I use a treadle feeder too. It has been outside for years and is not much worse for wear.
It used to have a label on it that said "Chookateeria". It doesn't have adjustable openings like Ribh's, I just use a clothes peg to prop it open and make the opening smaller and smaller by moving the peg forward until the chooks get the idea.
I have a treadle feeder too, two in fact (but the newer one isn’t being used). When I had three ISA Browns they learned to use it beautifully, but then Charlie the Australorp and Bessie the Barred Rock were so big they could reach it without standing on the treadle, and couldn’t work out how to get into it. The Faverolles can use it but will often stare helplessly at it until I put a brick on the treadle.
