A robin has built a nest in a small fir tree just out front of my house. About a week ago their were 4 eggs and the robin was actively sitting on them. Had a peak today and there are only 2 eggs not hatched yet and the robin is still sitting on them. Would the robin have removed the other 2, 4 eggs seems like a lot for a robing pair to raise. Just curious if birds do this on their own.