My first had spread her darksome wing

My first had spread her darksome wing
O'er all the loveliness of spring ;
My third arose with mournful wail —
The young leaves told their first sad tale,
The old oak groaned, the flowerets sighed,
The hawthorn bloom was scattered wide :
But ere my gloomy first had passed,
When silent was my third at last,
My whole awoke the moonlight dell
To list the sweet tale she could tell ;
Then mingled, in strange harmony,
Silence and sweetest melody.
'Your second, why such strange omission ?'
'T is but a tiny preposition.