Crows are real smart. On an episode of Roderick on the Line, John Roderick recalled a story he read where a researcher was trying to round up crows for tests. He went into a parking lot and tossed a net, capturing some. The next day, he went to a different parking lot across town and the crows immediately flew away when he pulled in, because they recognized him. He went back to the same second parking lot in a different vehicle and was able to capture some, but then that vehicle didn't work. He started wearing masks and trying all sorts of tricks, but as far as he could tell, the crows were communicating through town.
Regularly, I'd walk in a park near my workplace to work out problems and I began too often to play games and tricks with the magpies (another type of Corvid like the crow). I'd do things like throwing twigs on either side of them to see how they would react (no magpies ever injured!). After a while I'm certain the magpies had a particular warning call any one would call out when I arrived in the park that would set them all of making that cawking sound until I left. After a while I needed to avoid the park for a bit and I think I was forgiven when I slowly started integrating myself in by leaving bits of food like nuts.
I was amazed too at how observant they were, keeping a different distance if they noticed I had am umbrella or something in my hand or if I was walking funny.
