The original legendary Pokemon, Articuno, Moltres and Zapdos first appear in Generation I's "Pokemon Blue" and "Pokemon Red," though you can find the level 60 birds in games featuring the Kanto and Sinnoh regions. Capturing these legendary larks is an exercise in patience and restraint, as well as knowing which type of Pokemon and items to bring with you.
Gathering Preparation Items
If you're fighting legendaries, you don't want to overwhelm them. If you do, they'll faint and you can't catch them. This means you shouldn't bring any Pokemon that perform double damage to its type; for instance, don't bring a Water-type to fight Moltres. You also want to make it more difficult for the Pokemon to escape the ball, so use attacks like Hypnosis, Yawn and Stun Spore to stun your target or lull it to sleep; if it wakes up, be ready to put it back down. As an added bonus, bring a more powerful item to capture the Pokemon, such as a Great Ball or an Ultra Ball, which makes it more likely that you'll capture it the first time you throw the ball.
Defeating an Articuno
In Kanto, a single Articuno always waits deep in the caves of the Seafoam Islands, and "Pokemon X/Y" players can also find the bird roaming Kalos. You may also find one roaming randomly in Sinnoh once you've spoken to Professor Oak in "Pokemon Platinum." As an Ice- and Flying-type, Articuno will destroy Ice- Ground- and other Flying-types. Consider bringing a Bug-type like Weedle for its Stun Spores or a Poison-type to help knock down Articuno's health. Electric-types often come with great stun attacks, but their elemental attacks deliver double damage to a Flying-type, making them a last resort for any of the birds; however, Thunder Wave is an Electric-type move a Pokemon can use to stun without dealing damage.
Catching a Moltres
Like its brethren, Moltres has a healthy variety of attacks in its arsenal. Water-types do too much damage to this Fire-type, and Grass-, Ice-, Bug- and Steel-types will quickly fall in a match. When you find the fiery fowl on Victory Road or Mt. Silver in Kanto or roaming Kalos and Sinnoh, bring out your own Flying-type here; it will do normal elemental damage to Moltres, giving you the chance to whittle down its health and keep it stunned or asleep. When its health bar appears red and close to empty, throw a Poke Ball to attempt to catch it.
Capturing a Zapdos
Zapdos also roams Sinnoh and Kalos, but it primarily waits in the Kanto Power Plant and on Kanto's Route 10 when you've earned 16 badges in "HeartGold" or "SoulSilver." To combat its Electric-type attacks, keep the Water- and Flying-types at home. Ground-types also won't help you here; they deal too much damage while remaining susceptible to Flying attacks. Ghost-, Dragon- and Dark-types can all help here because none of the elements are weak to the other, giving you a fair fight.