Let us examine all of the evidence. Birdo, Boy or Girl?

[elgefe02]

Sex and Gender

According to the North American instruction manual of Super Mario Bros. 2:

"Birdo thinks he is a girl and likes to be called Birdetta. He likes to wear a bow on his head and shoot eggs from his mouth."

This statement applies to all translations of the title, including the Japanese version. In Japan, Catherine is male as well, and likes to believe that he is female. Like Birdo, he likes to be called Cathy as opposed to his real name, Catherine. In Super Smash Bros. Brawl, Birdo's trophy description describes the character as "gender indeterminate," and uses the pronoun "it" rather than gender-specific pronouns such as "he" or "she".

The confusion surrounding Birdo's gender has also been addressed in a light-hearted matter, such as when Popple pauses before settling on calling Birdo a "dame" in Mario & Luigi: Superstar Saga. More recently, in the game Captain Rainbow, Birdo is heard with a deep, male voice which gets high-pitched when she gets angry or excited. Additionally, in the game's second trailer, Little Mac from Mike Tyson's Punch-Out!! speaks about Birdo, calling her a "young lady," only to take a short break and ponder. His final verdict is "Depending on one's view point, she is a young lady." This ultimately means some or all of these Birdo characters identify with the female gender.

Powers and Abilities

In addition to eggs, Birdo can shoot fireballs from her snout, though this ability is only displayed in Super Mario Bros. 2 and its subsequent remakes. Birdo has also shown the ability to utilize her snout in a manner similar to a vacuum, using her to suck things closer to herself or even swallow them; Birdo displays this ability in both Mario & Luigi: Superstar Saga, which notably has her leeching away the health of those she sucks up, and Mario Superstar Baseball. Birdo has also shown, on occasion, to envelop people, including herself, in large eggs, in order to increase defense. She is usually classified as all-around in sports games, where she has a great deal of strength.

In Mario Golf: Toadstool Tour hitting a nice shot while playing as she will cause a rainbow to form similar to Yoshi, but rainbow abilities have since then not been seen. Birdo also has some hints of heart based power similar to Princess Peach as shown in Mario Golf: Toadstool Tour in her victory cut-scene and Mario Hoops 3-on-3 in her special shot. However, they are not as strong or as useful as Peach's hearts; which often results in comedic instances, such as when they only succeeding in charming Birdo's Golf trophy into the air for a short time until it fell down again, to her owner's great surprise.

Relationship with Yoshi

Yoshi and Birdo are often partners in sports and party games.In Mario Kart: Double Dash!!, Mario Tennis, Mario Party 7, and Mario Party 8 they are defult partners. They were seen nuzzling each other on the title screen of Mario Tennis,in wich they also share a Tennis Court. The ring Birdo wears is suggestive, but likely unconnected. On the official site for Mario Kart: Double Dash!! the description for Catherine states "Catherine appears to be Yoshi's girlfriend... or does that mean boyfriend?!". Also in Mario Hoops 3 on 3 they appear at Mario Stadium. In Mario Superstar Baseball and Mario Super Sluggers Birdo is Yoshi's Sub-captain, also they share good Chemistry.

Physical Description

Birdo's appearance

Birdo is a pink dinosaur; however, she is not the same species as Yoshi. Her head is shaped similarly to that of Yoshi's, but her mouth is quite different, as it is shaped somewhat like a funnel. Birdo's belly is white amd fairly rounded. Her body is shaped nearly identically to Yoshi's and they are approximtely the same height.

Birdo commonly wears purple eye makeup. In her team name, "Birdo Bows", from Mario Super Sluggers, she wears lipstick, which is odd because she doesn't use lipstick during the game, nor in most of her other appearances. She hasn't hair and atop her head is a massive red bow, and on her left hand is a large diamond ring, the origins of which are unknown. In the Mario Football series, Birdo wears a two-piece soccer outfit composed of a jersey and shorts. In the Japanese commercial for Super Mario All-Stars, she wears a very expensive black dress, adorned with a black necklace with many pearls, also she wears a white stole, and a very elegant fan.

 

Source: http://www.mariowiki.com/Birdo#Sex_and_Gender