Here's a pretty good video by Tom Davis on O's hat history:
http://www.masnsports.com/ml/video.php?show_id=40418
It's pretty comprehensive, but I'm not sure this logo:

Was used from '76 on.

Going by my Topps Orioles book, I don't see that hat come up until the 1979('78 season)set, and it's only on two cards that I can tell. It's not until the 1980('79 season) set on, that you see every single player with that logo.

This one isn't even mentioned in the video, but in The Orioles Encyclopedia, there is one picture with this logo:

It's worn by Don Stanhouse, who was on the team '78-'79, and '82.

There are a few cards in the '79('78 season) Topps set, that look like they might have that logo, but it's hard to tell.

The logo that Tom says was used in '75 only, can be seen on caps through the '79('78 season) set.

There seems to be some possible overlap in the late '70's, which makes trying to figure this out a little confusing.

All this information leads me to believe that the following could possibly be the correct chronology for the the Orioles on-field Cartoon Bird logo:

L-R:
1. 1966-1974 - This is the only logo I've seen the players wear in pictures. Made by Wilson Sporting Goods.
2. 1975-1978 - Logo used on both white and orange panel('75-'76 only)alternate. Made by AJD.
3. 1975-1976 - Logo used on both white and orange panel alternate. Made by AJD.
4. 1978 - Made by Roman Pro.
5. 1979-1988 - Made by New Era(possibly Sports Specialties as well)

Well there it is, if anyone can add to this with player or team photos for more clarification, it would be great!