The most common and most likely answer to this crossword clue is the 12 letter word YELLOWHAMMER
I've seen this crossword clue in Financial Times
Y
E
L
L
O
W
H
A
M
M
E
R
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 = yellowhammer.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 YELLOWHAMMER mean?
YELLOWHAMMER noun- A passerine bird, Emberiza citrinella, of western Eurasia, which is mainly yellow in colour.
- The northern flicker, Colaptes auratus.
- A native or resident of the American state of Alabama.