As long as they have grit available and plenty of actual food to eat this is not a problem.
I have only used pine shavings and so does everyone else i know.
But a hungry duckling with no food could eat enough to kill itself.
When ducklings are outside they pick up and eat alot of things.
I seen mine eat the shavings, but they never had a problem.
When they have grit it digests this kind of stuff no problem
