They classified four distinct dialects of white-crowned sparrows in urban and rural communities and studied the changes of their bird song when background noise levels lowered during the pandemic. They measured a doubling of the signal-to-noise ratio of bird songs to urban noise, which doubled the distance you can hear birds and lead to a 4-fold increase in the amount of birds that you heard during that time.
I recently learned how to distinguish between different bird types by appearance and their songs thanks to Merlin Bird ID, which is essentially a Pokédex for birds. Being able to identify different bird species has been eye-opening since I had never paid much attention to the different songs and behaviors of different birds.
Anyone can record audio and the spectrum of bird songs in the recording can be used to classify the bird species. It's super accessible to anyone who's interested in getting started.
Also, white crown sparrows are really cute.
[1] http://www.engdes.com/sigwin/company/biblio/papers/Singing%2...