Synchronous Eruptions of Boreal Seed-Eating Birds

Abstract

Analysis of Audubon Society Christmas-count data (1962-1971) revealed a generally synchronous pattern of winter eruptions between eight species of seed-eating birds whose winter ranges normally include boreal forests. Species and populations occupying montane conifer forests in the West did not fit this pattern as well. Literature analysis revealed a circumboreally synchronized pattern of seed crop fluctuations in certain high-latitude tree species and an apparently resulting pattern of southward eruptions of birds dependent upon these foods. Between 1948 and 1971 eruptions were relatively large in 1949, 1955, 1957, 1959, 1961, 1963, 1965, 1968, 1969, and 1971.