If you have another bird in the cage, whether male or female, you should remove the other from the cage permanently, unless you are breeding them. In which case you would removed any other males from the cage.
Usually this would not cause a problem. However, like people, birds are individuals, and it always possible that jealousy from a non-mating bird could interfere with the breeding bird's cycle.
You can buy them from pet shops. -------------------------------------------------- Look for local breeders in your newspaper as they are most likely in better health, hand fed and weaned.
A Cockatiel is a small, Australian bird. These birds can fly and each one is different from the next, (in color). These birds can also be kept as pets. Cockatiels are in the Parrot Family. They can...
You cannot. A female cockatiel needs a male cockatiel to mate with her before she will produce fertile eggs. And incidentally, birds do not "fall pregnant".