could be birds but horn worms will cut them like that. look for black droppings on the soil or mulch below the plant. if you see them, its horn worms. better look under the leaves too, they will strip a plant overnight.
they make some sprays and powders that only kill soft body insects made with DT earth. planting marigold flowers and basil in between the plants help a bunch too. marigolds scent confuses the moth when she tries to lay eggs. kind of like us putting on cover scent while deer hunting, lol. plus flowers in the garden help attract beneficial insects.