As reported by [wired]:

As tragic as the global pandemic has been, its also had a few silver linings as it puts humanity on hold. Notably, a dramatic reduction in noise pollution in urban environments. As a result of this, Songbirds such as the white-crowned sparrow have shifted and adapted their melodic songs when communicating with each other into lower band frequencies, now that they're not being drowned out. How they can shift and modulate their calls and the range of frequencies, adaptation, and mixture of how they communicate and interact with each other offers a rare glimpse of their intricate culture outside the world of man, and how much of an impact we have on them.