You say you can call them in OK, so its not your calling.

My guess is that they are seeing something they don't like. Be aware that they have an uncanny sense of placement of where sound is comming from. They may see the decoy, but that's NOT where the calling is comming from. Don't call when they're in sight if you can help it -- especialy if they're comming in already. Pick your setups carefully with lots of cover and SIT VERY, VERY STILL. I've had them bust me from a blink! Be very aware of your movements -- ANY movement -- even to the point of controlling your breathing. Make sure that your watch is covered and that your glasses (if you wear them) don't glint, your belt buckle doesn't shine, and don't wear white socks. THEY SEE EVERYTHING.

Think pure thoughts -- they see those too.