territory IBA Name
Kenya Taita Hills Forests

Habitats & altitude
Habitat (level 1) Habitat (level 2) Importance Occurrence
Forest Subtropical/Tropical Moist Montane major resident
Altitude 840 - 1725 m Occasional altitudinal limits  

Threats & impact
Threat (level 1) Threat (level 2) Impact and Stresses
Agriculture & aquaculture Annual & perennial non-timber crops - Small-holder farming Timing Scope Severity Impact
Ongoing Minority (<50%) Causing/Could cause fluctuations Low Impact: 5
Ecosystem degradation, Ecosystem conversion
Biological resource use Logging & wood harvesting - Unintentional effects: (subsistence/small scale) [harvest] Timing Scope Severity Impact
Ongoing Minority (<50%) Slow, Significant Declines Low Impact: 5
Ecosystem degradation, Ecosystem conversion

Recommended citation
BirdLife International (2023) Species factsheet: Zosterops silvanus. Downloaded from on 04/10/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from on 04/10/2023.