yardbird

noun Slang.

1. a convict or prisoner.
2. an army recruit.
3. a soldier confined to camp and assigned to cleaning the grounds or other menial tasks as punishment for violation of the rules.

noun

1. US military an inexperienced, untrained, or clumsy soldier, esp one employed on menial duties

n.“convict,” 1956, from yard (n.1) + bird (n.1), from the notion of prison yards; earlier it meant “basic trainee” (World War II armed forces slang).