There is no such thing. Birds and mammals are distinct from one another.
There isn't a mammal-bird.
No. Whether it is tropical or not, no bird is a mammal.
There is no such thing. No bird is or ever was a mammal.
No. A budgerigar (budgie) or parakeet is a bird, not a mammal.
mammal
A mammal.
The only thing I can imagine you are asking about is a Bottlenose dolphin, and it is a mammal.
If a bird were to give birth, it would not be considered a bird, but a flying mammal with feathers.
Bird
A penguin is a bird or a vertibrate animal. Mammals are animals which only give birth to live young (with the sole exception of the platypus, which lays eggs).
A chickadee is not a mammal. It is a bird.
A stork is not a mammal. It is a bird.