Birdo is one of
Nintendo's most confusing characters. The instruction manual for
Super Mario Brothers 2 claims that he "wants to be a girl" and "would rather be called 'Birdetta". He's a pink, standing-upright dinosaur with a cannon-like snout that fires eggs at
Mario and friends. He even wears a frilly bow upon his head. As the character began to appear in subsequent games
Nintendo, obviously concerned about controversy, began to refer to Birdo as a she, and the matter of Birdo's
sexuality was never raised again. Perhaps Birdo had some major surgery during her downtime between 1988's
SMB2 and 1993's
Super Mario All-Stars.
In all of the different variations of Super Mario Brothers 2 (such as Super Mario All-Stars, Super Mario USA, BS Super Mario USA, Super Mario Advance, and the original game that spawned them all, Doki Doki Panic) Birdo's primary function is to guard the eagle's head gate. She does this by spewing eggs from her snout which Mario and friends can grab and toss back. Three hits defeats her, and she'll give up the crystal ball when she goes down. Picking up that item opens the gate. As the game progresses the pink Birdos give way to red ones that spew both eggs and deadly fireballs. Even later in the game comes the green Birdo that spews only fireballs. It's up to Mario to use items in the room to score damage, such as mushroom blocks. In Super Mario Advance Mario can even jump on her head and pull off her bow just for fun. Throwing her own bow back at her only causes it to appear back on her head. Occassionally Birdo appears in other places in levels which is a sign that her eggs are needed as a source of transportation and not as a weapon. Furthermore, the end of World 3 in Super Mario Advance features a giant robotic Birdo boss.
Birdo didn't appear again until Super Mario RPG where she was a major boss in the cloud castle. After Mario and his friends cracked open her egg, she appeared and fired eggs to dish out lots of damage. Mario and friends could defend, however, to make the eggs bounce back harmlessly. In fact, this was the key to surviving the onslaught and defeating her nearly effortlessly. Birdo has 777 HP in this encounter. Birdo's next RPG appearance wouldn't occur until 2003's Mario and Luigi: Superstar Saga where she falls in love with one of the land's many thieves.
Wario's Woods sees Birdo watching the action from above the playfield until Wario appears. Speaking of playfields, sports appears to be one of Birdo's hobbies. She has a cameo in Super Smash Bros. Melee in the Mushroom Kingdom II level where she fires eggs into the arena. She's appeared in both Mario Tennis, Mario Golf, Mario Golf: Toadstool Tour, and Mario Kart: Double Dash!! in recent years as well. She typically teams up with Yoshi, which has led some to speculate that there may be some romance between the two dinosaurs. I wonder if Yoshi knows she was once a male? Either way, Birdo's come a long way from the crossdressing gate guardian she debuted as in 1988.
References:
SMB2 instruction manual
http://www.classicgaming.com/tmk/
http://transsexual.org/birdo.html