Noticed three of the copyright tags at post #273106 (an absolutely_everyone convention image) are
birdman, harvey_birdman and harvey_birdman_attorney_at_law.

3 posts tagged with birdman:
1) post #2019266 (FA version says "Horus")
2) post #372804 (deleted at FA; referred to as "that bird thing" at artist's pixiv so probably unnamed)
3) with post #273106 the "birdman" is Harvey_Birdman (near bottom-left in the Maid Cafe).

-> birdman_(disambiguation) ??
(Some other bird*man* :
bird-man_of_aberdeen character tag
https://creepypasta.fandom.com/wiki/The_Bird-Man )

RE: Harvey_Birdman* tags:

Harvey Birdman is the character
https://en.wikipedia.org/wiki/Harvey_Birdman
How about harvey_birdman tag be changed from type copyright TO type character??

Cartoon series named "Harvey Birdman, Attorney at Law"
https://en.wikipedia.org/wiki/Harvey_Birdman,_Attorney_at_Law
so harvey_birdman_attorney_at_law copyright tag should be fine (since i don't see any e621 tags with a comma)

4 posts tagged with harvey_birdman:
1&2) post #1680323 and post #273106 (which do include Harvey)
3) post #191980 : which doesn't include Harvey, but does include Avenger (another character from the cartoon series). https://harveybirdman.fandom.com/wiki/Avenger
4) post #40761 : only character depicted is Bear, another character from the cartoon series ( https://harveybirdman.fandom.com/wiki/Bear )

Only one upload tagged with harvey_birdman_attorney_at_law,
the absolutely_everyone convention image.