The vivid cobalt or azure of a blue jay (Cyanocitta cristata) feather is instantly eye-catching but in fact there is no blue pigmentation in birds' feathers and the colour is a result of light refracting in the feather's particular inner structure. Squash the feather and the colour goes.

The call of the blue jay has been described as an 'unrelenting steel-cold scream', rather unkind but very near the mark. This perky, popular bird, often caricatured in books and cartoons, is the sentinel of the woods and forests, calling out its raucous jay-jay warning when it spots an intruder. Its elegant appearance is exposed as a sham at the bird feeder where it pushes and shoves others out of the way. An omnivore, it performs a great service by devouring the pupae of the pestiferous tent caterpillar, each pair feeding hundreds to their nestlings in the early summer.

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