They are accompanied by their own music (composed by Nobuo Uematsu), which has remained relatively unchanged throughout the series; note that the music for chocobos is absent in final fantasy tactics.
Several different theories have been circulated about the origins of the species: some argue that the chocobos emerged with the monsters and black mages from the Mist in FF9, others argue it was years of evolution and adaption to the final fantasy worlds's varied climates.
There are different types of chocobos in different games: generally, a yellow chocobo is used for riding on the world map, and does not have any special abilities, besides preventing the rider from being drawn into a random battle. Also, on the world map, the chocobo moves faster than your character would normally walk. In final Fantasy 4 and 5, yellow chocobos can cross short streams.
In tactics, you may also be able to capture a wild chocobo and have it join your party: a yellow chocobo knows "choco cure" and "choco attack" and is controlled automatically; and cannot be equipped.
The following have special abilities in addition to being able to prevent the rider from encountering random battles and getting around on the map:
A black chocobo appears in Final Fantasy 4 and 5: they can fly short distances, and can only land in forests. In Final Fantasy 7, the Black Chocobo can climb mountans AND walk in rivers. It also appears in final fantasy tactics, and can fly 8 panels in any direction, and use "chocobo Ensuna" and/or "chocobo Ball"
A Light Blue chocobo: In final Fanyasy 9, it can cross rivers.
A Blue chocbo: In Final Fantasy 9, can cross dark water, and in Final fantasy 7, rivers.
A green chocobo: In final Fantasy 7, Can climb mountains.
a Red chocobo: Final fantasy 9, can climb mountains. In tactics, the red chocobo can use, in edition to chocobo ball, "chocobo meteor", which unleases a devistating attack on a single pannel. A hoarde of wild red and yellow chocobos can be devistating for even the strongest tactics party.
Gold Chocobo: Final Fantasy 7, can wade through oceans: is important in finding hidden materia, Knights of th Round.
There are also a variety of colored chocobos in Final Fantasy Unlimited, which don't have any apparant abilities other than the yellow one.
Ceil, the fated chocobo (FFU), can transform into a robotlike (?!) creature, and fly great distances and heights. (He can also be "summonned" in the series.)
Boco, who was bartz's chocobo/best friend in FF5, also appears in FF tactics, as a wild chocobo in a battle where ramza must decide whether to save him or not. saving him lets you enter him in your party. the newborn chocobo in FF9 is named BObby COrwen, as you can see "boco" in there.
In final fantasy 8, there are baby chocobos, also called "chicobos".
almot every final fantasy game after 6 has a "chocobo sidequest" of some sort: FF7 allows you to breed chocobos to get ones with different abilities, and to race them at the golden saucer. In FF8, you go through a whiole mess of explanation/instruction to ride a chocobo, but they have a minor sidequest for getting valuable items. In FF9, the "chocobo world" sidequest allows you to play a minigame where you dig for treasure, smiliar to the one in Link to the Past's Dark world treasure digging game. you can gain points, and "chocographs", which reveal hidden treasure throughout the world. In ff10, you must complete a series of trials such as dodging beach balls before you are able to obtain a chocobo. despite there being no world map in 10, the Calm Lands take forever to walk across without the help of a chocobo.
The chocobo feeds on Ghystahl Greens, Carrots, and is known to bite people's hair. It is also partial to the scent of the Dead pepper: however, when consumed, the chocobo goes temporarily beserk as the result of the spicy food.
occasionally, the chocobo communicates by emitting a "Wark" or "Kweeh" sound. Chocobos have shown remarkable intelligance, and are capable of understanding human language.
The "Fat Chocobo" (FF4) can speak human language, and although obese (as implied by his name), provides a very usefull service: he can store your excess items at no cost.
When barret got on the chocobo, it died because barret is fat.