Although you can read widely on Whitman and his work, about his personality and beliefs, I'm writing here to focus on his interest in a bird - the Hermit Thrush.
In his famous elegy for Abraham Lincoln, written shortly after Lincoln's death, he incorporated lyric imagery about the Hermit Thrush in the 206 lines of "When Lilacs Last in the Door-yard Bloom'd".
More on the poem, the repeated emphases on the thrush and its song, and perhaps why Whitman chose this image: https://hokku.wordpress.com/2015/04/26/whitmans-trinity-of-remembrance-when-lilacs-last-in-the-door-yard-bloomd/
Some say the Hermit Thrush is North America's finest avian singer. As subjective as that evaluation may be, most of us who have heard it will at the very least agree it is a wonderful song.
Hear one at: https://www.allaboutbirds.org/guide/Hermit_Thrush/sounds
Read more at: https://northernwoodlands.org/outside_story/article/twilight-singer-hermit-thrush
And about Hermit Thrushes' song variation: https://academic.oup.com/auk/article/134/3/612/5149313
But finally, let Whitman have his say; let it drift over you, like the thrush's song itself:
4
5 In the swamp, in secluded recesses,
A shy and hidden bird is warbling a song.
6 Solitary, the thrush,
The hermit, withdrawn to himself, avoiding the settlements,
Sings by himself a song.
7 Song of the bleeding throat!
Death's outlet song of life—(for well, dear brother, I know,
If thou wast not gifted to sing, thou would'st surely die.)
and again a bit later...
13
20 Sing on! sing on, you gray-brown bird!
Sing from the swamps, the recesses—pour your chant from
the bushes;
the bushes;
Limitless out of the dusk, out of the cedars and pines.
21 Sing on, dearest brother—warble your reedy song;
Loud human song, with voice of uttermost woe.
22 O liquid, and free, and tender!
O wild and loose to my soul! O wondrous singer!
You only I hear……yet the star holds me, (but will soon
depart;)
depart;)
Yet the lilac, with mastering odor, holds me.
