21.   I never tire of bird song and sky and weather.

22.   I was locked outside, listening to bird song and looking at trampled thistle.

23.   If the river disappears, bird songs will be silenced in three countries.

24.   It is a landscape of silent stone and quiet grass and bird song, and its utter peacefulness holds no sign of the violent deeds of those interred within.

25.   Its Third Avenue windows are filled with figures wearing feathered hair ornaments against a striking background of black crows and blackened tree branches and the tweet of bird song.

26.   Moldenhauer and his students seek to discover whether bird song is learned or innate.

27.   On one recent afternoon, the quiet is punctuated with bird song.

28.   Now, bird song fills the site.

29.   On this afternoon near Thacher State Park, Oliver sets up a tripod in a meadow flush with monarchs and bird song.

30.   Other sources, besides bird song and purely abstract formulations, included opera, Asian music heard on record, and the poetic meters and forms of Greek drama.