Is he egg good

Question
I put in a nest bow about 2 weeks ago and my female parakeet already has one egg and is sitting on it will it be fertile how can i check

Answer
Its a bit odd that she's incubating if she only has one.  How long ago did she lay this one?  Budgies, if its a normal healthy clutch, will lay an egg every other day for around a week.  If she's been sitting on the single egg for a while, I wouldn't hold my breath.  You can check it with a flashlight when the female leaves the nest if its been more than a week.  If its been more than 3 weeks, its almost always a dud.