#1 I worked with a specific family of crows along north Lake Shore Drive in Chicago. "My" crows recognized a few calls and would respond to me. However, in the spring and fall I would notice larger gatherings of crows up and down the lakeshore. When I would give out the calls my family recognized, inevitably one or two or more crows would respond, and usually come to see what I was doing. This behavior would lead others in the larger flock to also become curious and approach me.
This indication of detailed communications between different families was amazing to me.
#1 In the years I spent with a family of crows, I would regularly observe them hunting cooperatively for food. One or two crows might be perched along a street, and if they spotted a meal (french fries, road-squirrel etc) one crow would call out to notify the family. As the others gathered, the crows would take turns; one or two will stay in an elevated observer position, and let out warning noises if they saw oncoming traffic, pedestrians, prowling cats or the like.