Here's the poem

1 Thou still unravish'd bride of quietness,
2 Thou foster-child of silence and slow time,
3 Sylvan historian, who canst thus express
4 A flowery tale more sweetly than our rhyme:
5 What leaf-fring'd legend haunts about thy shape
6 Of deities or mortals, or of both,
7 In Tempe or the dales of Arcady?
8 What men or gods are these? What maidens loth?
9 What mad pursuit? What struggle to escape?
10 What pipes and timbrels? What wild ecstasy?

11 Heard melodies are sweet, but those unheard
12 Are sweeter; therefore, ye soft pipes, play on;
13 Not to the sensual ear, but, more endear'd,
14 Pipe to the spirit ditties of no tone:
15 Fair youth, beneath the trees, thou canst not leave
16 Thy song, nor ever can those trees be bare;
17 Bold Lover, never, never canst thou kiss,
18 Though winning near the goal yet, do not grieve;
19 She cannot fade, though thou hast not thy bliss,
20 For ever wilt thou love, and she be fair!

21 Ah, happy, happy boughs! that cannot shed
22 Your leaves, nor ever bid the Spring adieu;
23 And, happy melodist, unwearied,
24 For ever piping songs for ever new;
25 More happy love! more happy, happy love!
26 For ever warm and still to be enjoy'd,
27 For ever panting, and for ever young;
28 All breathing human passion far above,
29 That leaves a heart high-sorrowful and cloy'd,
30 A burning forehead, and a parching tongue.

31 Who are these coming to the sacrifice?
32 To what green altar, O mysterious priest,
33 Lead'st thou that heifer lowing at the skies,
34 And all her silken flanks with garlands drest?
35 What little town by river or sea shore,
36 Or mountain-built with peaceful citadel,
37 Is emptied of this folk, this pious morn?
38 And, little town, thy streets for evermore
39 Will silent be; and not a soul to tell
40 Why thou art desolate, can e'er return.

41 O Attic shape! Fair attitude! with brede
42 Of marble men and maidens overwrought,
43 With forest branches and the trodden weed;
44 Thou, silent form, dost tease us out of thought
45 As doth eternity: Cold Pastoral!
46 When old age shall this generation waste,
47 Thou shalt remain, in midst of other woe
48 Than ours, a friend to man, to whom thou say'st,
49 "Beauty is truth, truth beauty,--that is all
50 Ye know on earth, and all ye need to know."

To me it also brought to mind Yeats' The Second Coming chock full of bird and time references.

Turning and turning in the widening gyre
The falcon cannot hear the falconer;
Things fall apart; the centre cannot hold;
Mere anarchy is loosed upon the world,
The blood-dimmed tide is loosed, and everywhere
The ceremony of innocence is drowned;
The best lack all conviction, while the worst
Are full of passionate intensity.
Surely some revelation is at hand;
Surely the Second Coming is at hand.
The Second Coming! Hardly are those words out
When a vast image out of Spritus Mundi
Troubles my sight: somewhere in the sands of the desert
A shape with lion body and the head of a man,
A gaze blank and pitiless as the sun,
Is moving its slow thighs, while all about it
Reel shadows of the indignant desert birds.
The darkness drops again; but now I know
That twenty centuries of stony sleep
were vexed to nightmare by a rocking cradle,
And what rough beast, its hour come round at last,
Slouches towards Bethlehem to be born?