Thanks Merv, but I need a new set of teeth before I can try your idea - tempting though it may be.
Thanks EmmaJane - good idea. Which means I no longer have any spare - sorry.
Since posting my original question, I cut another head down, and placed it on a bucket, leaning upright on the wire mesh fence, so that Mrs Turkey could help herself. It was hilarious to watch her (from a short distance) extending her neck to full length, and tilting her head back and forth to examine this strange thing. I don't think she had any seed, but after I removed the head on leaving for home, noticed that some seed had been removed at the bottom, and reckon it was one of the chickens in the same pen.
I have a rapport with Mrs T; if I find a caterpillar, I will call her over to the fence, hold my hand out with the caterpillar on it for her exclusive feed.
It's the same with the ducks, on the opposite fence. When they first went into their pen, they would run to the opposite side of the pen if I approached the fence. Then, as I found slugs and snails to throw at them, they started to run towards me when I approached the fence - quacking in chorus of course.
Never a dull moment when you've got chickens and turkeys one side, and ducks t'other. Incidentally, if Annie goes into the chicken pen, she ignores the chickens, and they ignore her, but we have to watch Mr T. because he tries to bonk anything - including Annie.