Zosterops conspicillata hypolais Stresemann, Mitt. Zool. Mus. Berlin, 17, 1931, p. 227 (Yap); Mayr, Amer. Mus. Novit., no. 1269, 1944, p. 7 (Yap); idem, Birds Southwest Pacific, 1945, p. 299 (Yap).
Zosterops hypolais Hand-list Japanese Birds, rev., 1932, p. 173 (Yap).
Geographic range.—Micronesia: Caroline Islands—Yap.
Characters.—According to Hartlaub and Finsch (1872:95), "Upper parts of a pale greyish green, throat and under tail-coverts a pure but very pale whitish-yellow; breast and abdomen of a mixed pale grey and pale yellow; wing- and tail-feathers pale blackish, margined with greenish colour of the back; under wing-coverts and inner margins of remiges white; eye-ring indistinct; beak fuscous, the under mandible paler, except at the tip; feet plumbeous."
Remarks.—No specimen has been examined by me. I am following Stresemann (1931:227) in placing the Bridled White-eye at Yap as a subspecies of Z. conspicillata. This is one arrangement; the committee who prepared the Hand-list of Japanese Birds (1942:192) treat this bird as a separate species. The Japanese probably have more specimens of this bird than anyone else and may be in a better position to judge its taxonomic status. Specimens of this white-eye were taken by Fisher in 1946 at Yap. His report (soon to be published) may throw additional light on the degree of distinctness of Z. c. hypolais. On the basis of published descriptions it is evident that Z. c. hypolais has a few characters in common with other members of the species.
Evolutionary history of Zosterops conspicillata.—The small olive-green and yellow white-eyes of Micronesia have been considered as belonging to several species by authors in the past. As late as 1930, Mathews (1930; 700, 706) placed them in four species. Stresemann (1931a: 227) put them all in the species Z. conspicillata, an arrangement which is being followed in this report. It is evident, however, that these subspecies of Z. conspicillata can be associated into three groups. The author (1948:73) states that Z. c. conspicillata and Z. c. saypani have pale chins and throats, light fronto-loral bands, blackish coloring at the bend of the wings and broad, white orbital rings. Another group, Z. c. rotensis, Z. c. semperi, Z. c. owstoni, and Z. c. takatsukasai, have bright yellow chins and throats, matching the rest of the underparts, obscure fronto-loral bands, which are narrowly tinged with yellow, yellowish coloring at the bend of the wings, and narrow, white orbital rings. Z. c. hypolais apparently falls into a third group by itself, as indicated by the published descriptions. There is apparently some variation in the color of the eyes of these subspecies; they may be either whitish or chestnut in color. The data are insufficient to determine the significance of this color character.
Z. conspicillata is restricted to Micronesia and appears to have little close relationship to other species of the genus. Z. conspicillata shows little affinity to white-eyes to the north and northwest of Micronesia belonging to the species Z. japonica, of which representatives are found in the Bonin and Volcano islands. Z. conspicillata shows greater affinity to species found to the west and to the south of Micronesia.
It may have colonized Micronesia from the south or southeast (Polynesia), even though the species is absent at Kusaie; however, Z. conspicillata shows more relationships to species now living to the westward and the southwestward, and it probably invaded Micronesia from some place in that direction. Z. conspicillata differs from species found in Melanesia and Malaysia chiefly in color of the forehead, lores, fronto-loral band, crown, nape, breast, abdomen, orbital ring, and bill. Also there are differences in the breadth of the orbital ring.
Z. conspicillata shows evidence of relationships with Z. nigrorum of the Philippines and Z. montanus of the Philippines and other parts of Malaysia. Z. nigrorum resembles Z. c. semperi of Palau in size, but is brighter yellow-green above with a darker and less curved bill and brighter underparts. The fronto-loral band and the lores are colored the same in Z. nigrorum and Z. c. semperi. Z. montanus resembles Z. conspicillata especially in size and in shape of the bill. Z. lutea intermedia of the Makassar area shows some affinity to Z. conspicillata, although the bill is heavier. The Micronesia species also bears a close resemblance to Z. griseotincta of the Papuan region. This is especially true of Z. c. takatsukasai at Ponapé; however, Z. griseotincta has a heavier and larger bill. Z. lateralis from southern Melanesia and Australia is not very different from Z. conspicillata aside from its grayish and brownish coloring.