Bioko Speirops Zosterops brunneus


Justification of Red List category
This species is classified as Vulnerable on account of its very small range. Although it is apparently currently secure, it is inherently at risk, especially from any loss of its very restricted habitat.

Population justification
The population size is preliminarily estimated to fall into the band 10,000-19,999 individuals. This equates to 6,667-13,333 mature individuals, rounded here to 6,000-15,000 mature individuals.

Trend justification
The species's population is suspected to be stable because access to its habitat is restricted and no immediate threats are known.

Distribution and population

Speirops brunneus is known only from Pico Basilé (formerly de Santa Isabel), on Bioko, Equatorial Guinea. It is possible that it could also occur on the nearby (much smaller) Caldera de Luba (Pérez del Val 1996). Surveys in the early 1990s found the species to be common within its range (Pérez del Val 1996).


It is found on the higher slopes (above 1,900 m), where it inhabits lichen forest and montane heathland. It occurs in groups of four to five, searching for insects amongst the lower branches of Hypericum lanceolatum trees and also takes fruit and seeds (Pérez del Val 1996).


The main threat could be fires set by hunters, but no evidence of this was seen in 1996 (R. A. Cheke in litt. 1999). A visit to the area in 1996 confirmed that habitat at Pico Basilé remained intact (R. A. Cheke in litt. 1999). Reports up to 2005 indicate that the accelerated rates of deforestation occurring on the island had not affected Pico Basilé (R. Cheke in litt. 2007). Images of Caldera da Luba and the southern forests taken in 2005 do not indicate any encroachment in these areas (R. Cheke in litt. 2007).

Conservation actions

Conservation Actions Underway
Pico Basilé is a restricted area as the radio mast at the summit of the mountain has been designated a security zone (R. A. Cheke in litt. 1999). The Bioko Conservation Project has initiated regular research in the forests of the island and increased its international recognition (

Conservation Actions Proposed
Conduct a baseline survey to obtain a population estimate, map its range more accurately and check for its presence on Caldera de Luba. Monitor the species periodically to ascertain any population and/or range trend. Protect habitat on Caldera da Luba if the species is found there.


12 cm. Small, all-brown, warbler-like bird. Darker brown upperparts and head, paler on belly with greyish throat. Greyish-blue bill and legs. Voice Long, trilling trrrrrrrruuuuu or rapid tric tric tric.


Text account compilers
Ekstrom, J., Pilgrim, J., Shutes, S., Symes, A., Taylor, J. & Westrip, J.

Cheke, R.

Recommended citation
BirdLife International (2023) Species factsheet: Zosterops brunneus. Downloaded from on 25/09/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from on 25/09/2023.