As part of its ongoing efforts to promote every single Pokémon out there, The Pokémon Company has shared special content dedicated to Articuno, Zapdos and Moltres:
Did you know?
Articuno: A legendary bird Pokémon. It freezes water that is contained in winter air and makes it snow.
Zapdos: This legendary bird Pokémon is said to appear when the sky turns dark and lightning showers down.
Moltres: A legendary bird Pokémon. As it flaps its flaming wings, even the night sky will turn red.
Source: The Pokémon Company