1. The bird flies in the sky.
2. Any bird flies in the sky.
3. The specific bird flies in the sky.
[Does #1 mean #2 or #3?]
4. The bird is flying in the sky.
5. Any bird is flying in the sky.
6. The specific bird is flying in the sky.
[Does #4 mean #5 or #6?]
The bird flies in the sky. OR The bird is flying in the sky.
The eagle flies in the sky. OR The seagull is flying in the sky.
#1 and #4 will have similar meanings if you include a specific type of bird in #3 and #6.
(I would not use #2 or #5.)