Why are crows cawing at me? Meaning? Sign?

Every morning, when I go out to walk, at a certain point, there is always a huge flock of crows that fly over me. Continuously, I see more and more, they all start to caw, but then at the end of my walk, I see a single one. This one is always alone and sitting at the highest point on a tree and cawing loudly down at me. It's bizarre and has been happening consistently for more than a week now, I am a very spiritual person and believe it means something. Does anyone have a theory to what it might be?