Sometimes we have a hard time telling whether we are looking at a grackle or a crow. This is how we decide:
- A crow is a little larger than a grackle. But unless the two birds are close to each other, relative size may be difficult to determine.
- A crow is only slightly glossy but a grackle is iridescent.
- A Grackle’s tail will be longer, but again there’s the relative size thing.
- A grackle’s eye is white and the eye of a crow is dark.
An adult grackle has 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. An adult female, beyond being smaller, is usually less iridescent. 
The Common Grackle forages on the ground, in shallow water or in shrubs. It will steal food from other birds. It is omnivorous, eating insects, minnows, frogs, eggs, berries, seeds, grain and even small birds and mice. Grackles at outdoor eating areas often wait eagerly until someone drops some food. They will rush forward and try to grab it, often snatching food out of the beak of another bird. Grackles prefer to eat from the ground at bird feeders, making scattered seed an excellent choice of food for them. 
Grackles practice something called ‘anting’.  Anting is a behavior during which birds rub insects, usually ants, on their feathers and skin. The bird may pick up the insects in their bill and rub them on the body, or the bird may lie in an area of high density of the insects and perform dust bathing-like movements. The insects secrete liquids containing chemicals such as formic acid, which can act as an insecticide, fungicide, or bactericide. 
Unlike many birds, the grackle benefits from the expansion of human populations due to its resourceful and opportunistic nature. In some areas, it is now considered a pest by farmers because of their large numbers and fondness for grain.
Grackles are loud,noisy and gregarious. They are also are pushy birds and will nudge other birds out of the way at feeders. 
Grackles are here in Peachtree Park year round.
References and Additional Information
 Wikipedia: Common Grackle
 The Sibley Guide to Birds, second edition – David Allen Sibley
 Cornell – All About Birds: Common Grackle
 Cornell – All About Birds: Common Grackle – sound
 The Breeding Bird Atlas of Georgia – UGA Press: Schneider, Beaton, Keyes and Klaus, Eds.
 Cornell – All About Birds: Common Grackle – life history
 Wikipedia: Anting