Any small passerine of the Fringillidae family, but probably the Chaffinch Fringilla coelebs, Pinson des arbres.
2 occurrences (1 finch, 1 finch-egg)
MND 3 1 125 The finch, the sparrow, and the lark,
TRO 5 1 35 p Finch egg!
The Chaffinch must have been the most common bird in Britain and was recorded for the first time by Aldhelm of Malmesbury in about 685 AD.
It is therefore logical that Bottom should place it along other very common birds in his song:
The ousel cock so black of hue,
With orange-tawny bill,
The throstle with his note so true,
The wren with little quill.
The finch, the sparrow, and the lark,
The plainsong cuckoo grey,
Whose note full many a man doth mark,
And dares not answer 'Nay' -
(MND 3 1 120-3 [...] 125-8)
HARTING adds that it "has always been a favourite cage-bird with the lower classes".
"Egg" seems to have been a common expression used to designate something worthless, especially the egg of such a small species, even if it is not the smallest one. In Coriolanus (4 4 21) we can find: "Some trick not worth an egg" and the murderers in Macbeth called Lady Macduff's son "you egg!" before stabbing him. And then, when Thersites and Patroclus are abusing each-other, Thersites after having said to Patroclus: "ah, how the poor world is pestered with such water-flies!, diminutives of nature!"(TRO 5 1 32-33) adds in the same vein: "Finch-egg!"(35).