AS: ...the last, fifth, stanza of The Lord Forbid my Going Mad (1833)...Pushkin mentions a nightingale:
And I shall hear at night neither the brilliant
voice of the nightingale,
nor the dense forest's murmur,
but my companions' cries,
the oaths of the night wardens,
shrill sounds, the clink of chains.
In the Commentary to his Translation of Pushkin's Eugene Onegin (note to Seven:VI:5-6; vol. 3, p. 74 of the Princeton/Bollingen edition), Nabokov (the above translation from Pushkin is his) says that the epithet "brilliant" (yarkiy) is Pushkin's special code in which he signals his awareness of Batyushkov's madness. The same epithet, unusual in the Russian poetry for the nightingale, was used by Batyushkov in his elegy The Last Spring (1815): "The brilliant voice of Philomela / has charmed the gloomy pinewood".

...Let's now switch from Pushkin to Tyutchev, author of the short poem Bezumie ("Madness", 1830). In his eight-line poem Vecher mglistyi i nenastnyi ("A misty, foul-weathered evening", written in the 1830s) Tyutchev speaks of the shock he expierenced when hearing the skylark, a bird that sings (unlike most other birds, while soaring above the ground) before noon, at an unusually late hour. The bird's voice stunned the poet's soul like a horrible laughter of madness: Kak bezum'ya smekh uzhasnyi / On vsyu dushu mne potryas.
Let's now switch from Russia to England ("where poets flew the highest", according to Shade; see Kinbote's note to l. 922). To a Skylark ("Hail to thee, blithe Spirit, / Bird thou never wert...") is the famous poem (1820) by P. B. Shelley. Its last stanza reads:
Teach me half the gladness
That thy brain must know,
Such harmonious madness
From my lips would flow
The world should listen then - as I am listening now. 
"Shelley's incandescent soul" is mentioned in Shade's poem The Nature of Electricity (see Kinbote's note to l. 347). On the other hand, the title of one of Shades' books of poetry, Hebe's Cup, seems to refer to the last stanza of Tyutchev's poem Vesennyaya groza ("The Spring Thunderstorm", 1828) that mentions yet a third bird, the eagle:
You'd say: the frivolous Hebe,
feeding Zeus' eagle,
has spilled on Earth, laughing,
the thunder-boiling cup.
Add to this that Shade's parents were ornithologists, that his wife's maiden name is Irondell (which comes, according to Kinbote, from hirondelle, French for "swallow") and that his last unfinished long poem begins with an avian image ("I was the shadow of the waxwing").

(A.Sklyarenko)

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Skitalets is the penname of Stepan* Petrov (1869-1941), a writer and a friend of Chekhov. Comparing Skitalets (who was a professional pevchiy, chorister) to more popular Leonid Andreev, Chekhov (who himself was a choirboy as a child) used to call the former "a live sparrow" and the latter "an artificial nightingale." Skitalets is Russian for "wanderer." Nabokov is the author of Skital'tsy ("The Wanderers," 1923, by Vivian Calmbrood), a play in verse. (A.Sklyarenko)

Jansy Mello: Coincidences are fun to report. While I returned to the writings of W.R.Bion, who once quoted Bishop of Berkeley's "ghosts of departed increments," the first item that reached my eyes related to... skylarks!  Only the "coincidence" relates to Nabokov, not its content. 

W.RBion (1976) described a cartoon from Punch Magazine in which "a small boy draws an adult's attention to a lark singing in the sky. He states, "Hi, mister, there's a sparrer up there an' 'e can't get up an' 'we cant't get down an' 'e ain't 'arf 'ollering'."

The lark story was associated to easy and complex questions and patterns: "During the Second World War I encountered the Matrix Test, imposed on member of the British army. Men were expected to choose one pattern out of several to omplete a page of incomplete patterns....One man was certain that the tests could not be so ludicrously simple, and proceeded to measure the patterns offered and the vacant spaces. Consequently, his score was zero...Why can't he believe that a simple answer is the correct one?" (aso*)