Two lessons running at once
Cockatiels are natural whistlers, and males in particular pick up short tunes readily. The complication is that the same bird also owns a loud contact call designed to carry across open Australian country, and in a home he uses it to locate his flock — you. If screaming reliably brings a person into the room, even a scolding person, he has learned that screaming is his doorbell. Teaching a tune therefore works only alongside a household agreement about which sounds get answered. Whistles and soft flock calls earn company and praise. Screaming earns a patient wait until there is a pause, and then attention arrives during the quiet, so the quiet is what he repeats.
Expect the screaming to get briefly louder when you first stop answering it. That surge means he has noticed the old rule changed, and giving in during the surge teaches him to scream longer next time.
Choose and present a learnable tune
Pick a phrase of four to six notes with a clear rhythm, something every person in the home can whistle identically. Very long melodies blur for a cockatiel; a short, catchy fragment is learned in days and can be extended later. Whistle it when he is already settled and attentive — on his stand after breakfast, for example — in bursts of a minute or two, several times a day. Keep your face near his level, stay cheerful, and stop while he is interested rather than drilling until he turns away.
Reward approximations. A cockatiel learning a tune produces garbled versions first, mixing your notes with his own chirps. Respond warmly to those attempts, whistle the correct phrase again, and let repetition do the work. Many birds practise quietly to themselves when they think nobody is listening, so hearing muffled rehearsal from another room is a promising sign, not a cue to rush in and interrupt.
Protect the lesson from accidental rewards
Audit the household's reflexes. Uncovering the cage, refilling a treat dish, shouting back from the kitchen, or sending a child to check on him all pay the scream. Instead, when he screams, note the time, wait for several seconds of quiet, then go to him and whistle the tune. If he answers with any whistle-like sound, that is the moment for attention, a head scratch, or a small treat. Flat, boring waits for screaming and warm, interesting responses to whistling draw the line he needs.
Also meet the needs screaming often reports. A cockatiel left alone, bored, or short on sleep calls more. Build foraging toys, out-of-cage time, and regular flock time with the family into his day, and keep his nights long and dark, so the tune has less competition from a lonely bird's alarm.
Growing the repertoire calmly
Once the first phrase is reliable, you can add a second short phrase in separate sessions, keeping each tune's practice distinct at first. Whistle with him in call-and-response games, leaving gaps for his turn, which many cockatiels find more engaging than solo performance. Record progress loosely — which phrase he offers unprompted, and when — because birds often perform best at particular times of day, and scheduling sessions then speeds learning.
Contact an avian veterinarian if screaming is new and sudden in an older bird, or arrives with appetite loss, feather plucking, or breathing changes, since discomfort can drive vocal change. A qualified behaviour consultant can help if screaming dominates the day despite consistent rules. For the human side of the plan, KinsLe Care Teams keeps the response rule and short daily whistle sessions as shared household tasks, each marked done with a timestamp, so your cockatiel hears one clear message from his whole flock.