From the late-60's to the comic's demise in 1984, potentially thousands of young British readers were led to believe that Tweety was a girl (this was in the days before Warner Brothers started to market Tweety merchandise to girls, hence the current confusion), while children on the other side of the pond were reading the Dell Comics versions where the canary is clearly referenced as male.
Hard to believe, ain't it? But alas, I provide the proof.
Below are five examples of where Tweety is often referred to as a she. Enjoy or weep, it's up to you.