Yes, cockatiels can whistle, and they generally start learning around three months of age. However, the exact time frame isn't fixed; some learn earlier, and others later.

When Do Cockatiels Typically Start Whistling?
Most cockatiels begin whistling at around three months old, though the timing can vary. Each bird's natural talent and learning speed are different. If a cockatiel frequently hears other cockatiels whistling, it's more likely to start whistling earlier. Cockatiels are excellent mimics, so if they frequently hear their owner whistling, they can gradually learn to do the same.
Understanding the Motivation Behind Cockatiel Whistling
It's important to understand why cockatiels whistle to better teach them.
Communication with Other Cockatiels
The first motive is for communication with other cockatiels. This is the first step in their interactions. If you are at a distance or if the cockatiel cannot see you, try whistling simple tunes. As you whistle, walk towards the bird's direction. After a few tries, the cockatiel will understand that you're trying to communicate with it. It will then start responding to you, and it will begin to learn your vocalizations.
Expressing Affection and Emotion
The second reason is to express feelings. If you have an affectionate bird, it will be happy to share its emotions with you. When you approach it, it might get excited and want to interact. You can then whistle simple melodies to the bird. Cockatiels with a good ear will quickly learn the tunes. Whistling with them every day is more effective than playing recordings. It’s better to interact with your bird daily rather than relying on recordings for it to learn.