SummaryThis paper sets out the results of fairly regular observation ofOreotrochilus chimborazoon Mt Cotopaxi between 1964 and 1967.The species is found between 13,000 and 15,000 ft in a small area just south of the Equator where it nests on cliffs. Climate, terrain, food and nesting are described. Breeding continues throughout the year. Particular attention is given to the importance of nesting sites in this harsh climate and the consequent tendency towards colonial* nesting in favoured spots. The high degree of segregation between the sexes is also considered.A brief account is given of theO. chimborazopopulation in the Guamani pass on the rim of the Amazon basin, where climate and terrain have produced some differences in breeding habits.