On This Date in Missouri Senate History, the date was March 30, 1927, the day the Missouri General Assembly passed legislation designating the bluebird as the official state bird.
The eastern bluebird normally grows to between six and a half and seven inches in length.
Unfortunately, there’s no record of why the “native” bluebird — as it was called — was chosen, who decided on it, brought it to lawmakers’ attention, etc.
But — in any event — the “native,” or “Eastern” bluebird officially became Missouri’s state bird on March 30, 1927, on This Date in Missouri Senate History.
(Sources: Audubon Society, Missouri secretary of state, Missouri statutes and Missouri Senate Journal)