are crows a bad omen?

Yesterday when I was at work Jake (the 3-yr-old I nanny) and I were in the living room getting ready to go pick up his sister when all of the sudden this enormous flock of birds land in the trees out front. They were so loud, screaming and caw-ing, that they actually drown out the TV. It was really creepy. Then when Jake and I walked outside I noticed there were a bunch of people including stopped cars all standing around and watching the crows- who were going even more insane and flying low and just being all apocolypitcally foreshadowing. Then they started dropping from the sky, first just one or two and then a whole bunch. I counted 11 before Jake and I got in the car to go pick up his sister. When we got back I saw a bunch of neighbors and animal control people picking up the carcasses and I asked if anyone knew what was going on. One guy said he say a hawk up there trying to get the crows and another guy said from the way the crows were twitching on the ground after they fell he was sure they had to have eaten rat poison. So weird!