The most common and most likely answer to this crossword clue is the 6 letter word FALCON
I've seen this crossword clue in Independent
F
A
L
C
O
N
More clues leading to the result FALCON
- Bird caught on Cornish river to the west
- Rook by Cornish river is a high-flyer
- Calf moving about on bird of prey
- Bird, loud, a large rook
- Criminal chasing fellow gangster gets bird
- Short trip to study bird
- Bird flu affects little children, only not at first
- Bird in brief dive, gull
- Bird entrails, but not of rook
- Cannon left loaded, the French way
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 = falcon.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 FALCON mean?
FALCON noun- Any bird of the genus Falco, all of which are birds of prey.
- A female such bird, a male being a tiercel.
- A light cannon used from the 15th to the 17th century; a falconet.
- To hunt with a falcon or falcons.