This is a short entertaining video with several spectrograms of the birdsongs from some well-known songbirds.  It was created by the Cornell  Lab of Ornithology.  They recommend the following link for further info:


This is a video of a lecture by Donald Kroodsma on The Singing Life of Birds.  It describes some of the highlights from his book of the same title.  The lecture begins at time 4:40.  There are some great spectrogram examples at about time 10:00.

The Singing Life of Birds from Cary Institute on Vimeo.