I pass this bush on the bike path regularly, and recently it was full of song. Hundreds and thousands of tweets and whistles...but all invisible. It was almost as if the dried branches were singing to welcome the warmer weather.
Of course, it was birds--but so well camouflaged that, even with close inspection, they were nearly impossible to see. In fact, I was only really able to locate one:
and I am sure there were many more. Regardless, it was a nice serenade for spring!