During a prolonged drought in 1976-78 on the island of Daphne Major in the Galapagos Archipelago, (a) the population size of finches (Geospiza fortis) decreased, due to (b) the decline in seed supply, during which time (c) the size & hardness of seeds increased. As a result, (d) the average size of finches increased, because only larger birds that could handle such seeds efficiently survived.