Physical characteristics

White-eyes have somewhat rounded wings with only nine functional primaries (the outermost primary is much reduced), and a brush-tipped tongue, quadrifid and fimbriated both at the sides and at the tip, showing a high degree of specialization for nectar feeding. In nearly all species, a white eye-ring appears soon after fledging, formed of minute silky white feathers. The ring is interrupted usually by the blackish lore. Iris color ranges from gray to brown and does not relate to age, sex, or race. The apposition of melanins and yellow carotenoids produces various shades of yellow-green, depending on the amount and distribution of these pigments and the structure of the feathers. The upperparts are green to greenish yellow, with gray upperback in some species, and the underparts are yellowish from throat to undertail coverts in some species or grayish to white in others. Flank color varies from light gray to dark brown. There are no seasonal changes in plumage color and the sexes are similar, though males tend to be larger and more brightly colored or darker than females in colder parts of Australia and New Zealand (Z. lateralis). Their short, thin bill is blackish, slightly decurved, and sharply pointed. The legs are grayish to brownish, the

Silvereye (Zosterops lateralis) at its nest in an orange tree. (Photo by Peter Slater. Photo Researchers, Inc. Reproduced by permission.)

first-year birds having darker colors and young fledglings and old birds having a pinkish color. Older birds (older than 5 years) molt into longer wing and tail feathers.

Continental species typically have short wings (2.2-2.6 in [55-65 mm]) and weigh 0.3-0.5 oz (9-15 g), with a cline following Bergmann's rule (larger in higher latitudes), but the derived island species and races tend to increase bill, leg, and body sizes. For example, in the eastern races of silvereyes (Z. lateralis) in Australia and New Zealand, a comparison between local populations indicates that the South Island population of New Zealand is the largest and the northern Australian population the smallest. At northern sites the winter populations are diluted by large southern migrants, except on wooded islands of southern Great Barrier Reef, where the Capricorn race (Z. lateralis chlorocephalus) is resident and much larger (body weight 0.49-0.53 oz [14-15 g]) than the mainland races (0.3 oz [10 g]) that migrate. Another genus of this family, Lophozosterops, with six species, mostly mountain birds of Indonesian and Philippine islands (Java, Bali, Sumbawa, Flores, Sulawesi, Seram, and Mindanao), contains not only very large species (wing greater than 2.8 in [70 mm]) but also atypical forms. They have a gray or brown crown, which is often striped or has small white spots. One species, Lophozos-terops dohertyi, has a crest. In the giant white-eye, Megazos-terops palauensis, of Palau island, the wing length reaches 3.3 in (85 mm) and weighs up to 1.1 oz (31 g). In the mountain blackeye, Chlorocharis emiliae, of northern Borneo and Bonin white-eye, the feathers around the eye are black.

0 0

Post a comment