I don't assume the birds came from the island(and why? you may ask? They didn't have a Dharma logo ).... bird migrate at great distances. They are the wild card in the control issue, especially if the purple sky thing shut down the whatever so that now the island is not shielded.

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`Dear, dear! How queer everything is to-day! And yesterday things went on just as usual. I wonder if I've been changed in the night? Let me think: was I the same when I got up this morning? I almost think I can remember feeling a little different. But if I'm not the same, the next question is, Who in the world am I? Ah, that's the great puzzle!'

-- Alice, from “Alice’s Adventure’s in Wonderland”