Thanks for the update!! That's what I love about this, you just saved me a ton of time by sharing your experience!!Freeze Update on the cup waterers.
I've only had a couple nights that got into the 20's so far so this is an "early report". Keep in mind that I have a bird bath heater in the bucket so the water in the bucket is between 40 - 60 degrees at any given time. My concern for freezing has been the water inside the little necks leading into the cup.
The nights that it got that cold, on cup B (see photo below), the mechanism froze. It's the one with the little metal spring in there and I'm thinking that metal spring is what was freezing up. I pushed on it and tried to get the water flow open and was eventually able to but I know that the chicken beak wouldn't have been able to get it flowing. Now that was after only a few hours at 25 degrees so I imagine if it gets down and stays in the 20's that one won't work very well.
Cup A did not freeze.
I had the same results on both freezing nights. Of course, if there is any water pooled in the cups that will freeze also, but these are designed to only let water down when the beak toggles the "nipple" and there is usually very little water in the cup at any given time.
Today I removed cup B and replaced it with another "cup A". I'll update again after we've had a longer cold-spell.
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