A sunny day may send a male into an hour of song just because life is so wonderful. One behavior that may be mistaken for or develop into screaming is the instinct birds have to call to any flock members who are out of sight. Personally I chirp back, just to let them know where I am and that no predators have gotten me. This problem is lessened if you are definitely established as dominant since then the bird isn't responsible for your well being. Its aggravated if your single pet thinks of you as a mate.
Birds often get quite frantic when they are separated from their mates.
If the screaming is due to your inadvertently training the bird to scream you've got a very good chance of ending up with 2 screamers if you buy a companion. If you actively want another bird but have a screamer and are worrying about the new bird catching the bad habit you will probably want to get the screaming under control first, then get the second bird. Background copyright 1998 by Amy Patria. Do not copy without my written consent.