Ecology and Evolution of the Sympatric Mascarene White-Eyes, Zosterops borbonica and Zosterops olivacea

Abstract

THE Zosteropidae, or white-eyes, are a small paleotropical group of generalized passerines that have colonized more oceanic islands than any other passerine family (Moreau, 1964). While two species of Zosterops rarely coexist in mainland avifaunas, multiple invasions of small islands have resulted in several cases of bona fide sympatry. One such case involves the endemic Mascarene white-eyes, Z. borbonica and Z. olivacea, which are sympatric on Mauritius and Reunion Islands in the western Indian Ocean. Whereas niche expansion in a reduced competitive environment seems to be frequent in island coloinists (Mac Arthur and Wilson, 1967; Keast, 1968), studies of the Mascarene white-eyes, here reported, suggest that the first white-eye to colonize the Mascarene islands became more specialized, rather than more generalized, in the absence of competitors. A second successful colonization by a generalized white-eye and subsequent sustained coexistence of the two species was apparently facilitated by the specialization of the first arrival.