Systematics

The Bridled White-eye was apparently reported from Tinian Island in 1742, when a beautiful little green bird from there was described in journals of the H.M.S. Centurion (20 Barratt, G. (1988). H.M.S. Centurion at Tinian 1742: the ethnographic and historic records. Micronesian Archaeological Survey Report 26. Close ). The Guam population was first named Dicaeum conspicillatum (21 von Kittlitz, F. H. (1832). Kupfertafeln zur Naturgeschichte der Vögel. Part 1. Frankfurt am Main, Germany. [In German]. Close , 22 von Kittlitz, F. H. (1835). Über einige vögel von Chili, beobachtet im März und anfang April 1827 Fortsetzung. Mémoires Présentés a L’académie Impériale des Sciences de St. Pétersbourg par Divers Savans 1:465–472. Close , 23 Lutké, F. 1835−1836. Voyage autour de monde, exécuté par ordre de sa majesté l’empereur Nicolas 1, sur la corvette Le Séniaville, dans les années 1826, 1827, 1828, et 1829. Partie historique avec un atlas, lithographié d’aprés les dessins originaux d’Alexandre Postels et du Baron Kittlitz, volume 1−3. Didot, Paris. Close ). It was then assigned to Zosterops conspicillatum by Bonaparte (1850−1857), listed as Zosterops conspicillata by Reichenbach (24 Reichenbach, H. G. L. (1852). Avium systema naturale: das natürliche system der vögel. Expedition der vollständigsten naturgeschichte, 1850. Dresden and Leipzig, Germany. Close ), and listed as Zosterops conspicillatus by Momiyama (25 Momiyama, T. T. (1922). Birds of Micronesia. Ornithological Society of Japan, Tokyo, Japan. Close ). The subspecies conspicillata was first recognized by Stresemann (26 Stresemann, E. (1931). Die Zosteropiden der Indo-australischen Region. Mitt. Zool. Mus. Berlin 17(2): 201-238. In German. Close ). The subspecies saypani was distinguished by Dubois (27 Dubois, A. (1899-1902). Synopsis avium: nouveau manuel d’ornithologie. Première Partie. H. Lamertin, Brussles, France. Close ), although it was listed as a separate species, Zosterops saipani, by Mathews (28 Mathews, G. M. (1930). Systema Avium Australasianarum. A Systematic List of the Birds of Australia. Part 2. British Ornithologists’ Union, London, UK. Close ). More recently, subspecies saypani also was considered a distinct species (29 del Hoyo, J., and N. J. Collar (2016). Handbook of the Birds of the World and BirdLife International Illustrated Checklist of the Birds of the World. Volume 2. Lynx Edicions, Barcelona, Spain. Close , 30 Pratt, H. D. (2010). Revisiting species and subspecies of island birds for a better assessment of biodiversity. Ornithological Monographs 67: 79–89. Close ). However, considering the estimated short period of genetic divergence of the Guam and Saipan populations, ~10,000 years, these are generally treated as conspecific (31 Stattersfield, A. J., and D. R. Capper, Editors (2000). Threatened Birds of the World. Lynx Edicions, Barcelona, Spain. Close , 32 Dickinson, E. C., Editor (2003). The Howard and Moore Complete Checklist of the Birds of the World. 3rd edition. Christopher Helm, London, UK. Close ). The Rota White-eye (Zosterops rotensis), the Caroline Islands White-eye (Zosterops semperi), and the Plain White-eye (Zosterops hypolais) were formerly considered conspecific with the Bridled White-eye (1 Baker, R. H. (1951). The avifauna of Micronesia. Its origin, evolution, and distribution. University of Kansas Publications, Museum of Natural History 3(1):1–359. Close ), although DNA studies indicate that the Bridled White-eye is a distinct species from them (33 Slikas, B., I. B. Jones, S. R. Derrickson, and R. C. Fleischer (2000). Phylogenetic relationships of Micronesian white-eyes based on mitochondrial sequence data. The Auk 117(2):355–365. Close , 34 Oliveros, C. H., M. J. Andersen, and R. G. Moyle (2021). A phylogeny of white-eyes based on ultraconserved elements. Molecular Phylogenetics and Evolution 164:107273. Close )

