I have a bird. This is my bird.

我养了一只鸟，这是我的鸟。

We have a bird, a dog and a cat.

我们家里有一只鸟，一条狗和一只猫。

I have a bird. The bird is white.

我有一只鸟。它(这只鸟)是白色的。

I have a bird. Its name is Polly.

我有一只鸟，它叫波利。

I have a bird. It's small.

我有一只鸟，它是小的。