Wow. We have had red-shouldered hawks nesting in the back woods for several years and they call all the time. Just now I had what I thought was was one right outside my home office window on the platform feeder: it was a blue jay, doing a perfect red-shouldered call. He called and called (cats were a bit startled) and then flew into the woods and did a few more times. My son came down getting ready for work and said "Hey, just heard a red-shouldered outside the window."
