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Blue Jays are omnivorous, but most of the diet is plant material (up to 75% overall, more in winter). The diet includes acorns, beechnuts, seeds, berries, and similar foods. Blue Jays also eat many insects, as well as spiders, snails, birds' eggs and young, small rodents, frogs, and so on. Harvested acorns may be stashed in holes in the ground.
Courtship may involve aerial chases and the male may feed the female. Around their nest, Blue Jays become quiet and inconspicuous, but if the nest is threatened they will defend it loudly and aggressively. Blue Jays nest in trees, usually 2 to 9 m above the ground, but sometimes higher or lower. The nest (built by both sexes) is a bulky open cup of twigs, grass, weeds, bark strips and moss, sometimes held together with mud. The nest is lined with rootlets and other fine materials, often decorated with paper, rags, string, or other debris. The 4 to 5 eggs (sometimes 3, 6, or 7) are greenish or buff, sometimes pale blue, and spotted with brown and gray. Incubation is by both parents (but more by the female) for around 16 to 18 days. Young are fed by both parents and leave the nest 17 to 21 days after hatching.
Northern populations are partly (and variably) migratory, moving by day. Flights to more southern parts of the range in the fall may involve thousands of birds.
The Blue Jay's close relative in western North and Middle America, the Steller's Jay (Cyanocitta stelleri), is more commonly associated with coniferous forest.
(Kaufman 1996; AOU 1998; Dunn and Alderfer 2011)