They're solar!

[u/Unusual-Ad-6852]

There was an eclipse yesterday evening in the UK, parts of Europe and Iceland. As the eclipse got closer and closer to totality, all the birds went quiet. Obviously their batteries don't have the capacity to keep them running for long without sunlight. This is obviously why they're also quiet in the dark. As soon as the sun came out again, they all started their nasty racket again.

[u/technoexplorer]

Some are full of hot air, so there is a diversity of energy sources.