You are the Royal Food taster.I feel your pain. My girls are total snobs, too. All food that hasn't been eaten regularly is surely poison and they will literally turn their backs on it. They are so picky that tiny bright red grape tomatoes are their favorite. They turn their bills up at other tomatoes, even though they almost bite my hand off eating tomatoes. Brats.
My ducks also rejected dubia roaches. And they don't like black soldier fly larvae. Mealworms only. Thank you.
So, one way I've convinced my ducks that new food is not poison is the way you mentioned. Slip a tiny bit of new food in the food they like. My ducks eat around the new food disdainfully for about 3-6 weeks before starting to eat it and then I increase the new food slowly.
The other way might only work with my ducks. My ducks are obsessed with eating food that I'm eating. So if I want them to try something I get a bowl of it myself, sit on the ground, and start eating it. I ignore them as they come closer, maybe pretend to read a book. They'll make a mad dash at my bowl eventually and get a bite or two. I scoop up my bowl and pretend to be outraged while they beg for more. I give in and hand feed it to them.Ducks.
It didn't kill you so now the kings and queens can eat it.
