"bird," 1531, grows (pl., used collectively), of unknown origin, possibly from Latin or Welsh.
"complain," 1887, British Army slang (first recorded by Kipling), of uncertain origin but perhaps from Norman Fr. dial. groucer, from O.Fr. groucier "to murmur, grumble," of imitative origin (cf. Gk. gru "a grunt," gruzein "to grumble").