The most common and most likely answer to this crossword clue is the 4 letter word GAOL
G
A
O
L
More clues leading to the result GAOL
- Convict upset about old place of confinement
- Good internet service provider creating stir
- Bird starts to glide away on landing
- Nick‘s girl taking over
- Criminal upset getting old inside prison
- Person with convictions upset about old prison
- Prison inmate’s over getting old inside
- Miss hugging Old Nick
- Prison record from the East covering start of action
- Girl's love is in jail
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 = gaol.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 GAOL mean?
GAOL noun- A place or institution for the confinement of persons held in lawful custody or detention, especially for minor offenses or with reference to some future judicial proceeding.
- Confinement in a jail.
- The condition created by the requirement that a horse claimed in a claiming race not be run at another track for some period of time (usually 30 days).
- In dodgeball and related games, the area where players who have been struck by the ball are confined.
- (FreeBSD) A kind of sandbox for running a guest operating system instance.
- To imprison.