The most common and most likely answer to this crossword clue is the 5 letter word CRAKE
I've seen this crossword clue in The Daily Telegraph
C
R
A
K
E
More clues leading to the result CRAKE
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 = crake.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 CRAKE mean?
CRAKE noun- Any of several birds of the family Rallidae that have short bills.
- To cry out harshly and loudly, like a crake.
- A crack; a boast.
- To boast; to speak loudly and boastfully.