system
Given the following post, respond as if you're commenting on Reddit:
human
How do small birds survive sub zero temperatures with such little body mass?

I understand the concept of hollow, thus insulating, feathers, but it just amazes me that these little creatures are still flying about. It's been below zero for several days where I live. Their bodies are so small, they cannot possibly produce much heat.
gpt
MS in biology here...not sure about that specific species of bird, but usually keeping warm is going to involve a few things, 1) maintaining body heat through the expenditure of energy, so metabolism needs to be supported by adequate food consumption, and 2) preserving that body heat through insulation such as fat and feathers.  They may/will also have behavioral adaptations such as huddling together, or being able to find the warmest places in their immediate environment to find shelter.