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: http://biology.allaboutbirds.org/bird-song-hero/
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.