In 1996, a study to locate and describe breeding sites, estimate pair densities and document brood movements of Harlequin Ducks (Histrionicus histrionicus) was conducted on selected rivers of the Gaspé Peninsula, Québec. Pair densities on the Port-Daniel, Sainte-Anne and Madeleine River systems were low: 0.32, 0.10 and 0.06 pairs/km, respectively. Six VHF radiotransmitters were implanted in nesting females on the Port-Daniel and Sainte-Anne Rivers. Two successful nests were located on cliff ledges and one unsuccessful nest was located on the ground on an island. These nests represented the first recorded for the eastern North American Harlequin Duck population. Of the marked hens, two successfully hatched ducklings. One was followed for a month until the female was killed by a Great Horned Owl (Bubo virginianus). The brood used a six km stretch of the Sainte-Anne River during that period. The other brood was tracked for two months and concentrated its activities along a three km stretch of the Port-Daniel River. The female was located in coastal waters near Newport on 24 August 1996. Two of the marked females from the Port-Daniel River and one from the Sainte-Anne River migrated to Bonaventure Island, where they likely molted. A female captured on the Port-Daniel River was killed by a Red-tailed Hawk (Buteo jamaicencis) before its nesting status was confirmed. A female from the Port-Daniel River was located at the Sally islands, Maine, on 5 December 1996. The study confirmed the importance of the Gaspé Peninsula Rivers for breeding Harlequin Ducks and the use of adjacent coastal molting sites by postbreeding females. It also established a link with the major Maine wintering area.