The origin of the song, according to songwriter David LaFlamme, who co-wrote this 1969 classic with then-wife Linda LaFlamme:
Where the ‘white bird’ thing came from … We were like caged birds in that attic. We had no money, no transportation, the weather was miserable (in Seattle). We were just barely getting by on a very small food allowance provided to us. It was quite an experience, but it was very creative in a way.
https://www.youtube.com/watch?v=XUNgQ03D2qA