A murder of crows

Yesterday when I got home from work and let the dogs out in the back yard I looked up and saw crows flying from west to east.  Lots of crows.  For over 20 minutes.  There were hundreds of them that I could see, maybe a couple of thousand over the entire period.  I took a video of some of it - Crows over Baltimore.  To be honest, it was kinda creepy.  Yet at the same time I thought what a great mood setter for a game.  How would players react to seeing a couple of thousand crows flying in one direction overhead?  It isn't really anything they can directly interact with, but they're left with a choice - go where the crows are going, go where they came from, or ignore it.