The origin of this phrase isn’t what I would have thought. Eggs are a beginning for birds, but the phrase comes from a different beginning involving eggs.
ab ovo, phr.
From the (very) beginning.
Cf. Hor. Sat. i. 3. 6 ab ouo usque ad mala ‘from the egg to the apples’, alluding to the Roman custom of beginning a meal with eggs and ending it with apples; and Hor. A.P. 147 Nec gemino bellum Troianum orditur ab ouo, in allusion to the twin egg from which Helen of Troy was born.