Birdo, known in Japan as Catherine (キャサリン Kyasarin ), is a fictional, anthropomorphic dinosaur-like creature featured in Nintendo's Mario series of video games. Nintendo has never made the exact nature of Birdo clear, appearing as both a particular character and a species of character, just as Yoshi from Super Mario World can refer either to a class of video game dinosaurs or a particular one. Birdo first appeared in the Japanese game Yume Kōjō: Doki Doki Panic as a minor boss appearing at the end of many of the levels. Yume Kōjō: Doki Doki Panic was later remade into Super Mario Bros. 2 for worldwide release, later known as Super Mario USA in Japan.
Birdo is most frequently depicted as pink, although red, green, blue, yellow, orange, and gray Birdos are also seen in Super Mario Bros. 2 and other games; gray Birdos were changed to green in the remakes due to their attack patterns matching. In Super Mario Bros. 2, Birdo would spit out eggs and/or fireballs from her tubular snout.
After defeating Birdo by grabbing her eggs while riding them and throwing them at her three times, Birdo would drop a crystal ball that would allow the player to open up a gate called "Hawkmouth", which led to the next level. Although it would appear that the crystal ball drops out of Birdo's stomach, promotional art for Super Mario Bros 2 and Yume Kōjō: Doki Doki Panic show that Birdo is actually holding the object in his hands. This would later change in the Super Mario Bros. 2 remakes in Super Mario All-Stars and Super Mario Advance, in which Birdo spits the crystal out of his mouth after being defeated. In the final level of Super Mario Bros. 2, World 7-2, Birdo actually drops a key, which the player must use to open a locked door and finish the level.
Birdo can also be helpful, such as in World 4-3 of Super Mario Bros. 2, where the characters can jump onto an egg and ride it over an extra-wide chasm, much as they can ride on an Albatoss in other levels. Birdo is not carrying anything in this level.
In later games such as Mario Tennis, Birdo's personal icon is her bow ribbon, much as Mario's is the red "M" logo from his hat. Though Nintendo's official drawings of Birdo have always depicted her as wearing a bow, it did not actually appear on her head in games until the Super Mario All-Stars revision. In Super Mario Advance, Birdo's bow can actually be taken off her head and thrown away; if it hits Birdo, it will simply reappear on her head. Super Mario Advance also features a new boss character in the form of Robirdo, a giant, robotic Birdo.
As of Mario Golf: Toadstool Tour, the individual Birdo character now wears a diamond ring. However, in Mario Strikers Charged, it seems all Birdos now wear diamond rings. 
In the The Super Mario Bros. Super Show!, Birdo could fly and had a nest set atop a high peak. However, Birdo has later been confirmed unable to fly in the game continuity.
Gender and species
Although Nintendo of America classifies Birdo as female and some classify it as transgendered, the first edition game manual for Super Mario Bros. 2 describes Birdo as follows: "He thinks he is a girl and he spits eggs from his mouth. He'd rather be called 'Birdetta.'" Based on this description, it is arguable that Birdo is the first transgendered video game character. Subsequent printings of the game manual delete the Birdetta sentence but retains the first description.
In Japan, Birdo is known as "Catherine" and purportedly enjoys being called "Cathy". However, the Birdo character has always been male in the original Japanese versions. Presumably to avoid controversy, Nintendo of America has localized Birdo as female in future appearances of the character. It was speculated that Birdo was possibly transgendered, and Nintendo of America would eventually retcon this tidbit to avoid raising any concerns about the character's transsexuality. Confusion has also arisen over Birdo because the names for Birdo and Ostro, an ostrich that playable characters can ride, were erroneously switched in the Super Mario Bros. 2 end credits  as well as in the game manual. Since then, many have confused the two to the point of calling the actual species "Ostro," and believing that the 'main pink one' was individually named "Birdo." Super Mario Advance, a game which contains a remake of Super Mario Bros. 2, does not repeat this mistake.
Recently, Birdo has been noted as a male on the official European Mario Strikers Charged Football website and in the game manual.
Robirdo is a boss in Super Mario Advance. It is a giant, robotic version of Birdo. The fight against Robirdo replaced a Mouser battle that was in Super Mario Bros. 2.
Robirdo jumps, shaking the ground and stunning Mario, Luigi, Princess Peach, or Toad if they are on the ground. Then, it runs forward. Another attack is spitting two giant eggs. All three of these attacks can be evaded by climbing the chains that hang down in the room. Like the regular Birdo, Robirdo can be defeated by throwing eggs back at it.
Super Mario Bros. 2 and the various remakes of that game are the only Mario platformers where Birdo has appeared.
