Could they be ravens?I don't know, but some of the crows I've seen here are almost as big as my cat.
(From the Audubon page)
Ravens are larger, the size of a red-tailed hawk. 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.
One other observation from my own experience as I had a pet raven, crows tend to hop where a raven struts around like he owns the place. (Very full of themselves)