Results of 3499 10 min counts and other shipboard observations made during 27 voyages between Reunion, Mauritius and the subantarctic showed pronounced seasonal variation in the distribution of Barau’s Petrel. Rare south of 20°S in July – August, it appeared in numbers off Reunion by September, and remained mostly confined to tropical waters north of 25°S until November. From December to March, the range of this tropical breeding petrel expanded far south into subtropical waters, with a major foraging zone 1100-1400 km from Reunion. The southernmost record was beyond 41°S. The summer population in the SW Indian Ocean is estimated at 9000-15000 individuals. In tropical waters, Barau’s Petrels feed almost exclusively in multispecies flocks and apparently mostly on schooling fish. Topics of discussion include population trends, migration, foraging radius, and distribution in relation to breeding status and food resources.