"P" just asked me why her chickens aren't laying eggs. This is the time of year that they should be producing lots of eggs, here in Hawaii. Without looking at her flock, I gave her a list of possible causes. Here's what we discussed (based upon my own observations).....
...too young. This turned out to be "P's" problem. Her hens might look big and ready, but they are only five months old. Most of her hens are breeds that don't lay until 6-9 months old.
..too old. Hens slow down after 2 years of age. I have some 8 year olds that are still laying, but it's only a few per week and they stop early in the laying season. If they lay for 2-3 months, that's pretty good for their age. I also have two banties that are most likely 10 to 12 years old and still laying a few eggs. Amazing little birds.
...broody. When a hen gets broody and sits on eggs, she stops laying more eggs.
...not enough food. Letting the hens run out of food can lead to less eggs. If they are out of food for a couple days, they usually quit laying altogether for the season. Less food = less eggs.
...inadequate diet. What they are being fed is important. If they are penned and fed a diet lacking in nutrients, their egg laying will be severely affected. Poor diets often means no eggs.
...significant change in diet. A seen change room commercial pellets to all pasture, or changing from crumbles to seed based can significantly change egg laying habits.
...no enough water. Egg laying takes water. When hens run out of water or don't get enough each day, egg production decreases or ceases.
...adverse weather. Too hot or too cold. No rain protection in areas of high rainfall.
...lack of available nest space. Most hens will keep laying eggs even if no nest boxes are provided. But some will shutdown if they can't have a private spot for egg laying. It depends upon the individual hen.
...molting. Hens stop laying eggs from when they get ready to molt up to the time that they've grown fresh feathers.
...illness. Sick hens stop laying.
...parasites. Both internal and external parasites can affect egg laying.
...physical injury. It's not uncommon for an injured bird to stop laying.
...emotional stress. Drama in the flock (new birds), fighting, commotion outside the pen (construction, dogs, helicopters overhead, etc)
...being the low man in a crowded pen without hiding places. The low status bird may not lay.
...wintertime. Daily light is shorter during the winter. Egg laying is tied to the length of day. If lights are provided during short days, hens will continue to lay. But if no additional light is provided, hens will follow Mother Nature's guidelines and stop laying.
I haven't made all these "mistakes", but admit I've done a few while I was learning about chickens and egg production.