* Newspaper: Newspaper is a cheap and easy option for lining a cockatiel's cage. It is absorbent and can help to keep the cage clean. However, newspaper can be messy, and it can also be difficult to remove when it gets dirty.
* Sand: Sand is another popular choice for lining a cockatiel's cage. It is absorbent and can help to keep the cage clean. Sand is also relatively easy to remove when it gets dirty. However, sand can be dusty, and it can also be harmful if ingested by a cockatiel.
* Pine shavings: Pine shavings are a natural material that can be used to line a cockatiel's cage. Pine shavings are absorbent and can help to keep the cage clean. They are also relatively easy to remove when they get dirty. However, pine shavings can be dusty, and they can also be harmful if ingested by a cockatiel.
* Fleece: Fleece is a soft and comfortable material that can be used to line a cockatiel's cage. Fleece is absorbent and can help to keep the cage clean. It is also relatively easy to remove when it gets dirty. However, fleece can be expensive, and it can also be difficult to find.
Ultimately, the best choice of what to put on the bottom of a cockatiel's cage depends on your individual preferences and budget.