why are most bird pokemon dual type?

Question

Ive never known a pure flying type or maybe theres only one I heard but why are they all dual typed

Answer 1

Legendary pokemon Tornadus from Black/White is the first and only pure Flying type.

All other Flying types have Flying as the secondary type, most commonly with Normal. The exact reason it was like that is unknown. In most games, the first routes are nearly all Normal type, so this is probably why pokemon like Pidgey have the Normal type.

Then they just carried on that trend with Spearow, Starly and so on. So any pokemon based on birds are Normal/Flying unless there is a call for a different type like Water/Flying. Tornadus is based on a tornado, not a bird, so is pure Flying.

Comments

Don't forget the Roost situation Pokemaster, they lose their flying half on the turn they roost

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Which explains why they would continue to do so from Gen IV and up, but not why before then J98.

Answer 2

I heard somewhere that if a pokémon uses Roost, they lose their Flying type or something. If so, it would give them a type to have after using Roost.

Comments

"I heard somewhere". Was it perhaps the comment above this answer?

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Hmmm... Interesting...