The mountain blackeye (Zosterops emiliae), sometimes referred to as the olive blackeye or simply black-eye, is a species of passerine bird in the family Zosteropidae. It is endemic to the highest mountains on the island of Borneo. It is known from both Malaysian states on the island, and four of the five Indonesian provinces, but has never been recorded in Brunei. Typically found at elevations above 1,800 m (5,900 ft), the mountain blackeye sometimes moves to lower altitudes during periods of drought. There are four subspecies, which show clinal variations in size and coloring. Birds in the north are largest, darkest, and proportionately longer-tailed, while those further south are smaller, paler, and proportionately shorter-tailed. Adults are dark olive-green with a sharply-pointed, bright yellow-orange bill and a small dark mask connecting black lores with a black eye-ring. The subspecies show varying amounts of yellow in their plumage, particularly on the face and underparts. Young birds resemble their parents, but have less brightly colored bills.

It feeds on insects, nectar, pollen, and small fruits, and is a major pollinator of several species of Rhododendron. It is also a minor partner in a symbiotic relationship with the pitcher-plant Nepenthes lowii. Little is known about its breeding ecology. Its nest is a shallow cup made of rootlets and lined with bits of moss. The female lays a single egg, and the nestling takes 14–15 days to fledge after hatching. The International Union for Conservation of Nature lists it as a species of least concern. Although its population has not been quantified, it is very common across much of its range.

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