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A post-breeding flock of New Zealand Dotterels was monitored for 3.5 years at a site on the east coast of Northland, New Zealand. The pattern of flocking and dispersal was the same each year; the flock began to form in January and was at peak numbers in February and March. Birds began to return to their breeding grounds in late March, and two-thirds of those that bred away from the flock site had left by the end of April. Individual colour- banding showed a very high degree of breeding-site and flock-site fidelity. All the adults in the flock bred within a 16 km radius (the central study area) and none was found outside this area during the study. All adults in the central study area visited the flock each year; however, at two other localities in the greater study area a few birds were entirely sedentary on their breeding grounds and did not visit a flock. Breeding territories of birds resident at the flock site changed little between seasons. Unlike many migratory members of the genus Charadrius, NZ Dotterels of the northern population showed very high mate-retention from one season to the next, with both members of a pair usually occupying their territory for much of the year.