Would this also be the way you would say "The birds sang about the spring"?
Is there a simple way to say either one more clearly, so there is no confusion?
Perhaps sang i løpet av våren for sang in/during spring. I don't think there's a clearer way to say "about spring."
Would one translate "in spring" (without the article) as "om vår"?
Nope, still "om våren".