I agree that daytime kills throw suspicion on a mink or other weasel.
I also find a rattlesnake to be an unlikely culprit. Normally I'd expect a rattlesnake to leave town fairly soon if it were dealing with chickens it perceived to be a threat, which would make 1 kill possible, but multiple less likely.
However, they may be coming out of hibernation now, so there could be multiple snakes in the same area.
And second, I'm not sure, but I don't *think* rattlesnakes would consistently target the head/neck area. OK, I can see that repeatedly happening if the chickens are all walking up and pecking at it. Otherwise I'd expect to see bites to body on some, neck on others. Of course, it's possible the other chickens are being struck on the body, but the damage is being blocked by the feathers.
Maybe I've convinced myself it could be rattlesnakes after all.
Regardless, I'm intrigued, and want to know the answer!