Ravens and Crows look very similar but Ravens are much larger. These two species, Common Ravens and American Crows, overlap widely throughout North America, and they look quite similar. Ravens often travel in pairs, while crows are seen in larger groups. Also, watch the bird’s tail as it flies overhead. The crow’s tail feathers are basically the same length, so when the bird spreads its tail, it opens like a fan. Ravens, however, have longer middle feathers in their tails, so their tail appears wedge-shaped when open.
Listen closely to the birds’ calls. Crows give a cawing sound. But ravens produce a lower croaking sound.
http://www.audubon.org/news/how-tell-raven-crow
The second photo below is a Raven, the rest are Crows.
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