It is near the end of breeding season, and the crows just raised a bunch of young ones. They are ready to leave the nest and follow the parents around. They are almost as big as their parents are but they still beg for food. Young crows stay with their family for the first year, to help raise the young of the next season. So, you often see crows travel in large family groups year round. Ravens, which are larger than crows, do not stay with their parents. Instead young ravens form huge flocks and then they pair up and leave the flock. Ravens form pair bonds for life and they travel in pairs year round, and their young will not stay around to help them. If you see a flock a a hundred or more, then they are ravens, not crows. The calls of the raven are lower pitched than those of the crows. A typical flock of crows will only number a few to a dozen or so, not in the hundreds.
Following image is a flock of young ravens that have not found their partners for life yet. They try to impress other ravens with their ability to find food. That ability, instead of beauty, is what is attractive to other ravens.
In contrast, the following image is what a family of crows may look like as they go searching for food.