I was just wondering that say if you have an egg from a birds nest [For example Sara owl egg] is it possible to get another egg from a birds nest before hatching?

Yes.Use mtk, 5 workers on maples if you want eggs(atleast that's what I did quite a while ago when I was hunting for the eggs).

if your desperate just put max you can on maple rest on teaks and mahoganies. Otherwise do what Aslan said.

Yup, I've had a whole stack of eggs in my BA before, mostly from Miscellania.

what the heck do you do with eggs? I have like 200 of them, and I dont do pets, so if that is the answer I dont think I care. What the heck does a pet do?

You can use the Spirit Cobra to turn them all into Cockatrice egg variants, which sell for a nice amount on the GE.

 

Also, the pets serve as god items in the GWD. For example, if you have a Zammy Hawk out, it counts as a Zamorak item and zammy monsters won't attack you.