I’ve written two articles about this work, one for UK teachers and one for US teachers.
Although the core idea is the same in both cases, they are different and if you have got this far then I suggest it’ll probably be worth reading them both. Click the bird for the UK PDF and the US bird will generate an email to ask nicely.
Using birdsong to support the teaching of sound and graphs
School Science Review (Volume 96, Issue 356) March 2015 (you might need to right click and save as..)
Physics and Birdsong: “Listening” with Graphs”
The Physics Teacher (Vol.57, Issue 6) September 2019