We currently have the general avian, which for a long time has been described (in terms of the tag wiki excerpt) as
For questions about birds and birdlike creatures.
After a recent edit by yours truly, it is now described as
For questions about birds and birdlike creatures. Does not include machines designed for flying (consider [airships], [aircraft], [spaceships]). Consider also [flight].
However, there is currently no tag birds
I propose that birds
is established as a tag synonym, with the canonical tag being avian
as birds
is more discoverable, but avian
is more generic.
See also discussion on the factory floor, beginning here (link to the chat transcript).