system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: How is it that some birds can exist in such wide temperature ranges with no apparent discomfort?

I live in an area where it regularly gets to be above 100 °F and today the temperature was as low as 31 °F. I saw, what I think is, a Great Blue Heron standing in a river. I assume it was waiting to catch a fish. How can they deal with such wild temperature extremes? I would assume that the water felt even colder than the air.
gpt
Feathers are extremely good at dealing with temperature regulation, a lot more so than fur which only insulates but doesn't cool an animal down. Feathers include multiple layers of insulation to keep the bird warm, but the feathers themselves can also flush blood through the shafts in the middle of them to cool a bird down.

This is part of why many birds can live in a larger variety of areas than similar mammals can.

As for standing in cold water, scales do give the legs some insulation but it wouldn't be very much, they just put up with being cold at that point.