Adult Common Grackles measure from 28 to 34 cm (11 to 13 in) in length, span 36–46 cm (14–18 in) across the wings and weigh 74–142 g (2.6–5.0 oz). Common Grackles are less sexually dimorphic than larger grackle species but the differences between the sexes can still be noticeable. The male, which averages 122 g (4.3 oz), is larger than the female, at an average of 94 g (3.3 oz). Adults have a long, dark bill, pale yellowish eyes and a long tail; its feathers appear black with purple, green or blue iridescence on the head, and primarily bronze sheen in the body plumage. The adult female, beyond being smaller, is usually less iridescent; her tail in particular is shorter, and unlike the males, does not keel in flight and is brown with no purple or blue gloss. The juvenile is brown with dark brown eyes.

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