I don't know a great deal about bird song myself, but I gather the subject has lots of interesting subtleties, especially when applied to live audio or real-world recordings where it isn't necessarily known where the bird soounds appear or how many birds there are.
A weekend, or a PhD!
The Machine Listening group at QMUL covers bird audio - see Dan Stowell's work for example: http://c4dm.eecs.qmul.ac.uk/people/dans.html
Here's a Bird Audio Detection Challenge from 2018: https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111... http://dcase.community/challenge2018/task-bird-audio-detecti...
I don't know a great deal about bird song myself, but I gather the subject has lots of interesting subtleties, especially when applied to live audio or real-world recordings where it isn't necessarily known where the bird soounds appear or how many birds there are.