Once a year (ours always before it starts to get chilly) chickens molt. This is the process of losing feathers and regrowing new ones. During this period the chicken looks like its in severe distress. The very first time our hens went into a molt I panicked and thought they had some crazy disease, I spent hours googling chicken diseases to see what kind of crazy thing my flock could have come down with. It wasnt until I took a deep breathe and went back to my handy Stories guide to raising chickens book that i realized they were molting. Then I just had to laugh at them because they look so darn pathetic with clumps missing. I think they get self conscious because I see less of them during this period.
Some chickens will lose a large amount of feathers at once google chicken molting for some funny ones but mine always seem just to thin out in certain areas regrow and lose another feathers in another area. That drags the process on for a while, mine takes about 1-2 months for a complete molt. Sadly most if not all chickens will also stop laying eggs during this period so make sure you freeze eggs for this shortage. Most the time this molting process takes place in fall when due to decreasing natural light a chickens egg laying slows down naturally. My hens and many flocks will go into molt at the same time.
The good news:
Once she returns to laying you will see an increase in laying and better quality eggs as this break from laying gives her reproductive tract a chance to be rejuvenated.
Feather clipping comes yearly just after their molt finishes round here. Before anyone gets up in arms about this we do not harm our chickens, there is no blood or nerves in feathers, we do not pull them out or anything else like that. Now why we do clip the feathers is to stop chickens from flying the coop. There are feathers on the wings known as flight feathers after a molt and the chicken grows new flight feathers they must once again be trimmed.
I only trim one side of the bird which throws their balance off if they should try to fly. Most of my hens are GREAT and stay where they belong but the amerciuanas love to get over the fence and dig up my gardens and eat all my greens. So they are the FIRST to get a clipping after there molt!