Natural control of pests and disease

We get Thrushes in our garden they use an  old chimney pot to bash open snail shells there's usually a mound of shells inside.

I love to see that, but most birds (and squirrels) have the sense not to come down to ground level in our garden, as there are too many places where cats can hide in wait. The robins are braver, but they're bolshy little buggers