Green’s Dictionary of Slang

bird n.4

[rhy. sl. birdlime n.2 (2) = time n. (1)]

1. [1920s+] a prison sentence; do bird, serve a sentence.

2. [1930s–40s] previous convictions.

3. [1950s–60s] in fig. use, any form of constraint, responsibility.

In compounds

bird-happy (adj.) [ -happy sfx]

[1970s] (UK prison) emotionally affected by a (long) prison sentence.

birdhouse (n.)

1. [1940s] (US) a prison.

2. [1950s] (US drugs) a place where one can purchase narcotics [puns on birdseye n. (3) + SE house].

3. [1950s] a psychiatric institution.

In phrases

first bird (n.)

[1920s+] (UK prison) one’s first experience of a prison sentence.