Early bird feeds the worms.

[dared]

Early bird feeds the worms.
 
The first chick to hatch
Was christened by the children
Lulu, first of her name.
Nicely playful to announce his name. But it did get me confused if it's he or she because I think he is being referenced as a cockerel? Just a bit confusing but that may be your intent with the playful tone.

Though three promptly followed
No more names were issued
Until destiny swooped
To earmark; coop or stove.

Honestly, a bit confused here again, I'm guessing they just got named to earmark/coop/stove? Or is it what happens to them?
 
Full plumage erupted Love the imagery so I guess this is when lulu becomes a man.
Necks stretched to wringing length Ready to be beheaded huh?
And resplendent crests showed
Us, the cocks from the hens.
 
So Lulu made the plate
His girls were sent to lay
The key to long and sheltered life?
Be a cockerel, nay. Nice ending, though could possibly play up the bitter ending of it, just to contrast with the humour to make it pack a bit of punch. Not to make people cry or anything, but just to hit a bit harder.

Overall a good read. A bit ambiguous or archaic in language but it worked in this poem due to the humorous nature of it. I think maybe a bit of clarity would be good though, just a bit more in-depth to make it more accessible.