While they are driving, I keep the pairs confined, except for their brief exercise period for food and water. When they are mated, I let out two pairs at a time, then three pairs and even four pairs at a time, taking care not to let out at the same time birds of new matings that were paired together in previous years. Once they are on eggs, you can open up the nest front permanently.
Taken from Widowhood Flying
By Mark Gordon