It can take ducklings 40+ hours to start zipping after the first pip. Many times they make multiple pips, near the first one, as they work their way into zipping position.
Pips can be hard to notice, shine your light across the eggs from all angles looking for bumps on the shell.
Here’s another pic of a zip. Once they start zipping, they shouldn’t stop more than a few minutes at a time. They hit the shell, rotate a little, then hit the shell again, right next to the last spot, which causes the end to break off, once they get all the way around. If they stop for more than 10-15 minutes at a time — once they fully start zipping — I break the cap off for them.
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