Either you want to figure out what it is or you don't.  Looking at footage of the cameras throughout the day is the best way to do that.  Or sitting on your porch all day watching them.  If you don't want to do it every day, clean up all the feathers and the next time you notice a pile, review the footage from that day.  It should be fairly obvious by scanning the photos, you don't have to look at each one in detail, like some form of Chicken Criminal Minds.  Normal chicken behavior is just that, normal.  It won't stand out.  When you see blurs and flapping look at those closer.  Or literally, just scroll until you see a dog.  You know your neighbors have them, so you know what they look like.  I don't know of anyone with the power to divine what the issue is, so some effort is going to have to be put in on your part to determine why the feathers are appearing.  Unless of course, you know a Navajo. 
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