Strawberry Problem

[megfitz]

Several plants(Everbearing) grown through black plastic have leaves that have big holes munched in them and some flower stems are brown and dead.
I have checked the plants and the soil under the plastic...no sign of any nasties e.g. weevils or aphids ,could this be birds/ snails?? There is a seep hose spread through the Veg patch so they are watered adequately. I garden organically so no chemicals but any advice on diagnosis or treatment appreciated.