The most common and most likely answer to this crossword clue is the 8 letter word SWIFTLET
I've seen this crossword clue in The Times
S
W
I
F
T
L
E
T
Buddy explains!
The straight part
We know that "Bird" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bird = swiftlet.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SWIFTLET mean?
SWIFTLET noun- Any of the various tropical and subtropical birds of the four genera Aerodramus, Hydrochous, Schoutedenapus, and Collocalia in the swift family, many of which can navigate in darkness using echolocation.