Answer: There are several possible causes, but usually birds would not be the culprit.
You might be seeing slug damage. Slugs are nocturnal and leave a silvery trail. They can be controlled using a bait containing iron phosphate. Read and follow the label directions.
You might be seeing flea beetle damage, if the holes are very tiny. These can sometimes be controlled by spraying with commercially formulated insecticidal soap, cultivating the soil around the plants, and by careful attention to garden clean up in the fall to limit their places for overwintering. Be sure to read and follow the label directions.
Or, you might be seeing damage by an animal such as a rabbit or woodchuck. These can sometimes be deterred by using a spray on repellent, these are sold at garden centers. Be sure to read and follow all label instructions for use.
You might also wish to consult with your local county extension for a more specific identification of the pest, and based on knowing that, recommendations for control.
Good luck with your garden this summer!
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