What to do with cabbage white caterpillars?...

Hello all,
I've noticed that there are a lot of cabbage white caterpillars on my nasturtiums this year. I'm not too bothered about the nasturtiums being eaten but I know the cabbage white is considered a bit of a pest and i'm not sure what to do about them. I am trying to garden organically and for wildlife. Once they have munched the nasturtiums will they move on to other things in the garden? If I just leave them where they are will the birds eat them?
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It does make you realise why the farmers have to spray their crops, when you see the amount of caterpillars we get in our little garden, if it was a cabbage crop it would have been decimated !!!