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Range DescriptionHydrobates tristrami breeds in the Hawaiian archipelago (USA), on Nihoa (2,000-3,000 pairs), Necker, French Frigate Shoals (max 280 pairs), Laysan (500-2,500 pairs), Pearl and Hermes Reef (1,000-2,000 pairs), and may also breed on Midway, Lisianski and Kure (Rauzon et al. 1985, Harrison 1990, Enticott and Tipling 1997, Baker et al. 1997, McClelland et al. 2008). It also breeds on a few small predator-free islets of the Bonin and Izu Islands, Japan (McClelland et al. 2008), including six islands in the Bonin group, three of which were newly identified as part of a survey that concluded in 2005. They were not detected on the Volcano Islands, where the species bred before WWII (Chiba et al. 2007). These estimates suggest that the world population is no greater than 30,000 birds, including 10,000 pairs (Brooke 2004). This species is difficult to monitor due to its high sensitivity to human disturbance during the incubation phase (Marks and Leasure 1992) and due to its habit of breeding in the winter months when access to its remote breeding colonies is more difficult. Little is known about its post-breeding dispersal, but some move north to the seas east of Japan (Carboneras 1992a, Enticott and Tipling 1997).