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http://pixelmonmod.com/wiki/index.php?title=Legendary
If you click this link. You'll see every game currently in the mod. Click the name (not the image) of the bird you wish to look up.
You'll find a square on the right side with a box for "Biomes", and a box for "Spawn Time". This gives you some information on where to search for the birds.
Good luck.
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