Transparent Egg - What caused it?

[aart]

There is usually only one egg in the nest box & today there was this and one whole egg.

That can happen, second egg did not get shelled.

 

[007Sean]

They can't 'produce' more than one egg a day but they can 'lay' more than one a day. At the time of the first egg is layed, 30 minutes later a new ova will be released.
Another 30 minutes and the yolk will enter the reproductive tract where it gets incased in a thin membrane. Then for about 3 hours the albumen starts forming around the membraned yolk.
The encased yolk continues to travel and begins to take on the oval egg-shape, then another double membrane is formed around the whole thing, this takes about an hour.
Then the membraned yolk will enter the uterus where the shell is created, taking about 20 hours
Brown pigment is applied to the eggshell in those birds that lay brown eggs, blue pigment is applied earlier in the process in those birds that lay blue eggs and brown is applied over the blue in the green egg laying breeds, this happens in the last 5 hours of the shell being laid down. This occurs in the egg shell pouch.
The final coat is a clear coating called the "bloom" or "cuticle" it's applied to the surface of the shell. This coating helps to keep air and bacteria out of the egg. This takes about another hour.
Another 30 minutes or so will pass and the egg is ready to be laid.

It's at this point the hen can 'delay' laying the egg, due to stress, or other environmental irregularities.
If this delay occurs after dark it won't be until early morning before the egg is laid. At this time another ova has already been released and is traveling down the reproductive tract and by the late afternoon the hen could lay another egg....appearing to have layed 2 eggs in one 24 hour period.
But only 1 ova can be produced or released in the 24 to 26 hour period.
Sometimes 2 ova get released at the same time, this can result in the same appearance of two eggs in one day or can result in a 'double yolked' egg.

 

[chkva]

Layer feed and oyster shells or eggshells would help a lot with these types of eggs. New layers and hens need calcium to form hard shells.

I only give scraps at night around 6 p.m. after my hens have been eating their layer feed all day and free ranging. Feeding them scraps at night ensures that they've had enough layer feed and protein for the day.