Male or female?

Question
We have three birds in a cage and believe that one may be a boy as eggs
continue to appear. However, the real question is two parts. First part: How long
is the gestation period? Second part: If you catch one of the birds, is there a way
to visualy see the diff?  

Answer
Do you mean how long it takes the eggs to hatch or what?
If you catch them and blow on the rear to see if there are feathers or not is a good way to tell. I can't remember which has no feathers around there but I think it's the females that have no feathers around the rear but I can't be sure.