The plumage of the Bridled White-eye subspecies saypani is similar to the subspecies conspicillatus, but the fronto-loral band is more greenish yellow, the auriculars are olivaceous rather than grayish, the crown is greenish rather than gray, the orbital ring is narrower, the upperparts are brighter olive, the underparts are paler yellowish white, and the bill is darker. Birds from Saipan closely resemble birds from Tinian and Aguiguan, but Saipan birds may have upperparts that are slightly brighter and underparts slightly more yellow (1 Baker, R. H. (1951). The avifauna of Micronesia. Its origin, evolution, and distribution. University of Kansas Publications, Museum of Natural History 3(1):1–359. Close , 35 Pratt, H. D., P. L. Bruner, and D. G. Berrett (1987). A Field Guide to the Birds of Hawaii and the Tropical Pacific. Princeton University Press, Princeton, NJ, USA. Close ). Marshall (2 Marshall, J. T. (1949). The endemic avifauna of Saipan, Tinian, Guam and Palau. Condor 51(5):200–221. Close and 36 Engbring, J., Ramsey, F.L. and Wildman, V.J. (1986). Micronesian Forest Bird Survey, 1982: Saipan, Tinian, Agiguan, and Rota. US Fish & Wildlife Service Report, Honolulu, Hawaii. Close ) could find no difference between populations. In subspecies conspicillatus, the upper mandible is more grayish, and the iris is described as light umber, whereas in subspecies saypani, it is described as chestnut (1 Baker, R. H. (1951). The avifauna of Micronesia. Its origin, evolution, and distribution. University of Kansas Publications, Museum of Natural History 3(1):1–359. Close ). Discriminant function analysis, albeit with small samples, suggested that Aguiguan birds were larger than the birds of Saipan (19 Craig, R. J., A. Ellis, and R. Kaipat (1993). Genetic isolation and the comparative morphology of small passerines on Aguiguan and Saipan. Proceedings, Marianas Research Symposium 1:22−25. Close ). Guam birds were larger than Saipan and Tinian birds (1 Baker, R. H. (1951). The avifauna of Micronesia. Its origin, evolution, and distribution. University of Kansas Publications, Museum of Natural History 3(1):1–359. Close , 35 Pratt, H. D., P. L. Bruner, and D. G. Berrett (1987). A Field Guide to the Birds of Hawaii and the Tropical Pacific. Princeton University Press, Princeton, NJ, USA. Close ).

This species belongs to a large clade of ~40 Indo-Pacific Zosterops species (37 Fjeldså, J., Ericson, P.G.P. and Christidis, L., editors. 2020. The largest avian radiation: the evolution of perching birds, or the order Passeriformes. Lynx Edicions, Barcelona, Spain. Close ). DNA studies demonstrate that the Bridled White-eye is sister to a clade formed by the Dusky White-eye (Zosterops finschii) and the Yap White-eye (Zosterops oleagineus) (34 Oliveros, C. H., M. J. Andersen, and R. G. Moyle (2021). A phylogeny of white-eyes based on ultraconserved elements. Molecular Phylogenetics and Evolution 164:107273. Close ). Its relationship to the Rota White-eye is not determined in this study, although Slikas et al. (33 Slikas, B., I. B. Jones, S. R. Derrickson, and R. C. Fleischer (2000). Phylogenetic relationships of Micronesian white-eyes based on mitochondrial sequence data. The Auk 117(2):355–365. Close ) examined DNA of the Bridled White-eye, the Caroline Islands White-eye, the Plain White-eye, the Yap White-eye (previously Rukia oleaginea), and the Golden White-eye (Cleptornis marchei) and found substantial genetic divergence (5.7‒7.3%) among the first three of these, which were formerly treated as a single species, as well as 6.5 ± 1.7% divergence between the Rota White-eye and the previously considered conspecific populations on Guam, Tinian and Saipan.

Subfossils of Zosterops bones, all identified as the Bridled White-eye, have been uncovered on Rota, Aguiguan, and Tinian (38 Steadman, D. W. (1999). The prehistory of vertebrates, especially birds, on Tinian, Aguiguan, and Rota, Northern Mariana Islands. Micronesica 31(2):319−345. Close ).