It's known that birds migrate at night - it's been quoted they use the stars or the earths magnetic field. Clear nights rather than cloudy nights.
Two further separate bits of information (perhaps) had me wondering ...
1) Birds can see in the UV part of the spectrum
2) The night sky looks very different in the UV spectrum (source - trailer for the forthcoming Stephen Hawking film.) Paraphrased "It glows like nothing else you've seen", or something like that.
If no. 2 is correct, anyone heard anything along these lines before? Can't say I have tbh.
It is also noted that cloud usually inhibits uv light from reaching the earths surface (UVB).
What would the night sky look like to a bird in the UV end of the spectrum?
Thoughts/any reference to this elsewhere? (My quick google search didn't come up with anything).