Data Zone
Justification of Red List category
This species has a very small population size restricted to a single subpopulation. There is much uncertainty surrounding the species due to a lack of recent records, however available data are indicative of a decline in at least one locality since 1984 and this is likely to be continuing given the likely ongoing threats. It is therefore assessed as Endangered.
Population justification
This species has always been regarded as uncommon in its tiny range: one scientist who spent more than 14 months in the Chuuk Islands failed to see it entirely, and it may be largely restricted to Tol with only localised populations on the other islands (Brandt 1962). The population has not been robustly estimated since 1984 when bird surveys (Engbring et al. 1990) found it locally common on Tol South (382 individuals) and rare on Onei (19 individuals), Paata (32 individuals) and Polle (93 individuals). In total, this estimate of 530 individuals may roughly equate to c.350 mature individuals. There is no more recent population estimate; many of these sites have not been searched in recent years, with one record on Paata in 2007 and all observations since 2010 concentrated on Mt Winipot, Tol South (eBird 2023, M. O'Brien in litt. 2023). In the absence of more recent and complete data, the population is tentatively placed in the range 300-400 mature individuals. However, there is evidence that the species has likely declined since the 1984 estimate (see Population trend), and an up to date quantification of the population size is urgently required.
Trend justification
There is considerable concern and uncertainty surrounding this species, with no reliable monitoring data and no recent on-ground access to the population being possible. However, the species is dependent on old-growth stands of native forest which is subject to deforestation and contains non-native species (Engbring et al. 1990, SPREP 2001), has declined from its historic distribution and may continue to be under threat from population pressures (R. Davis in litt. 2023). In 1984 bird surveys (Engbring et al. 1990) found the species to be locally common on Tol South (with an estimated 382 individuals in total) and rare on Onei (19 individuals), Paata (32 individuals) and Polle (93 individuals). Many of these sites have not been searched in recent years, with all observations since 2010 concentrated on Mt Winipot, Tol South (eBird 2023, M. O'Brien in litt. 2023). Although methods vary, the number of birds seen during visits to Mt Winipot since 2010 suggest a decline from 1984 estimates (eBird 2023, M. O'Brien in litt. 2023). Additionally, no calls have been extracted from acoustic surveys carried out on Onei in 2022, and difficulties regarding access permissions has prevented surveys of the other Faichuk islands (M. O'Brien in litt. 2023). Precautionarily therefore, the population is inferred to be declining overall.
Rukia ruki has a tiny occupied range being recorded from four tiny islands in the Faichuk Group of the Chuuk lagoon, Federated States of Micronesia: Tol South, Onei, Pata and Polle (Engbring et al. 1990).
The species has been recorded in old and secondary-growth stands of native forest, particularly the rich and well-developed forest above 400 m on Mt Winipot (Tol South), where fig trees Ficus spp., native palms Clinostigma spp., Parinarium, Randia and the endemic poison tree Semecarpus kraemeri predominate, the latter possibly playing an important ecological role in the species's survival (Engbring et al. 1990, C. Collins in litt. 2007). It is also found in areas of native trees mixed with plantations (Engbring et al. 1990, D. Scott in litt. 2011), but densities are much lower (J. Lepson in litt. 1999). It feeds by foraging for insects in the foliage (Engbring et al. 1990). It is territorial; breeding has been observed in April, and the only recorded nest was in a S. kraemeri tree, supporting the premise that a commensal and possibly mutual relationship exists between the two species (Pyle and Engbring 1988).
Deforestation has occurred across much of Chuuk Archipelago, but forests on the plateau of Tol South at least are old-growth and relatively undisturbed overall and superstitious beliefs apparently inhibit many islanders from trying to visit the plateau (C. Collins in litt. 2011). Previous observations from Tol South suggest that only subsistence-level timber extraction is now occurring, owing to the topography of the island and areas of difficult terrain (C. Collins in litt. 2011, D. Scott in litt. 2011). However, there is considerable concern surrounding this species, with no recent on-ground access to the population being possible. The species is dependent on old-growth stands of native forest (Engbring et al. 1990) and conversion to agriculture has been considered a threat (SPREP 2001). The species may continue to be under threat from the expanding human population, with degradation of many other areas of habitat in Chuuk ongoing due to population pressures (van Balen 2020, R. Davis in litt. 2023). Additionally, acoustic recordings from Onei suggest that human intrusion may be high in some parts of the range (M. O'Brien in litt. 2023). The extent and spread of invasive species including plants, rats and cats within the range is also a concern, though the impacts of these are largely unknown (Brandt 1962, Space et al. 2000; SPREP 2000, 2001; M. O'Brien in litt. 2023). The introduction of Brown Tree Snake Boiga irregularis has been considered a possibility, which has caused the extirpation and extinction of birds on Guam (Engbring et al. 1990), although this threat is considered unlikely and its impacts on this species remain unknown. The species is potentially threatened by extreme storm events given its extremely restricted range, a threat that could potentially be exacerbated by climate change.
Conservation Actions Underway
No targeted actions for this species are known.
14 cm. Medium-sized, all-dark, warbler-like bird. Uniform dark-brown with black bill, orange legs and conspicuous white "teardrop" below the eye. Voice Lively song, lilting warble very similar to song of Golden White-eye Cleptornis marchei of the Marianas. Hints Mostly found in remnant native forest, but ranges into disturbed areas nearby.
Text account compilers
Berryman, A., Vine, J.
Contributors
Collins, C., Davis, R., Dutson, G., Lepson, J., O'Brien, M. & Scott, D.
Recommended citation
BirdLife International (2024) Species factsheet: Teardrop White-eye Rukia ruki. Downloaded from
https://datazone.birdlife.org/species/factsheet/teardrop-white-eye-rukia-ruki on 22/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/12/2024.