Where do I find Chickens?

I wish to farm feathers (for arrows) but I cannot find any chickens. After searching I finally found 2 sheep but still no chickens, just hordes of cows and pigs.

Where are the chickens?

According to the Minecraft Wiki

Chickens naturally generate on grass blocks with 2 blocks of free space above it at light level of 9 or more.

which is more or less the same as what is listed for Pigs

Pigs spawn on grass blocks at a light level of 9 or more. Herds of pigs spawn upon world generation.

however the finer points on how animals spawn are located here

Approximately one in ten newly generated chunks will contain mobs, usually in packs of up to four of the same species. They will always spawn on the highest available block in a column, basically the one that can see the sky. For an animal to spawn on it, this block must be opaque and the two blocks above it must be transparent. The block does not need to be a grass block nor does it need to be illuminated as it does with mob spawning.

Animals do not spawn in desert or ocean biomes, with the exception of squid, and only mooshrooms will spawn in mushroom island biomes.

Randomness for animal spawning is derived from the world seed, which means that worlds with the same seed will generate chunks with the same animals in the same places.

the reason why your not finding any chickens could be your world seed has made the random chance of chickens spawning that bit harder over Cows and Pigs. the other reason could be that you yourself are just plain unlucky and the random selection of animal is just not giving you chickens.

Another Method to get arrows which doesn't require feathers is to kill Skeletons in which case you might want to do some research on Mob Grinders but remember they can also drop bones as well as arrows.

Also some Mods can allow you to have a source of certain items, Millenaire for instance if you find a village there is a chance they may have a chicken farm which will generate chickens for you to kill (if your quicker than the villager) or if you are in control of the village you can just loot it from the chicken farm's chest itself.