Do nightingales sing all year?

Answer 1

Though I don't like using it, Wiki is the easiest source on this. They don't mention anything about there being only a specific season for the song, only a time.
http://en.wikipedia.org/wiki/Nightingale

Ah, further research brought this up:
""Singer of the night" is the literal translation of its scientific name, although during some weeks after its return from its winter quarters in the interior of Africa it exercises its remarkable vocal powers at all hours of the day and night. "

So, depending on where you are, I guess it would be considered a seasonal song. Can't sing if it isn't there.
http://www.crockerfarm.org/ac/gr3/minstrel/nightingale.html