The Irruptive Seedeaters And Fruiteaters

Species known for their irruptive migrations are listed in Table 18.1, along with their main food plants. Most species eat mainly different foods in summer and winter and, like most birds, migrate twice each year, away from the breeding range in autumn and back in spring. Some such species eat mainly seeds year-round, but different types of seeds at different seasons (e.g. Common Redpoll Carduelis flam-mea, Eurasian Siskin C. spinus). Others eat mainly insects in summer and seeds (or fleshy fruits) in winter (e.g. Bohemian Waxwing Bombycilla garrulus, Brambling Fringilla montifringilla, Evening Grosbeak Hesperiphona vespertina). The latter tend to concentrate in summer in areas with insect outbreaks (e.g. the Brambling in areas with high densities of the moth Epirrita autumnata, and the Evening Grosbeak and others in areas with Spruce Budworm Choristoneura fumiferana, Morris et al. 1958, Enemar et al. 1984, Lindström et al. 2005). In contrast to all other species, however, crossbills and nutcrackers eat conifer seeds year-round. They apparently make only one major movement each year, from regions where last year's crops were good to regions where the current year's crops are good (see later).

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