Reunion Gray White-eye Zosterops borbonicus Scientific name definitions

10·7–11·4 cm; male 6·8–10 g, female 7·3–11·1 g. Distinctive white-eye with white rump, no eyering; characteristically cocks the tail. Adult has crown, back and upperwing-coverts slaty grey or brownish, rump and uppertail-coverts white; lores dusky, variable narrow whitish line above, ear-coverts paler ashy than back; flight-feathers blackish, narrowly edged slaty, a little more hoary on primaries, tail feathers blackish, edged grey on outer webs, edged whitish on inner webs; cheeks and chin hoary white, throat to breast ashy grey, abdomen whitish with slight ashy tinge, body-sides and flanks ashy grey, thighs and vent white with slight ashy tinge, underwing-coverts and axillaries white; obvious pale stripe running down sides of puffed-out breast and flanks (gives unusual “epaulette” effect); iris bright hazel to chestnut or dull brown; bill dull lead colour, base of mandible paler; legs dull lead. Polymorphic: brown-backed with grey head in N & E, grey-headed with brown nape in S, and brown-headed and brown-backed in W & C parts of island; and others, with grey back and grey head, which rarely occur below 700 m but increase to 65–100% of population above 1300 m in N & E, and rarely below 1200 m in W; within and between each morph a complete range of colours, but with low proportion of intermediates; apart from plumage differences, morphs differ slightly also in weight and bill length (often related to sex and altitude), and grey morphs slightly larger than brown morphs, also other biometric differences recorded. Distinguished from sympatric Z. olivaceus and Z. chloronothos mainly by paler appearance, much greyer (not olive-green) plumage, and white rump. Sexes identical. Juvenile is like adult, but young fledgling has yellow gape and pinkish legs.

Introduced, unsuccessfully, to Île Sainte-Marie (off NE Madagascar) and Nosy Be (off NW Madagascar) in 19th century (4 Cheke, A. (2009). Was Mascarene Grey White-eye Zosterops borbonicus introduced to Madagascar? Bull. Brit. Orn. Club. 129(2): 104–108. Close ).

Reunion.

Scrub-forest, highland heath, evergreen forest, pine (Pinus) and casuarina (Casuarina) forest, gardens, natural forest at higher altitudes, to 2800 m; also seasonally in exotic vegetation at lower elevations. Has adapted to man-made forest-like habitats, such as orchards, timbered gardens and plantations, also secondary forest, but absent from sparsely vegetated natural habitats, and cane fields, geranium fields, sparse dry thorn-scrub etc.

Resident. The colour morphs appear to reflect unusually low levels of historical and contemporary gene flow among populations, derived from an extremely reduced propensity to disperse (5 Bertrand, J.A.M., Bourgeois, Y.X.C., Delahaie, B., Duval, T., García-Jiménez, R., Cornuault, J., Heeb, P., Milá, B., Pujol, B. and Thébaud, C. (2014). Extremely reduced dispersal and gene flow in an island bird. Heredity. 112: 190–196. Close ). Reports of some movement up and down 1000-m hills to visit flowering Sophora plants.

Primarily insectivorous ; also fruits and nectar. Insects include especially Hemiptera (whiteflies), grasshoppers and crickets (Orthoptera), dragonflies (Odonata), beetles, caterpillars and small butterflies (Lepidoptera). Once a tiny snail. Fruits, e.g. Aphloia theiformis at high altitudes (> 1500 m), also exotic Lantana camara, Schinus terebenthifolius, with a total of 15 species recorded. Nectar (taken by probing and sometimes puncturing corolla base) mainly from the introduced species Lantana camara, bottlebrush (Callistemon citrinus) and rose-apple (Syzygium jambos), but also native species e.g. Dombeya spp., Hypericum lanceolatum, Sophora denudata, Gaertnera vaginata, but a total of at least 24 species recorded; sweet sap oozing from trees (Claoxylon glandulosum, Acacia sp.) also taken. More fruits eaten in winter (Jun–Jul), whereas fruits rarely eaten at high altitudes in summer; above 2000 m buds of Philippia montana eaten where fruit-bearing plants absent, and when insects scarce (in winter). Forages throughout year in noisy parties of 4–10 individuals, sometimes up to 20 and exceptionally more than 200 birds; these flocks are occasionally joined by Mascarene Paradise-flycatcher (Terpsiphone bourbonnensis) and much more rarely by Z. olivaceus. Insects obtained by gleaning from foliage, by foraging among flowers , along twigs, on bark, probing in rotten wood, on the ground; aerial flycatching reported.

Song an elaborate loud warble, which intersperses flocking and contact calls, and sometimes contains mimicry of other birds, runs up and down scale and lasts between 10 and 30 seconds, e.g. “tuutreetertreetruuterrtree…”, but is sometimes much quieter and shorter (lasting just 1–3 seconds), a twittering “trissercristweeterrissterter”, recalling a sunbird; also an assemblage of sweet warbled phrases, “chip” notes, sputters and squeaks reminiscent of a catbird (Dumetella). Gives a soft twittering prior to arriving at roost. Calls given by day include “plee plee plee” as contact; also varied “chee chee chee”, plaintive “eeee” or double “eeee-eee” while feeding or as contact between flock members.

Sept–Dec, occasionally to Feb, and adults feeding young observed in Aug; peak probably Oct–Nov. Helpers feeding young reported; nests sometimes in loose semi-colonial groups, no territoriality or nest defence, but breeding units reported as holding very small (c. 1 ha) territory. Striking white axillaries and rump important in courtship display. Nest a small delicate cup (external diameter 60–65 mm, internal diameter 45–50 mm, height 45–52 mm, depth 45 mm) of fine stems , covered in green moss when in foliage (e.g. casuarina branchlets), or with grey-white material (possibly lichen), and sometimes with dead leaves in more exposed areas, attached to twigs at 1–5 m in tree (e.g. Erica/Philippia, Hypericum lanceolatum). Clutch 2–3 (occasionally four) eggs, pale blue, size 17–19 mm × 13–14 mm; incubation period 10–12 days; no information on fledging period.

Not globally threatened (Least Concern). Restricted-range species: present in Réunion EBA. Common; population estimated at 556,000 individuals in 1967 and subsequently at 465,000 birds in early 1980s; although white-eyes have not suffered from habitat modification by humans, the balance of polymorphism on the island undoubtedly has been affected. In 1970s, one observer suggested that population might have declined by as much as 80% during his lifetime. More recently, in Apr 2011, a study at 2000–2400 m on the Piton de La Fournaise volcano reported an estimated density of 5·17 birds ha, suggesting that highland areas of Réunion might support as few as 45,000 individuals; highest densities (11·4 birds/ha) reported in lowland forest. Main predator is Madagascar Marsh-harrier (Circus maillardi). Avian malaria may limit the distribution of white-eyes outside undisturbed forest.