What causes ducks to eat feathers?

Why do ducks eat feathers? A duck eating feathers is not a disease, but eating the feathers off other ducks is a sign of disease.

If you observe carefully, you will find that when a duck “eats feathers,” it first pecks at the tail, then moves over the whole body.

Scientists have found through dissection that at the tail of a duck there is a sebaceous gland that secretes oil; the duck dips its hard bill into this oil and spreads it over its whole body, which gives it a waterproofing effect.

When a new duck starts eating the feathers off other ducks, first, this duck is in a diseased state; it lacks calcium in its body, and calcium can be supplemented by feeding it fish bone meal or shellfish shells.