Although never appearing in any of the 3 Paper Mario games, Birdo has appeared in Super Mario RPG: Legend of the Seven Stars and Mario & Luigi: Superstar Saga. In the former game, Birdo was a minor boss character that appeared in the castle of Nimbus Land; Birdo's egg must be cracked and broken before Birdo actually appears. In the latter game, it is revealed that she was magically disguised as Princess Peach when the Mushroom Kingdom got word that there was going to be another kidnapping attempt on her; when Cackletta and Fawful steal Peach's voice, they really steal Birdo's. She appears when the deception is revealed, and later becomes enamored with Popple the thief (or she could be teasing him), joining him for his second last battle against Mario and Luigi; but leaves him after they are defeated. Birdo is referenced in Super Paper Mario. In the Sammer Kingdom, there is a Sammer Guy who named himself Squatting Birdo.
Mario Kart and sports
Birdo, as the character, has appeared in several Mario sports titles.
Nintendo had left Birdo out of most Mario titles before the Nintendo 64 installment of Mario Tennis, where she made her first-ever appearance as a controllable character, and was Yoshi's default tennis partner for doubles matches. Since then, Birdo appeared as a playable character in several Mario sports titles: Mario Golf: Toadstool Tour, Mario Kart: Double Dash!!, Mario Superstar Baseball, Mario Hoops 3-on-3 and Mario strikers charged.
As a race, Birdos appeared in the stands of Mario Power Tennis, as opposed to a playable character like its predecessor. In Super Mario Strikers and Mario Strikers Charged, the Birdos are both a generic color-swap character that the player can use and spectators of the games.
Mario Party 7 is Birdo's first appearance as a playable character in the Mario Party series. To unlock Birdo, get 1,000 mileage points, then buy her at the Duty-Free Shop. Note that her ring in Mario Party 7 is used to classify her from other Birdo. Birdo is also now playable in the Wii game Mario Party 8.
In Wario's Woods for the NES and SNES, Birdo appears in the tutorial. Birdo also makes an appearance in Super Smash Bros. Melee as part of the Mushroom Kingdom 2 stage, but is not a playable character. Instead, she appears from either side of the screen and shoots eggs at combatants and can be attacked and defeated by players. She also appears as a collectible trophy in that game; when this trophy is obtained, it unlocks Mushroom Kingdom 2. Birdo also makes a cameo in one of the backgrounds of the Super NES title Kirby Super Star, alongside Mario, Luigi, and Toad. This is unusual in that Birdo had not joined the ranks of Mario regulars at this point.
Birdo was never a prevalent character, so appearances outside of the games are minor. Birdos appeared in The Super Mario Bros. Super Show, but two episode had Birdos mistaken with wings: a mother and child in the episode "The Bird! The Bird!".  and "On Her Majesty's Sewer Service". Birdos have also appeared in the episodes "Butch Mario & the Luigi Kid", "Toad Warriors", "Jungle Fever" and in "Escape from Koopatraz" as part of the jury, but did not appear in any of the later Mario cartoons.
In the comic books, Birdo makes only a few appearances; in the story "The Adventures of Dirk Drain-Head", Birdo appears to attack Mario and Luigi, and it is later revealed that Bowser buys "Baroness Blue Blood" comic books for the purpose of "lining his birdo cages". 
A song written about Birdo, 'Birdo', is featured on HORSE the band's album, The Mechanical Hand.
The Birdos from the Super Mario Brothers Super Show clearly spoke English. In Mario Tennis for the N64, Birdo spoke English, and had a very high-pitched voice. She said things like "Okay" and "Alright". Birdo also speaks clear English in Super Mario Advance, a remake of Super Mario Bros. 2, threatening the player by saying "this is as far as you go!" She speaks fluent English (in text form) in Mario & Luigi: Superstar Saga and Super Mario RPG: Legend of the Seven Stars.
In Mario Golf: Toadstool Tour and all later games, she only says "Birdo", in a way similar to how Yoshi only says "Yoshi", and also makes a series of quacks and honks. Birdo's language is extremely vague, and very little is known about it. Subtitles in Mario Golf: Toadstool Tour seem to hint that the more low-pitched the sound, the happier it is (compliments are all low-pitched and taunts are all high-pitched); however, in Mario Kart: Double Dash!!, her honks are all low pitched with the exception of her winning phrases. In Super Mario Strikers, all of her honks are high pitched. Typically, the only understandable word that Birdo will utter is her own name, akin to Yoshi.
In The Super Mario Bros. Super Show!, she was voiced by Jeannie Elias who also voiced Princess Toadstool.  In Mario Tennis, she was voiced by Jessica Chisum. In Mario Golf: Toadstool Tour, she was voiced by Isaac Marshall.
The various games which have featured Birdo, and their instruction manuals.
- "Ending for Super Mario Bros. 2". http://www.vgmuseum.com/end/nes/a/mario2.htm. Retrieved 2005-12-18.
- "The Bird! The Bird! / Neatness Counts". TV.com. http://www.tv.com/the-super-mario-bros.-super-show!/the-bird!-the-bird!---neatness-counts/episode/123352/summary.html?tag=ep_list;title;0. Retrieved July 30 2006.
- "The Adventures of Dirk Drain-Head" Adventures of the Super Mario Bros. 3: 10/bottom (April 1991), Valiant