@Pollo Blanco ..I... don’t see how this is helpful? The OP expressed concern because the temps were much lower than their ducks have been used to and was looking for a bit of reassurance from those who are in a similar situation... It is sometimes harder to tell with poultry than it is with dogs or cats, when they’re truly cold... but they generally seem to know what they can and can’t handle. Giving them the option to choose is usually sufficient.
I haven’t used supplemental heat for my ducks at all. They have their draft free but ventilated house, a pen with a windbreak, and deep bedding. No issues whatsoever, but if I had obvious signs of them being “too” cold, I’d provide them with something to adjust that, without going overboard.
and, just to bring in a bit more perspective from over here in the North... my shep/husky dog spend every moment outside if at all possible, by her choice. She wears her coat in the -40 or lower overnights on my insistence, but beyond that, she’s totally fine. It’s much worse for her coming into even the unheated porch, and then going back out, because the temp difference is just too radical. She’s never been a house dog... every situation is going to be different.