why do they peck a whole in their egg?

[Davaroo]

Unfortunately, egg pecking is likely to lead to egg eating in time. There is little grey area on this one.

As noted, egg picking mostly starts with a mechanical/accidental function: eggs cracked or broken for any number of reasons. Mislaying and stumble footing around in nest boxes are two common reasons for it. Nest crowding is another.

Also as noted, collecting eggs early and often is one way to mitigate it.

Lurid trickery, while appealing to the masses, is of little use. Fussing over blown eggs and filling them with noxious preparations has little effect, although WE love this sort of "country lore." But chickens dont have the same taste buds as we do, so things we find repelling don't phase them at all.
It mostly appears to "work," because we are by then alerted to the problem and so become more diligent about collecting

 

[Davaroo]

WildBurroShirts.com :

I also have some retarded (

really) EE's who pile up two and even three deep for some reason...so I think they kick the dang egg into the wooden side of the box when they do that.

Why do I think they're retarded? Because I have a 5 foot communal nest and a two foot 'private' nest: for 13 birds! With a six inch wide landing platform/front patio for them to walk back and forth on and choose their spot from.

There should be no sitting on each other's heads and shoulders with that much dang room!!!

This is also interesting. There seems to be no set mount of nest space that is universally satisfactory. Give them too much room, and they select one section or another and all crowd into it. Give them too little space, and they are forced to crowd, de facto.
Oh, I know what the recommendation is - 1 nest box for 4 birds. But this stems, in part, from the earlier efforts at intense floor rearing. It is more indutrial than pastoral. These are living things, after all, and they dont aways follow our "rules."
I was never so amused as the time I found 4 chickens all crammed into one nest box! They did this day after day. While they were also laying in other nest boxes, that one seemed to hold some special fascination. They seemed as happy as could be... I was concerned that any eggs in that box would be trampled.​