Bird numbers and habitat preferences were noted regularly for 3 years on the delta of the Cass River, Lake Tekapo. Species counted were an oystercatcher, three plovers, two stilts, two gulls and two terns. Most species left the area after breeding and numbers were highest during spring. The river mouth and lake shore were most used in late winter and early spring before all species moved away to forage and nest in other habitats, particularly on the shingle riverbed and adjacent river terraces. Seasonal patterns were modified by rapid artificial changes in lake level, by excessive river flooding, and by snow-storms.