Synchrony and Periodicity of Eruptions by Boreal Birds

Abstract

Abstract I examined 38 years of Christmas Bird Count data in order to resolve conflicting earlier findings as to whether eruptions of boreal seed-eating birds are synchronized and occur at regular intervals. A total of 15 species was analyzed, including several largely insectivorous boreal species. Interspecific synchrony was common, with 34 species pairs (32% of a possible 105) statistically synchronous across all or part of North America and clusters of up to five species exhibiting significant synchrony in all pairwise combinations. Within-species synchrony was significant between eastern and western North America for five species. The relationship between interspecific synchrony and diet was weak and significantly higher among species in the same diet category in western North America only. Periodicity as measured by temporal autocorrelations in mean winter density at lags of up to three years was significant for eight of the species in at least one of the geographic regions; four of these (Red-breast...