SummarySeabirds in Madang Province waters were surveyed during 40 small-boat trips from 20 September to 27 November 1989. At least 11 579 individuals of 21 species were identified. None nested near Madang. The seasonal status, abundance, habitat distribution and day-roosting habits are reported for each species. Heinroth's ShearwaterPuffinus heinrothiand Grey-backed TernSterna lunataare documented for the first time in mainland New Guinea waters, but at least the former is believed to be regular near Madang. Ten species of terns represented 93.7% of all seabirds. Seven boreal migrant species including Common TernS. hirundo(69.1% of all identified seabirds) and Little Tern S.albifrons(6.0%) contributed 76.9% of the total. Twelve tropical species made up nearly all of the remainder. Total abundance was greatest in the inshore and harbour zones, but species diversity increased with distance offshore. Only six species (all terns) were seen roosting at only two sites on land or on a channel marker. Terns and boobies rested on any suitable flotsam, from coconuts to huge offshore rafts that included trees. Foraging distributions of these birds appeared to be influenced by the ephemeral distributions of both flotsam and feeding tuna schools. In the absence of flotsam, terns waiting for feeding tuna to resurface often settled on the water in dense flocks.