PARIS—You can hear them in the trees around the Eiffel Tower, tweeting and trilling, straining to be heard over the constant revving of cars and trucks, the squawk of police sirens and walkie talkies, and the endless parade of tourists.

We don’t quite know if they are stressed, angry birds. The science only shows that they are loud-talking great tits —an urban bird also known as Parus major, with a black head, white cheeks and yellow body — that has adapted to be heard over big city noise.