Why do sparrows and other small birds ruffle their feathers in winter.

Birds ruffle their feathers because of the cold. This has a physical explanation. Air is a poor conductor of heat. Therefore, people put two-chamber windows that retain heat. Homes are insulated with foam and so on. Also, when it snows, the plants can survive, as the heat is stored thanks to the air gap. Birds are also warming up. Rather, it does not warm, but does not allow you to quickly lose body heat. Accordingly, birds can survive in the most severe frosts thanks to this adaptation.